fix(types): refine alias skipping logic in type comparison functions

fixes #25800
closes https://github.com/nim-lang/Nim/pull/25807
ref https://github.com/nim-lang/Nim/issues/25800

This pull request improves the handling of move semantics and the
`=wasMoved` hook in the Nim compiler, especially for C++ code generation
and user-defined types. It refactors the move operation logic to better
support custom hooks, adds new tests for edge cases, and ensures that
the `move` operation is safer and more predictable.

**Move semantics and `=wasMoved` handling:**

* Refactored the move operation in `compiler/ccgexprs.nim` by
introducing helper procs (`canGenMoveCall`, `genMoveCall`,
`genWasMovedCall`, `genMoveWithWasMoved`) to better handle cases with
user-defined `=wasMoved` hooks, especially for generics and C++ interop.
The logic now distinguishes between simple assignments and when to call
custom hooks, improving correctness and maintainability.
[[1]](diffhunk://#diff-4509107d295d7d32b1887c8993cd0f56113ae60f36113e7d8778646dabd92ebcL2818-R2851)
[[2]](diffhunk://#diff-4509107d295d7d32b1887c8993cd0f56113ae60f36113e7d8778646dabd92ebcL2841-R2882)
* Updated the `move` proc in `lib/system.nim` to include the `nodestroy`
pragma, preventing double destruction and making move semantics safer.

**Testing and validation:**

* Added a new test (`tests/ccgbugs2/t25800.nim`) to ensure that
user-defined `=wasMoved` hooks with `{.importcpp.}` are correctly
generated and invoked in C++ code, addressing a specific bug with
invalid preprocessor directives.
* Expanded `tests/destructor/twasmoved.nim` with additional test cases
for objects with and without custom `=wasMoved` hooks, including
multithreaded scenarios using `threadpool`, to verify correct behavior
in a variety of contexts.

**Minor cleanup:**

* Added a blank line for code style consistency in
`compiler/semmagic.nim`.

changelog.md

@@ -35,6 +35,10 @@ errors.
 
 - Adds a new warning `--warning:ImplicitRangeConversion` that detects downsizing implicit conversions to range types (e.g., `int -> range[0..255]` or `range[1..256] -> range[0..255]`) that could cause runtime panics. Safe conversions like `range[0..255] -> range[0..65535]` and explicit casts do not trigger warnings. `int` to `Natural` and `Positive` conversions do not trigger warnings, which can be enabled with `--warning:systemRangeConversion`.
 
+- Procedure compatibility also checks the backend representation of the
+parameter and result types, not just their source-level shape. Use
+`--legacy:procParamTypeBackendAliases` to restore the older behavior.
+
 ## Standard library additions and changes
 
 [//]: # "Additions:"
@@ -77,6 +81,9 @@ errors.
 - `std/re` and `std/nre` are deprecated as PCRE library is obsolete.
   Use https://github.com/nitely/nim-regex or `std/nre2`.
   See: https://github.com/nim-lang/Nim/issues/23668.
+- `std/pegs` now correctly lexes UTF-8 bytes inside bare identifier-style
+  terminals, so case-insensitive matching of non-ASCII terms (e.g. ``\i café``)
+  works without single-quoting.
 
 ## Language changes
 

compiler/ccgexprs.nim

@@ -974,9 +974,7 @@ proc cow(p: BProc; n: PNode) {.inline.} =
   if n.kind == nkHiddenAddr: cowBracket(p, n[0])
 
 template ignoreConv(e: PNode): bool =
-  let destType = e.typ.skipTypes({tyVar, tyLent, tyGenericInst, tyAlias, tySink})
-  let srcType = e[1].typ.skipTypes({tyVar, tyLent, tyGenericInst, tyAlias, tySink})
-  sameBackendTypePickyAliases(destType, srcType)
+  sameBackendTypePickyAliases(e.typ, e[1].typ)
 
 proc genAddr(p: BProc, e: PNode, d: var TLoc) =
   # careful  'addr(myptrToArray)' needs to get the ampersand:
@@ -2816,9 +2814,9 @@ proc genWasMoved(p: BProc; n: PNode) =
     #  [addrLoc(p.config, a), getTypeDesc(p.module, a.t)])
 
 proc genMove(p: BProc; n: PNode; d: var TLoc) =
-  var a: TLoc = initLocExpr(p, n[1].skipAddr, {lfEnforceDeref, lfPrepareForMutation})
   if n.len == 4:
     # generated by liftdestructors:
+    var a: TLoc = initLocExpr(p, n[1].skipAddr, {lfEnforceDeref, lfPrepareForMutation})
     var src: TLoc = initLocExpr(p, n[2])
     let destVal = rdLoc(a)
     let srcVal = rdLoc(src)
@@ -2838,29 +2836,16 @@ proc genMove(p: BProc; n: PNode; d: var TLoc) =
   else:
     if d.k == locNone: d = getTemp(p, n.typ)
     if p.config.selectedGC in {gcArc, gcAtomicArc, gcOrc, gcYrc}:
-      genAssignment(p, d, a, {})
       var op = getAttachedOp(p.module.g.graph, n.typ, attachedWasMoved)
-      if op == nil:
+      if op == nil or sfOverridden notin op.flags:
+        var a: TLoc = initLocExpr(p, n[1].skipAddr, {lfEnforceDeref, lfPrepareForMutation})
+        genAssignment(p, d, a, {})
         resetLoc(p, a)
       else:
-        var b = initLocExpr(p, newSymNode(op))
-        case skipTypes(a.t, abstractVar+{tyStatic}).kind
-        of tyOpenArray, tyVarargs: # todo fixme generated `wasMoved` hooks for
-                                   # openarrays, but it probably shouldn't?
-          let ra = rdLoc(a)
-          var s: string
-          if reifiedOpenArray(a.lode):
-            if a.t.kind in {tyVar, tyLent}:
-              s = derefField(ra, "Field0") & cArgumentSeparator & derefField(ra, "Field1")
-            else:
-              s = dotField(ra, "Field0") & cArgumentSeparator & dotField(ra, "Field1")
-          else:
-            s = ra & cArgumentSeparator & ra & "Len_0"
-          p.s(cpsStmts).addCallStmt(rdLoc(b), s)
-        else:
-          let val = if p.module.compileToCpp: rdLoc(a) else: byRefLoc(p, a)
-          p.s(cpsStmts).addCallStmt(rdLoc(b), val)
+        n[1] = makeAddr(n[1], p.module.idgen)
+        genCall(p, n, d)
     else:
+      var a: TLoc = initLocExpr(p, n[1].skipAddr, {lfEnforceDeref, lfPrepareForMutation})
       genAssignment(p, d, a, {})
       resetLoc(p, a)
 

compiler/ccgstmts.nim

@@ -230,7 +230,7 @@ proc blockLeaveActions(p: BProc, howManyTrys, howManyExcepts: int, isReturnStmt
   # Called by return and break stmts.
   # Deals with issues faced when jumping out of try/except/finally stmts.
 
-  var stack = newSeq[tuple[fin: PNode, inExcept: bool, label: Natural]](0)
+  var stack = newSeq[tuple[fin: PNode, inExcept: bool, isHidden: bool, label: Natural]](0)
 
   inc p.withinBlockLeaveActions
   for i in 1..howManyTrys:
@@ -341,9 +341,9 @@ proc genCppParamsForCtor(p: BProc; call: PNode; didGenTemp: var bool): Snippet =
           call[i][0]
         else:
           call[i]
-      if param.kind != nkBracketExpr or param.typ.kind in
+      if not param.typ.isCompileTimeOnly and (param.kind != nkBracketExpr or param.typ.kind in
         {tyRef, tyPtr, tyUncheckedArray, tyArray, tyOpenArray,
-          tyVarargs, tySequence, tyString, tyCstring, tyTuple}:
+          tyVarargs, tySequence, tyString, tyCstring, tyTuple}):
         let tempLoc = initLocExprSingleUse(p, param)
         didGenTemp = didGenTemp or tempLoc.k == locTemp
       genOtherArg(p, call, i, typ, res, argBuilder)
@@ -836,12 +836,26 @@ proc raiseExitCleanup(p: BProc, destroy: string) =
         p.s(cpsStmts).addGoto("LA" & $p.nestedTryStmts[^1].label & "_")
 
 proc finallyActions(p: BProc) =
-  if p.config.exc != excGoto and p.nestedTryStmts.len > 0 and p.nestedTryStmts[^1].inExcept:
-    # if the current try stmt have a finally block,
-    # we must execute it before reraising
-    let finallyBlock = p.nestedTryStmts[^1].fin
-    if finallyBlock != nil:
-      genSimpleBlock(p, finallyBlock[0])
+  if p.config.exc != excGoto:
+    # Walk past compiler-injected `nkHiddenTryStmt` wrappers (e.g. ARC's
+    # destructor try/finally that wraps `except T as e:` bodies) to reach
+    # the user's actual try.  We must NOT walk past a real user try whose
+    # body we are currently in, because a raise from there will be caught
+    # by that try's own except branches rather than escaping outward.
+    #
+    # If after skipping wrappers the next entry is a user try in its
+    # except branch (inExcept=true), inline its finally body before the
+    # raise propagates — without this, the C++ sibling-catch rule would
+    # cause the user's catch(...)/finally pair to be bypassed and the
+    # finally would be silently dropped.
+    for i in countdown(p.nestedTryStmts.high, 0):
+      if p.nestedTryStmts[i].isHidden:
+        continue
+      if p.nestedTryStmts[i].inExcept:
+        let finallyBlock = p.nestedTryStmts[i].fin
+        if finallyBlock != nil:
+          genSimpleBlock(p, finallyBlock[0])
+      return
 
 proc raiseInstr(p: BProc; result: var Builder) =
   if p.config.exc == excGoto:
@@ -1185,7 +1199,7 @@ proc genTryCpp(p: BProc, t: PNode, d: var TLoc) =
   lineCg(p, cpsLocals, "std::exception_ptr T$1_;$n", [etmp])
 
   let fin = if t[^1].kind == nkFinally: t[^1] else: nil
-  p.nestedTryStmts.add((fin, false, 0.Natural))
+  p.nestedTryStmts.add((fin, false, t.kind == nkHiddenTryStmt, 0.Natural))
 
   if t.kind == nkHiddenTryStmt:
     lineCg(p, cpsStmts, "try {$n", [])
@@ -1371,7 +1385,7 @@ proc genTryCppOld(p: BProc, t: PNode, d: var TLoc) =
   genLineDir(p, t)
   cgsym(p.module, "popCurrentExceptionEx")
   let fin = if t[^1].kind == nkFinally: t[^1] else: nil
-  p.nestedTryStmts.add((fin, false, 0.Natural))
+  p.nestedTryStmts.add((fin, false, t.kind == nkHiddenTryStmt, 0.Natural))
   startBlockWith(p):
     p.s(cpsStmts).add("try {\n")
   expr(p, t[0], d)
@@ -1450,7 +1464,7 @@ proc genTryGoto(p: BProc; t: PNode; d: var TLoc) =
   let lab = p.labels
   let hasExcept = t[1].kind == nkExceptBranch
   if hasExcept: inc p.withinTryWithExcept
-  p.nestedTryStmts.add((fin, false, Natural lab))
+  p.nestedTryStmts.add((fin, false, t.kind == nkHiddenTryStmt, Natural lab))
 
   p.flags.incl nimErrorFlagAccessed
 
@@ -1656,7 +1670,7 @@ proc genTrySetjmp(p: BProc, t: PNode, d: var TLoc) =
     initElifBranch(p.s(cpsStmts), nonQuirkyIf, removeSinglePar(
       cOp(Equal, dotField(safePoint, "status"), cIntValue(0))))
   let fin = if t[^1].kind == nkFinally: t[^1] else: nil
-  p.nestedTryStmts.add((fin, quirkyExceptions, 0.Natural))
+  p.nestedTryStmts.add((fin, quirkyExceptions, t.kind == nkHiddenTryStmt, 0.Natural))
   expr(p, t[0], d)
   var quirkyIf = default(IfBuilder)
   var quirkyScope = default(ScopeBuilder)

compiler/cgendata.nim

@@ -75,10 +75,13 @@ type
     flags*: set[TCProcFlag]
     lastLineInfo*: TLineInfo  # to avoid generating excessive 'nimln' statements
     currLineInfo*: TLineInfo  # AST codegen will make this superfluous
-    nestedTryStmts*: seq[tuple[fin: PNode, inExcept: bool, label: Natural]]
+    nestedTryStmts*: seq[tuple[fin: PNode, inExcept: bool, isHidden: bool, label: Natural]]
                               # in how many nested try statements we are
                               # (the vars must be volatile then)
-                              # bool is true when are in the except part of a try block
+                              # `inExcept` is true when we are in the except part of a try block.
+                              # `isHidden` is true for compiler-injected `nkHiddenTryStmt` wrappers
+                              # (e.g. ARC's destructor try/finally around `except T as e:` bodies);
+                              # finallyActions walks past such wrappers to reach the user's try.
     finallySafePoints*: seq[Rope]  # For correctly cleaning up exceptions when
                                    # using return in finally statements
     labels*: Natural          # for generating unique labels in the C proc

compiler/commands.nim

@@ -930,7 +930,7 @@ proc processSwitch*(switch, arg: string, pass: TCmdLinePass, info: TLineInfo;
       if m.len == 0:
         localError(conf, info, "Cannot resolve filename: " & arg)
       else:
-        conf.implicitImports.add m
+        conf.implicitImports.add(if arg.startsWith(stdPrefix): arg else: m)
   of "include":
     expectArg(conf, switch, arg, pass, info)
     if pass in {passCmd2, passPP}:

compiler/deps.nim

@@ -488,10 +488,19 @@ proc generateBuildFile(c: DepContext): string =
   let exeFile = changeFileExt(c.nodes[0].files[0].nimFile, ExeExt)
   b.addTree "do"
   b.addIdent "nim_nifc"
-  # Input: .nim file (expanded as argument) and .nif file (dependency)
+  # Input: .nim file (expanded as argument)
   b.addTree "input"
   b.addStrLit mainNif
   b.endTree()
+  # Also depend on the semmed .nif files of the main module and all its
+  # dependencies. nifmake's topological sort orders nodes by depth; without
+  # these inputs the nim_nifc node sits at depth 1 (no recognized inputs)
+  # alongside the nifler nodes and runs *before* the nim_m steps that
+  # produce the .nif files it needs to read.
+  for node in c.nodes:
+    b.addTree "input"
+    b.addStrLit c.semmedFile(node.files[0])
+    b.endTree()
   b.addTree "output"
   b.addStrLit exeFile
   b.endTree()

compiler/importer.nim

@@ -13,7 +13,7 @@ import
   ast, msgs, options, idents, lookups,
   semdata, modulepaths, sigmatch, lineinfos,
   modulegraphs, wordrecg
-from std/strutils import `%`, startsWith
+from std/strutils import `%`, startsWith, replace
 from std/sequtils import addUnique
 import std/[sets, tables, intsets]
 
@@ -304,9 +304,9 @@ proc myImportModule(c: PContext, n: var PNode, importStmtResult: PNode): PSym =
       var prefix = ""
       if realModule.constraint != nil: prefix = realModule.constraint.strVal & "; "
       message(c.config, n.info, warnDeprecated, prefix & realModule.name.s & " is deprecated")
-    let moduleName = getModuleName(c.config, n)
-    if belongsToStdlib(c.graph, result) and not startsWith(moduleName, stdPrefix) and
-        not startsWith(moduleName, "system/") and not startsWith(moduleName, "packages/"):
+    let moduleNameNorm = getModuleName(c.config, n).replace("\\", "/")
+    if belongsToStdlib(c.graph, result) and not startsWith(moduleNameNorm, stdPrefix) and
+        not startsWith(moduleNameNorm, "system/") and not startsWith(moduleNameNorm, "packages/"):
       message(c.config, n.info, warnStdPrefix, realModule.name.s)
 
     proc suggestMod(n: PNode; s: PSym) =

compiler/lexer.nim

@@ -1349,7 +1349,7 @@ proc rawGetTok*(L: var Lexer, tok: var Token) =
           lexMessage(L, errGenerated, "invalid token: no whitespace between number and identifier")
     of '-':
       if L.buf[L.bufpos+1] in {'0'..'9'} and
-          (L.bufpos-1 == 0 or L.buf[L.bufpos-1] in UnaryMinusWhitelist):
+          (L.bufpos == 0 or L.buf[L.bufpos-1] in UnaryMinusWhitelist):
         # x)-23 # binary minus
         # ,-23  # unary minus
         # \n-78 # unary minus? Yes.

compiler/options.nim

@@ -259,6 +259,9 @@ type
       ## Old transformation for closures in JS backend
     noPanicOnExcept
       ## don't panic on bare except
+    procParamTypeBackendAliases
+      ## Keep the old proc type compatibility rules that ignore backend
+      ## c type aliases.
 
   SymbolFilesOption* = enum
     disabledSf, writeOnlySf, readOnlySf, v2Sf, stressTest

compiler/semdata.nim

@@ -637,6 +637,11 @@ proc renderNotLValue*(n: PNode): string =
   elif n.kind in {nkHiddenStdConv, nkHiddenSubConv} and n.len == 2:
     result = typeToString(n.typ.skipTypes(abstractVar)) & "(" & result & ")"
 
+proc isSsoStringIndex*(conf: ConfigRef; n: PNode): bool =
+  result = conf.usesSso() and n.kind == nkBracketExpr and n.len >= 1 and
+      n[0].typ != nil and
+      n[0].typ.skipTypes(abstractVar + abstractInst - {tyTypeDesc}).kind == tyString
+
 proc isAssignable(c: PContext, n: PNode): TAssignableResult =
   result = parampatterns.isAssignable(c.p.owner, n)
 

compiler/semexprs.nim

@@ -578,7 +578,14 @@ proc isOpImpl(c: PContext, n: PNode, flags: TExprFlags): PNode =
     if efExplain in flags:
       m.diagnostics = @[]
       m.diagnosticsEnabled = true
-    res = typeRel(m, t2, t1) >= isSubtype # isNone
+    let rel = typeRel(m, t2, t1)
+    res = rel >= isSubtype # isNone
+    if res and rel == isEqual and
+        not compareTypes(t1, t2,
+                         flags = {ExactTypeDescValues,
+                                  PickyCAliases,
+                                  PickyBackendAliases}):
+      res = false
     # `res = sameType(t1, t2)` would be wrong, e.g. for `int is (int|float)`
 
   result = newIntNode(nkIntLit, ord(res))
@@ -652,6 +659,9 @@ proc overloadedCallOpr(c: PContext, n: PNode): PNode =
     result = semExpr(c, result, flags = {efNoUndeclared})
 
 proc changeType(c: PContext; n: PNode, newType: PType, check: bool) =
+  template isViewTarget(t: PType): bool =
+    t.skipTypes({tyGenericInst, tyAlias, tySink}).kind in {tyVar, tyLent}
+
   case n.kind
   of nkCurly:
     for i in 0..<n.len:
@@ -680,12 +690,15 @@ proc changeType(c: PContext; n: PNode, newType: PType, check: bool) =
           if f == nil:
             globalError(c.config, m.info, "unknown identifier: " & m.sym.name.s)
             return
-          changeType(c, n[i][1], f.typ, check)
+          if not isViewTarget(f.typ):
+            changeType(c, n[i][1], f.typ, check)
         else:
-          changeType(c, n[i][1], tup[i], check)
+          if not isViewTarget(tup[i]):
+            changeType(c, n[i][1], tup[i], check)
     else:
       for i in 0..<n.len:
-        changeType(c, n[i], tup[i], check)
+        if not isViewTarget(tup[i]):
+          changeType(c, n[i], tup[i], check)
         when false:
           var m = n[i]
           var a = newNodeIT(nkExprColonExpr, m.info, newType[i])
@@ -708,6 +721,7 @@ proc changeType(c: PContext; n: PNode, newType: PType, check: bool) =
         localError(c.config, n.info, "cannot convert '" & n.sym.name.s &
                                          "' to '" & typeNameAndDesc(newType) & "'")
   else: discard
+
   n.typ = newType
 
 proc arrayConstrType(c: PContext, n: PNode): PType =

compiler/seminst.nim

@@ -81,7 +81,8 @@ proc sameInstantiation(a, b: TInstantiation): bool =
       if not compareTypes(a.concreteTypes[i], b.concreteTypes[i],
                           flags = {ExactTypeDescValues,
                                    ExactGcSafety,
-                                   PickyCAliases}): return
+                                   PickyCAliases,
+                                   PickyBackendAliases}): return
     result = true
   else:
     result = false

compiler/semmagic.nim

@@ -65,7 +65,7 @@ proc semTypeOf(c: PContext; n: PNode): PNode =
       t.incl tfNonConstExpr
     else:
       t = base
-  result.typ = makeTypeDesc(c, decayTypeOfView(c, t))
+  result.typ = makeTypeDesc(c, t)
 
 type
   SemAsgnMode = enum asgnNormal, noOverloadedSubscript, noOverloadedAsgn
@@ -248,10 +248,13 @@ proc evalTypeTrait(c: PContext; traitCall: PNode, operand: PType, context: PSym)
     assert operand.kind == tyTuple, $operand.kind
     result = newIntNodeT(toInt128(operand.len), traitCall, c.idgen, c.graph)
   of "distinctBase":
-    var arg = operand.skipTypes({tyGenericInst})
+    var arg = operand.skipTypes(skippedTypes)
     let rec = semConstExpr(c, traitCall[2]).intVal != 0
-    while arg.kind == tyDistinct:
-      arg = arg.base.skipTypes(skippedTypes + {tyGenericInst})
+    while true:
+      let distinctArg = arg.skipTypes(skippedTypes + {tyGenericInst})
+      if distinctArg.kind != tyDistinct:
+        break
+      arg = distinctArg.base.skipTypes(skippedTypes)
       if not rec: break
     result = getTypeDescNode(c, arg, operand.owner, traitCall.info)
   of "rangeBase":

compiler/semobjconstr.nim

@@ -486,6 +486,11 @@ proc semObjConstr(c: PContext, n: PNode, flags: TExprFlags; expectedType: PType
       # we have to watch out, there are also 'owned proc' types that can be used
       # multiple times as long as they don't have closures.
       result.typ.incl tfHasOwned
+  if t.kind == tyForward and efDetermineType in flags:
+    # a forward object type does not error during determine-type analysis;
+    # it now stays unresolved long enough for the existing delayed field-default pass to resolve it after the type section finishes.
+    result.typ = t
+    return result
   if t.kind != tyObject:
     return localErrorNode(c, result, if t.kind != tyGenericBody:
       "object constructor needs an object type".dup(addTypeNodeDeclaredLoc(c.config, t))

compiler/sempass2.nim

@@ -809,6 +809,10 @@ proc trackOperandForIndirectCall(tracked: PEffects, n: PNode, formals: PType; ar
         markSideEffect(tracked, a, n.info)
   let paramType = if formals != nil and argIndex < formals.signatureLen: formals[argIndex] else: nil
   if paramType != nil and paramType.kind in {tyVar}:
+    let arg = n.skipAddr()
+    if isSsoStringIndex(tracked.config, arg):
+      localError(tracked.config, arg.info,
+        "expression '$1' is immutable, not 'var'" % renderNotLValue(arg))
     invalidateFacts(tracked.guards, n)
     if n.kind == nkSym and isLocalSym(tracked, n.sym):
       makeVolatile(tracked, n.sym)

compiler/semstmts.nim

@@ -815,14 +815,6 @@ proc makeVarTupleSection(c: PContext, n, a, def: PNode, typ: PType, symkind: TSy
       lastDef[^1] = val
     result.add(lastDef)
 
-proc materializeDirectView(n: PNode): PNode =
-  let t = n.typ.skipTypes({tyGenericInst, tyAlias, tySink, tyOwned})
-  if t.kind in {tyVar, tyLent}:
-    result = newNodeIT(nkHiddenDeref, n.info, t.elementType)
-    result.add n
-  else:
-    result = n
-
 proc semVarOrLet(c: PContext, n: PNode, symkind: TSymKind): PNode =
   var b: PNode
   result = copyNode(n)
@@ -889,10 +881,6 @@ proc semVarOrLet(c: PContext, n: PNode, symkind: TSymKind): PNode =
           #changeType(def.skipConv, typ, check=true)
       else:
         typ = def.typ.skipTypes({tyStatic, tySink}).skipIntLit(c.idgen)
-        let directTyp = typ.skipTypes({tyGenericInst, tyAlias, tySink, tyOwned})
-        if directTyp.kind in {tyVar, tyLent}:
-          def = materializeDirectView(def)
-          typ = def.typ.skipTypes({tyStatic, tySink}).skipIntLit(c.idgen)
         if typ.kind in tyUserTypeClasses and typ.isResolvedUserTypeClass:
           typ = typ.last
         if hasEmpty(typ):
@@ -920,8 +908,7 @@ proc semVarOrLet(c: PContext, n: PNode, symkind: TSymKind): PNode =
 
     if c.matchedConcept != nil:
       typFlags.incl taConcept
-    if a.kind != nkVarTuple:
-      typeAllowedCheck(c, a.info, typ, symkind, typFlags)
+    typeAllowedCheck(c, a.info, typ, symkind, typFlags)
 
     var tup = skipTypes(typ, {tyGenericInst, tyAlias, tySink})
     if a.kind == nkVarTuple:

compiler/semtypes.nim

@@ -370,6 +370,7 @@ proc semFieldDefault(c: PContext; owner, expectedType: PType; field: PNode): PTy
       propagateToOwner(owner, result)
 
 proc semDelayedFieldDefault(c: PContext; owner, expectedType: PType; field: PNode) =
+  resetSemFlag(field[^1])
   fitDefaultNode(c, field[^1], expectedType)
   propagateToOwner(owner, field[^1].typ.skipIntLit(c.idgen))
 
@@ -1879,38 +1880,6 @@ proc fixupTypeOf(c: PContext, prev: PType, typ: PType) =
     if prev.kind != tyGenericBody:
       assignType(prev, result)
 
-proc decayTypeOfView(c: PContext, typ: PType): PType =
-  if typ == nil: return nil
-  let t = typ.skipTypes({tyGenericInst, tyAlias, tySink})
-  case t.kind
-  of tyVar, tyLent:
-    result = decayTypeOfView(c, t.elementType)
-  of tyTuple:
-    var changed = false
-    var kids = newSeq[PType](t.len)
-    for i in 0..<t.len:
-      kids[i] = decayTypeOfView(c, t[i])
-      if kids[i] != t[i]: changed = true
-    if changed:
-      result = copyType(t, c.idgen, t.owner)
-      for i in 0..<kids.len:
-        result[i] = kids[i]
-      if t.n != nil:
-        result.n = copyNode(t.n)
-        for it in t.n:
-          if it.kind == nkSym and it.sym.kind == skField:
-            let field = copySym(it.sym, c.idgen)
-            field.ast = it.sym.ast
-            if field.position >= 0 and field.position < kids.len:
-              field.typ = kids[field.position]
-            result.n.add newSymNode(field, it.info)
-          else:
-            result.n.add copyTree(it)
-    else:
-      result = typ
-  else:
-    result = typ
-
 proc semTypeExpr(c: PContext, n: PNode; prev: PType): PType =
   var n = semExprWithType(c, n, {efDetermineType})
   if n.typ.kind == tyTypeDesc:
@@ -2110,7 +2079,6 @@ proc semTypeOf(c: PContext; n: PNode; prev: PType): PType =
       result.incl tfNonConstExpr
     else:
       result = base
-  result = decayTypeOfView(c, result)
   fixupTypeOf(c, prev, result)
 
 proc semTypeOf2(c: PContext; n: PNode; prev: PType): PType =
@@ -2136,7 +2104,6 @@ proc semTypeOf2(c: PContext; n: PNode; prev: PType): PType =
       result.incl tfNonConstExpr
     else:
       result = base
-  result = decayTypeOfView(c, result)
   fixupTypeOf(c, prev, result)
 
 proc semTypeIdent(c: PContext, n: PNode): PSym =

compiler/semtypinst.nim

@@ -52,7 +52,8 @@ proc searchInstTypes*(g: ModuleGraph; key: PType): PType =
       for j in FirstGenericParamAt..<key.kidsLen:
         # XXX sameType is not really correct for nested generics?
         if not compareTypes(inst[j], key[j],
-                            flags = {ExactGenericParams, PickyCAliases}):
+                            flags = {ExactGenericParams, PickyCAliases,
+                                     PickyBackendAliases}):
           break matchType
 
       return inst

compiler/sigmatch.nim

@@ -15,8 +15,6 @@ import
   magicsys, idents, lexer, options, parampatterns, trees,
   linter, lineinfos, lowerings, modulegraphs, concepts, layeredtable
 
-import typeallowed
-
 import std/[intsets, strutils, tables]
 
 when defined(nimPreviewSlimSystem):
@@ -125,58 +123,6 @@ proc initCandidate*(ctx: PContext, callee: PType): TCandidate =
   result.calleeSym = nil
   result.bindings = initLayeredTypeMap()
 
-proc materializeTupleViewType(t: PType; idgen: IdGenerator): PType =
-  case t.kind
-  of tyVar, tyLent:
-    result = materializeTupleViewType(t.elementType, idgen)
-  of tyTuple:
-    if classifyViewType(t) == noView:
-      result = t
-    else:
-      result = copyType(t, idgen, t.owner)
-      for i in 0..<t.len:
-        result[i] = materializeTupleViewType(t[i], idgen)
-      if t.n != nil:
-        result.n = copyNode(t.n)
-        for it in t.n:
-          if it.kind == nkSym and it.sym.kind == skField:
-            let field = copySym(it.sym, idgen)
-            field.ast = it.sym.ast
-            if field.position >= 0 and field.position < result.len:
-              field.typ = result[field.position]
-            result.n.add newSymNode(field, it.info)
-          else:
-            result.n.add copyTree(it)
-  else:
-    result = t
-
-proc materializeTupleViewArg(c: PContext; targetType: PType; arg: PNode): PNode =
-  let targetTuple = targetType.skipTypes({tyGenericInst, tyAlias, tySink, tyDistinct, tyInferred})
-  var tupleArg = arg
-  var prefix: PNode = nil
-  if targetTuple.len > 1 and arg.kind notin {nkHiddenAddr, nkSym}:
-    prefix = evalOnce(c.graph, arg, c.idgen, getCurrOwner(c))
-    tupleArg = prefix[^1]
-
-  let tupleConstr = newNodeIT(nkTupleConstr, arg.info, targetType)
-  for i in 0..<targetTuple.len:
-    let targetField = targetTuple[i]
-    var field = newTupleAccess(c.graph, tupleArg, i)
-    let sourceField = field.typ.skipTypes({tyGenericInst, tyAlias, tySink, tyDistinct, tyInferred})
-    if sourceField.kind in {tyVar, tyLent}:
-      field = newDeref(field)
-    elif targetField.kind == tyTuple and classifyViewType(sourceField) != noView:
-      field = materializeTupleViewArg(c, targetField, field)
-    tupleConstr.add field
-
-  if prefix == nil:
-    result = tupleConstr
-  else:
-    result = newNodeIT(nkStmtListExpr, arg.info, targetType)
-    for i in 0..<(prefix.len - 1):
-      result.add prefix[i]
-    result.add tupleConstr
-
 proc put(c: var TCandidate, key, val: PType) {.inline.} =
   ## Given: proc foo[T](x: T); foo(4)
   ## key: 'T'
@@ -189,12 +135,7 @@ proc put(c: var TCandidate, key, val: PType) {.inline.} =
         writeStackTrace()
     if c.c.module.name.s == "temp3":
       echo "binding ", key, " -> ", val
-
-  let normalized = val.skipIntLit(c.c.idgen)
-  if normalized.kind == tyTuple and classifyViewType(normalized) != noView:
-    put(c.bindings, key, materializeTupleViewType(normalized, c.c.idgen))
-  else:
-    put(c.bindings, key, normalized)
+  put(c.bindings, key, val.skipIntLit(c.c.idgen))
 
 proc typeRel*(c: var TCandidate, f, aOrig: PType,
               flags: TTypeRelFlags = {}): TTypeRelation
@@ -843,6 +784,17 @@ proc procParamTypeRel(c: var TCandidate; f, a: PType): TTypeRelation =
     # if f is metatype.
     result = typeRel(c, f, a)
 
+  if result == isEqual and
+      procParamTypeBackendAliases notin c.c.config.legacyFeatures:
+    # Ensure types that are semantically equal also match at the backend level.
+    # E.g. reject assigning proc(csize_t) to proc(uint) since these map to
+    # different C types (size_t vs unsigned long long).
+    let fCheck = concreteType(c, f)
+    let aCheck = concreteType(c, a)
+    if fCheck != nil and aCheck != nil and
+        not sameBackendTypePickyAliases(fCheck, aCheck):
+      result = isNone
+
   if result <= isSubrange or inconsistentVarTypes(f, a):
     result = isNone
 
@@ -2259,16 +2211,7 @@ proc implicitConv(kind: TNodeKind, f: PType, arg: PNode, m: TCandidate,
 
   if result.typ == nil: internalError(c.graph.config, arg.info, "implicitConv")
   result.add c.graph.emptyNode
-  let targetTuple = result.typ.skipTypes({tyVar, tyGenericInst, tyAlias, tySink, tyDistinct, tyInferred})
-  let sourceTuple =
-    if arg.typ != nil:
-      arg.typ.skipTypes({tyGenericInst, tyAlias, tySink, tyDistinct, tyInferred})
-    else:
-      nil
-  if sourceTuple != nil and sourceTuple.kind == tyTuple and targetTuple.kind == tyTuple and
-      classifyViewType(arg.typ) != noView and classifyViewType(result.typ) == noView:
-    result.add materializeTupleViewArg(c, targetTuple, arg)
-  elif arg.typ != nil and arg.typ.kind == tyLent:
+  if arg.typ != nil and arg.typ.kind == tyLent:
     let a = newNodeIT(nkHiddenDeref, arg.info, arg.typ.elementType)
     a.add arg
     result.add a

compiler/spawn.nim

@@ -10,7 +10,7 @@
 ## This module implements threadpool's ``spawn``.
 
 import ast, types, idents, magicsys, msgs, options, modulegraphs,
-  lowerings, liftdestructors, renderer
+  lowerings, liftdestructors, renderer, trees
 from trees import getMagic, getRoot
 
 proc callProc(a: PNode): PNode =
@@ -53,6 +53,24 @@ proc typeNeedsNoDeepCopy(t: PType): bool =
   if t.kind in {tyVar, tyLent, tySequence}: t = t.elementType
   result = not containsGarbageCollectedRef(t)
 
+proc newSpawnMoveStmt(g: ModuleGraph; idgen: IdGenerator; le, ri: PNode): PNode =
+  let op = getAttachedOp(g, ri.typ.skipTypes({tyGenericInst, tyAlias, tyVar, tySink}), attachedWasMoved)
+  if op != nil and sfOverridden in op.flags:
+    result = newNodeI(nkStmtList, le.info)
+    result.add newFastAsgnStmt(le, ri)
+
+    let wasMovedCall = newNodeI(nkCall, ri.info)
+    wasMovedCall.add newSymNode(op)
+    
+    if op.typ != nil and op.typ.signatureLen > 1 and op.typ.firstParamType.kind != tyVar:
+      wasMovedCall.add ri.skipAddr
+    else:
+      wasMovedCall.add makeAddr(ri.skipAddr, idgen)
+    
+    result.add wasMovedCall
+  else:
+    result = newFastMoveStmt(g, le, ri)
+
 proc addLocalVar(g: ModuleGraph; varSection, varInit: PNode; idgen: IdGenerator; owner: PSym; typ: PType;
                  v: PNode; useShallowCopy=false): PSym =
   result = newSym(skTemp, getIdent(g.cache, genPrefix), idgen, owner, varSection.info,
@@ -68,10 +86,10 @@ proc addLocalVar(g: ModuleGraph; varSection, varInit: PNode; idgen: IdGenerator;
   if varInit != nil:
     if g.config.selectedGC in {gcArc, gcOrc, gcAtomicArc, gcYrc}:
       # inject destructors pass will do its own analysis
-      varInit.add newFastMoveStmt(g, newSymNode(result), v)
+      varInit.add newSpawnMoveStmt(g, idgen, newSymNode(result), v)
     else:
       if useShallowCopy and typeNeedsNoDeepCopy(typ) or optTinyRtti in g.config.globalOptions:
-        varInit.add newFastMoveStmt(g, newSymNode(result), v)
+        varInit.add newSpawnMoveStmt(g, idgen, newSymNode(result), v)
       else:
         let deepCopyCall = newNodeI(nkCall, varInit.info, 3)
         deepCopyCall[0] = newSymNode(getSysMagic(g, varSection.info, "deepCopy", mDeepCopy))

compiler/types.nim

@@ -897,7 +897,11 @@ proc sameTypeAux(x, y: PType, c: var TSameTypeClosure): bool =
     c.flags = oldFlags
 
   if x == y: return true
-  let aliasSkipSet = maybeSkipRange({tyAlias})
+  let aliasSkipSet = maybeSkipRange(
+    if PickyBackendAliases in c.flags:
+      {tyInferred}
+    else:
+      {tyAlias, tyInferred})
   var a = skipTypes(x, aliasSkipSet)
   while a.kind == tyUserTypeClass and tfResolved in a.flags:
     a = skipTypes(a.last, aliasSkipSet)
@@ -1070,6 +1074,8 @@ proc sameBackendTypeIgnoreRange*(x, y: PType): bool =
   result = sameTypeAux(x, y, c)
 
 proc sameBackendTypePickyAliases*(x, y: PType): bool =
+  let x = x.skipTypes({tyVar, tyLent, tySink, tyOwned})
+  let y = y.skipTypes({tyVar, tyLent, tySink, tyOwned})
   var c = initSameTypeClosure()
   c.flags.incl {IgnoreTupleFields, IgnoreRangeShallow, PickyCAliases, PickyBackendAliases}
   c.cmp = dcEqIgnoreDistinct

doc/ic.md

@@ -33,7 +33,7 @@ The text representation is particularly valuable for debugging and introspection
 Each ``.nim`` module produces its own ``.nif`` file during compilation.
 The NIF format contains:
 
-- **Header** - Version information (e.g., `(.nif26)`)
+- **Header** - Version information (e.g., `(.nif27)`)
 - **Dependencies** - List of source files and dependencies
 - **Interface** - Exported symbols and their indices
 - **Body** - The intermediate representation of the module's code in Lisp-like syntax

doc/manual.md

@@ -34,10 +34,10 @@ To learn how to compile Nim programs and generate documentation see
 the [Compiler User Guide](nimc.html) and the [DocGen Tools Guide](docgen.html).
 
 The language constructs are explained using an extended BNF, in which `(a)*`
-means 0 or more `a`'s, `a+` means 1 or more `a`'s, and `(a)?` means an
+means 0 or more *a*'s, `a+` means 1 or more *a*'s, and `(a)?` means an
 optional *a*. Parentheses may be used to group elements.
 
-`&` is the lookahead operator; `&a` means that an `a` is expected but
+`&` is the lookahead operator; `&a` means that an *a* is expected but
 not consumed. It will be consumed in the following rule.
 
 The `|`, `/` symbols are used to mark alternatives and have the lowest
@@ -1024,6 +1024,9 @@ These are the major type classes:
 * procedural type
 * generic type
 
+The compiler's internal type zoo is richer than this summary suggests:
+some types that are structurally equal still differ in backend representation.
+
 
 Ordinal types
 -------------
@@ -2174,6 +2177,10 @@ Procedural type
 A procedural type is internally a pointer to a procedure. `nil` is
 an allowed value for a variable of a procedural type.
 
+Procedure compatibility also checks the backend representation of the
+parameter and result types, not just their source-level shape. Use
+`--legacy:procParamTypeBackendAliases` to restore the older behavior.
+
 Examples:
 
   ```nim
@@ -8867,7 +8874,7 @@ Byref pragma
 The `byref` pragma can be applied to an object or tuple type or a proc param.
 When applied to a type it instructs the compiler to pass the type by reference
 (hidden pointer) to procs. When applied to a param it will take precedence, even
-if the the type was marked as `bycopy`. When an `importc` type has a `byref` pragma or
+if the type was marked as `bycopy`. When an `importc` type has a `byref` pragma or
 parameters are marked as `byref` in an `importc` proc, these params translate to pointers.
 When an `importcpp` type has a `byref` pragma, these params translate to
 C++ references `&`.

doc/tut1.md

@@ -1144,7 +1144,7 @@ there is a difference between the `$` and `repr` outputs:
   echo myCharacter, ":", repr(myCharacter)
   # --> n:'n'
   echo myString, ":", repr(myString)
-  # --> nim:0x10fa8c050"nim"
+  # --> nim:"nim"
   echo myInteger, ":", repr(myInteger)
   # --> 42:42
   echo myFloat, ":", repr(myFloat)

koch.nim

@@ -16,11 +16,11 @@ const
   ChecksumsStableCommit = "0b8e46379c5bc1bf73d8b3011908389c60fb9b98" # 2.0.1
   SatStableCommit = "e63eaea8baf00bed8bcd5a29ffd8823abb265b39"
 
-  NimonyStableCommit = "c189ef438598878b2f02f6a2ff91d08febafc04b" # unversioned \
+  NimonyStableCommit = "750aa47f2139fe5ad69f04b44428b752011fe873" # unversioned \
     # Note that Nimony uses Nim as a git submodule but we don't want to install
     # Nimony's dependency to Nim as we are Nim. So a `git clone` without --recursive
     # is **required** here.
-    # Commit from 2026-04-27
+    # Commit from 2026-05-05
 
   # examples of possible values for fusion: #head, #ea82b54, 1.2.3
   FusionStableHash = "#562467452b32cb7a97410ea177f083e6d8405734"

lib/pure/asynchttpserver.nim

@@ -153,7 +153,7 @@ proc parseProtocol(protocol: string): tuple[orig: string, major, minor: int] =
         protocol)
   result.orig = protocol
   i.inc protocol.parseSaturatedNatural(result.major, i)
-  i.inc # Skip .
+  if i < protocol.len: inc i # Skip .
   i.inc protocol.parseSaturatedNatural(result.minor, i)
 
 proc sendStatus(client: AsyncSocket, status: string): Future[void] =

lib/pure/collections/critbits.nim

@@ -495,13 +495,16 @@ func `$`*[T](c: CritBitTree[T]): string =
       const avgItemLen = 16
     result = newStringOfCap(c.count * avgItemLen)
     result.add("{")
+    var first = true
     when T is void:
       for key in keys(c):
-        if result.len > 1: result.add(", ")
+        if first: first = false
+        else: result.add(", ")
         result.addQuoted(key)
     else:
       for key, val in pairs(c):
-        if result.len > 1: result.add(", ")
+        if first: first = false
+        else: result.add(", ")
         result.addQuoted(key)
         result.add(": ")
         result.addQuoted(val)

lib/pure/collections/deques.nim

@@ -454,8 +454,10 @@ proc `$`*[T](deq: Deque[T]): string =
     assert $a == "[10, 20, 30]"
 
   result = "["
+  var first = true
   for x in deq:
-    if result.len > 1: result.add(", ")
+    if first: first = false
+    else: result.add(", ")
     result.addQuoted(x)
   result.add("]")
 

lib/pure/collections/heapqueue.nim

@@ -260,7 +260,9 @@ proc `$`*[T](heap: HeapQueue[T]): string =
     assert $heap == "[1, 2]"
 
   result = "["
+  var first = true
   for x in heap.data:
-    if result.len > 1: result.add(", ")
+    if first: first = false
+    else: result.add(", ")
     result.addQuoted(x)
   result.add("]")

lib/pure/collections/lists.nim

@@ -304,8 +304,10 @@ proc `$`*[T](L: SomeLinkedCollection[T]): string =
     assert $a == "[1, 2, 3, 4]"
 
   result = "["
+  var first = true
   for x in nodes(L):
-    if result.len > 1: result.add(", ")
+    if first: first = false
+    else: result.add(", ")
     result.addQuoted(x.value)
   result.add("]")
 

lib/pure/collections/tables.nim

@@ -739,7 +739,7 @@ template withValue*[A, B](t: Table[A, B], key: A,
     discard
 
 
-iterator pairs*[A, B](t: Table[A, B]): (lent A, lent B) =
+iterator pairs*[A, B](t: Table[A, B]): (A, B) =
   ## Iterates over any `(key, value)` pair in the table `t`.
   ##
   ## See also:
@@ -1201,7 +1201,7 @@ proc `==`*[A, B](s, t: TableRef[A, B]): bool =
 
 
 
-iterator pairs*[A, B](t: TableRef[A, B]): (lent A, lent B) =
+iterator pairs*[A, B](t: TableRef[A, B]): (A, B) =
   ## Iterates over any `(key, value)` pair in the table `t`.
   ##
   ## See also:
@@ -1789,7 +1789,7 @@ proc `==`*[A, B](s, t: OrderedTable[A, B]): bool =
 
 
 
-iterator pairs*[A, B](t: OrderedTable[A, B]): (lent A, lent B) =
+iterator pairs*[A, B](t: OrderedTable[A, B]): (A, B) =
   ## Iterates over any `(key, value)` pair in the table `t` in insertion
   ## order.
   ##
@@ -2212,7 +2212,7 @@ proc `==`*[A, B](s, t: OrderedTableRef[A, B]): bool =
 
 
 
-iterator pairs*[A, B](t: OrderedTableRef[A, B]): (lent A, lent B) =
+iterator pairs*[A, B](t: OrderedTableRef[A, B]): (A, B) =
   ## Iterates over any `(key, value)` pair in the table `t` in insertion
   ## order.
   ##
@@ -2622,7 +2622,7 @@ proc `==`*[A](s, t: CountTable[A]): bool =
   equalsImpl(s, t)
 
 
-iterator pairs*[A](t: CountTable[A]): (lent A, int) =
+iterator pairs*[A](t: CountTable[A]): (A, int) =
   ## Iterates over any `(key, value)` pair in the table `t`.
   ##
   ## See also:
@@ -2899,7 +2899,7 @@ proc `==`*[A](s, t: CountTableRef[A]): bool =
   else: result = s[] == t[]
 
 
-iterator pairs*[A](t: CountTableRef[A]): (lent A, int) =
+iterator pairs*[A](t: CountTableRef[A]): (A, int) =
   ## Iterates over any `(key, value)` pair in the table `t`.
   ##
   ## See also:

lib/pure/pegs.nim

@@ -1668,7 +1668,10 @@ func getSymbol(c: var PegLexer, tok: var Token) =
   while pos < c.buf.len:
     add(tok.literal, c.buf[pos])
     inc(pos)
-    if pos < c.buf.len and c.buf[pos] notin strutils.IdentChars: break
+    if pos < c.buf.len:
+      let ch = c.buf[pos]
+      # Keep non-ASCII bytes so UTF-8 terminals reach the rune-aware matchers.
+      if ch notin strutils.IdentChars and ord(ch) < 0x80: break
   c.bufpos = pos
   tok.kind = tkIdentifier
 

lib/pure/strtabs.nim

@@ -380,8 +380,10 @@ proc `$`*(t: StringTableRef): string {.rtlFunc, extern: "nstDollar".} =
     result = "{:}"
   else:
     result = "{"
+    var first = true
     for key, val in pairs(t):
-      if result.len > 1: result.add(", ")
+      if first: first = false
+      else: result.add(", ")
       result.add(key)
       result.add(": ")
       result.add(val)

lib/system.nim

@@ -166,7 +166,7 @@ proc wasMoved*[T](obj: var T) {.magic: "WasMoved", noSideEffect.}
   ## it was "moved" and to signify its destructor should do nothing and
   ## ideally be optimized away.
 
-proc move*[T](x: var T): T {.magic: "Move", noSideEffect.} =
+proc move*[T](x: var T): T {.magic: "Move", noSideEffect, nodestroy.} =
   result = x
   {.cast(raises: []), cast(tags: []).}:
     `=wasMoved`(x)
@@ -2694,7 +2694,9 @@ when hasAlloc or defined(nimscript):
     setLen(x, xl+item.len)
     var j = xl-1
     while j >= i:
-      when defined(gcArc) or defined(gcOrc) or defined(gcYrc) or defined(gcAtomicArc):
+      when defined(nimsso):
+        x[j+item.len] = x[j]
+      elif defined(gcArc) or defined(gcOrc) or defined(gcYrc) or defined(gcAtomicArc):
         x[j+item.len] = move x[j]
       else:
         shallowCopy(x[j+item.len], x[j])

lib/system/alloc.nim

@@ -691,7 +691,7 @@ proc getBigChunk(a: var MemRegion, size: int): PBigChunk =
     removeChunkFromMatrix2(a, result, fl, sl)
     if result.size >= size + PageSize:
       splitChunk(a, result, size)
-  # set 'used' to to true:
+  # set 'used' to true:
   result.prevSize = 1
   track("setUsedToFalse", addr result.size, sizeof(int))
   sysAssert result.owner == addr a, "getBigChunk: No owner set!"
@@ -708,7 +708,7 @@ proc getHugeChunk(a: var MemRegion; size: int): PBigChunk =
   result.next = nil
   result.prev = nil
   result.size = size
-  # set 'used' to to true:
+  # set 'used' to true:
   result.prevSize = 1
   result.owner = addr a
   incl(a, a.chunkStarts, pageIndex(result))

lib/system/gc_common.nim

@@ -143,7 +143,7 @@ when nimCoroutines:
 
   proc find(first: var GcStack, bottom: pointer): ptr GcStack =
     ## Find stack struct based on bottom pointer. If `bottom` is nil then main
-    ## thread stack is is returned.
+    ## thread stack is returned.
     if bottom == nil:
       return addr(gch.stack)
 

lib/system/indices.nim

@@ -59,16 +59,35 @@ template `[]=`*(s: string; i: int; val: char) = arrPut(s, i, val)
 template `^^`(s, i: untyped): untyped =
   (when i is BackwardsIndex: s.len - int(i) else: int(i))
 
-template spliceImpl(s, a, L, b: typed): untyped =
+template spliceStringImpl(s, a, L, b: typed): untyped =
   # make room for additional elements or cut:
   var shift = b.len - max(0,L)  # ignore negative slice size
   var newLen = s.len + shift
   if shift > 0:
     # enlarge:
     setLen(s, newLen)
-    for i in countdown(newLen-1, a+b.len): movingCopy(s[i], s[i-shift])
+    for i in countdown(newLen-1, a+b.len):
+      s[i] = s[i-shift]
   else:
-    for i in countup(a+b.len, newLen-1): movingCopy(s[i], s[i-shift])
+    for i in countup(a+b.len, newLen-1):
+      s[i] = s[i-shift]
+    # cut down:
+    setLen(s, newLen)
+  # fill the hole:
+  for i in 0 ..< b.len: s[a+i] = b[i]
+
+template spliceSeqImpl(s, a, L, b: typed): untyped =
+  # make room for additional elements or cut:
+  var shift = b.len - max(0,L)  # ignore negative slice size
+  var newLen = s.len + shift
+  if shift > 0:
+    # enlarge:
+    setLen(s, newLen)
+    for i in countdown(newLen-1, a+b.len):
+      movingCopy(s[i], s[i-shift])
+  else:
+    for i in countup(a+b.len, newLen-1):
+      movingCopy(s[i], s[i-shift])
     # cut down:
     setLen(s, newLen)
   # fill the hole:
@@ -102,7 +121,7 @@ proc `[]=`*[T, U: Ordinal](s: var string, x: HSlice[T, U], b: string) {.systemRa
   if L == b.len:
     for i in 0..<L: s[i+a] = b[i]
   else:
-    spliceImpl(s, a, L, b)
+    spliceStringImpl(s, a, L, b)
 
 proc `[]`*[Idx, T; U, V: Ordinal](a: array[Idx, T], x: HSlice[U, V]): seq[T] {.systemRaisesDefect.} =
   ## Slice operation for arrays.
@@ -162,4 +181,4 @@ proc `[]=`*[T; U, V: Ordinal](s: var seq[T], x: HSlice[U, V], b: openArray[T]) {
   if L == b.len:
     for i in 0 ..< L: s[i+a] = b[i]
   else:
-    spliceImpl(s, a, L, b)
+    spliceSeqImpl(s, a, L, b)

lib/system/strs_v3.nim

@@ -224,13 +224,14 @@ proc cmpStringPtrs(a, b: ptr SmallString): int {.inline.} =
         minLen - AlwaysAvail)
     if result == 0: result = aslen - bslen
     return
-  # At least one is long. Hot prefix: inlinePtr[0..AlwaysAvail-1] mirrors heap data.
-  let pfxLen = min(min(aslen, bslen), AlwaysAvail)
-  result = cmpInlineBytes(inlinePtrOf(a), inlinePtrOf(b), pfxLen)
-  if result != 0: return
+  # At least one is long. Hot prefix mirrors heap data, but only up to fullLen:
+  # shrinking can leave stale bytes in the inline cache past the logical length.
   let la = if aslen > PayloadSize: a.more.fullLen else: aslen
   let lb = if bslen > PayloadSize: b.more.fullLen else: bslen
   let minLen = min(la, lb)
+  let pfxLen = min(minLen, AlwaysAvail)
+  result = cmpInlineBytes(inlinePtrOf(a), inlinePtrOf(b), pfxLen)
+  if result != 0: return
   if minLen <= AlwaysAvail:
     result = la - lb
     return

tests/arc/t24720.nim

@@ -1,20 +0,0 @@
-discard """
-  matrix: "--mm:orc"
-  output: '''
-found entry
-'''
-"""
-
-import std/tables
-type NoCopies = object
-
-proc `=copy`(a: var NoCopies, b: NoCopies) {.error.}
-
-# bug #24720
-proc foo() =
-  var t: Table[int, NoCopies]
-  t[3] = NoCopies() # only moves
-  for k, v in t.pairs(): # lent values, no need to copy!
-    echo "found entry"
-
-foo()

tests/ccgbugs2/m25800.h

@@ -0,0 +1,7 @@
+/*TYPESECTION*/
+struct CppRef {
+  int* data;
+  CppRef() : data(new int(42)) {}
+  ~CppRef() { delete data; data = nullptr; }
+  void reset() { delete data; data = nullptr; }
+};

tests/ccgbugs2/t25800.nim

@@ -0,0 +1,23 @@
+discard """
+  cmd: "nim cpp $file"
+  action: "compile"
+"""
+
+# Bug Report 1: {.importcpp.} on =wasMoved generates invalid preprocessor directive #.
+
+
+type CppRef* {.importcpp, bycopy, noInit, header: "m25800.h".} = object
+
+proc `=destroy`(x: var CppRef) {.importcpp: "#.~CppRef()".}
+proc `=wasMoved`(x: var CppRef) {.importcpp: "#.reset()".}
+proc `=copy`(dest: var CppRef; src: CppRef) {.importcpp: "dest = src".}
+proc `=sink`(dest: var CppRef; src: CppRef) {.importcpp: "dest = std::move(src)".}
+
+# This triggers =wasMoved when passing to sink parameter
+proc consume(x: sink CppRef) = discard
+
+proc test() =
+  var x: CppRef
+  consume(move(x))  # =wasMoved MUST be called here after the move
+
+test()

tests/ccgbugs2/tcodegen.nim

@@ -75,3 +75,19 @@ block: # importc type inheritance
   doAssert(cast[cint](b) == 123)
   var c = foo(b)
   doAssert(cast[cint](c) == 123)
+
+
+# bug #23765
+type
+  X11[T, E] = object
+    m: T
+  B = X11[culonglong, cstring]
+  S = ref object of RootObj
+
+proc j[T, E](m: X11[T, E]): T = discard
+proc n(T: typedesc[SomeUnsignedInt]): X11[T, cstring] = discard
+method call(client: S): uint64 {.base.} =
+  discard j(n(uint64))
+
+var s = S()
+discard s.call()

tests/compiler/tcmdline_import_std_prefix.nim

@@ -0,0 +1,10 @@
+discard """
+  matrix: "-d:nimPreviewSlimSystem --warning:StdPrefix:on --warningAsError:StdPrefix:on --import:std/objectdollar"
+  output: "(a: 23, b: 45)"
+"""
+
+type Foo = object
+  a, b: int
+
+let x = Foo(a: 23, b: 45)
+echo x

tests/concepts/tconcepts_issues.nim

@@ -176,6 +176,42 @@ block t6462:
   var s = SeqGen[int](fil: FilterMixin[int](test: nil, trans: nil))
   doAssert s.test() == nil
 
+block concept_with_cint:
+  # Generic proc matching through concepts with cint should still work
+  type
+    FilterMixin[T] = ref object
+      test: (T) -> bool
+      trans: (T) -> T
+
+    SeqGen[T] = ref object
+      fil: FilterMixin[T]
+
+    WithFilter[T] = concept a
+      a.fil is FilterMixin[T]
+
+  proc test[T](a: WithFilter[T]): (T) -> bool =
+    a.fil.test
+
+  var s = SeqGen[cint](fil: FilterMixin[cint](test: nil, trans: nil))
+  doAssert s.test() == nil
+
+block concept_with_int:
+  type
+    FilterMixin[T] = ref object
+      test: (T) -> bool
+      trans: (T) -> T
+
+    SeqGen[T] = ref object
+      fil: FilterMixin[T]
+
+    WithFilter[T] = concept a
+      a.fil is FilterMixin[T]
+
+  proc test[T](a: WithFilter[T]): (T) -> bool =
+    a.fil.test
+
+  var s = SeqGen[int](fil: FilterMixin[int](test: nil, trans: nil))
+  doAssert s.test() == nil
 
 
 block t6770:

tests/destructor/twasmoved.nim

@@ -12,3 +12,51 @@ proc foo =
   doAssert m.id == 999
 
 foo()
+
+block:
+  type Foo = object
+    a,b,c: int
+
+  var dest: Foo
+
+  # proc `=wasMoved`(x: var Foo) =
+  #   debugEcho "wasMoved called"
+
+  proc main() =
+    var x = Foo(a:11, b:12, c:13)
+    dest = move(x)
+
+  main()
+
+block:
+  type Foo = object
+    a,b,c: int
+
+  var dest: Foo
+
+  proc `=wasMoved`(x: var Foo) =
+    discard "wasMoved called"
+
+  proc main() =
+    var x = Foo(a:11, b:12, c:13)
+    dest = move(x)
+
+  main()
+
+
+import std/threadpool
+
+block:
+  type Foo = object
+    data: string
+
+  proc `=wasMoved`(x: var Foo) =
+    discard
+
+  proc work(x: Foo) =
+    discard
+
+  var x = Foo(data: "hello")
+  spawn work(x)
+  sync()
+

tests/errmsgs/tsso_string_index_var.nim

@@ -0,0 +1,13 @@
+discard """
+  cmd: "nim check --strings:sso --mm:orc --hints:off $file"
+  action: "reject"
+  nimout: '''
+tsso_string_index_var.nim(13, 12) Error: expression 's[0]' is immutable, not 'var'
+'''
+"""
+
+proc passByVar(c: var char) =
+  c = 'x'
+
+var s = "abc"
+passByVar(s[0])

tests/exception/tcpp_handler_raise_finally.nim

@@ -0,0 +1,61 @@
+discard """
+  targets: "cpp"
+  matrix: "--mm:arc; --mm:orc; --mm:refc"
+  output: '''
+inner: orig
+finally
+outer: re:orig
+inner-typeless: orig
+finally-typeless
+outer-typeless: re-tl:orig
+no-catch-finally
+caught-propagated: prop
+'''
+"""
+
+# When an `except` handler raises a new exception, the enclosing `finally`
+# block must still run before the new exception propagates to the outer
+# try.
+#
+# The C++ backend previously emitted the finally's `catch (...)` as a
+# sibling of the user-written catches.  C++ does not allow sibling catches
+# to catch each other's throws, so a handler-raised exception bypassed the
+# finally entirely.  The fix wraps the inner try/catch sequence in an
+# outer try, so any escaping exception (whether from the body or from a
+# handler) is captured before the finally runs.
+
+block typed_except:
+  try:
+    try:
+      raise newException(CatchableError, "orig")
+    except CatchableError as e:
+      echo "inner: ", e.msg
+      raise newException(CatchableError, "re:" & e.msg)
+    finally:
+      echo "finally"
+  except CatchableError as outer:
+    echo "outer: ", outer.msg
+
+block typeless_except:
+  try:
+    try:
+      raise newException(CatchableError, "orig")
+    except:
+      let e = getCurrentException()
+      echo "inner-typeless: ", e.msg
+      raise newException(CatchableError, "re-tl:" & e.msg)
+    finally:
+      echo "finally-typeless"
+  except CatchableError as outer:
+    echo "outer-typeless: ", outer.msg
+
+# try/finally without an except: the body's exception must still propagate
+# after the finally runs.
+block no_catch_finally:
+  try:
+    try:
+      raise newException(CatchableError, "prop")
+    finally:
+      echo "no-catch-finally"
+  except CatchableError as e:
+    echo "caught-propagated: ", e.msg

tests/exception/tcpp_imported_exc.nim

@@ -1,5 +1,5 @@
 discard """
-matrix: "--mm:refc"
+matrix: "--mm:refc; --mm:orc"
 targets: "cpp"
 output: '''
 caught as std::exception

tests/lent/tlent_tuple_address.nim

@@ -0,0 +1,12 @@
+discard """
+  errormsg: "expression has no address"
+"""
+
+iterator foo(x: int): (lent int, lent int) =
+  yield (x, x + 1)
+
+
+var x = 12
+for i in foo(x):
+  echo i[0]
+  echo i[1]

tests/metatype/ttypetraits.nim

@@ -434,3 +434,32 @@ block: # bug #24378
   type Win222[T] = typeof("foobar")
   doAssert not supportsCopyMem((int, Win222[int]))
   doAssert not supportsCopyMem(tuple[a: int, b: Win222[int]])
+
+block: # bug #25789
+  type
+    L[T; N: static int] = distinct seq[T]
+    EPF = distinct L[int, 100]
+
+  var e: EPF = EPF(L[int, 100](@[1, 2, 3]))
+
+  template classifyGeneric[T](x: T): bool =
+    when typeof(x) is L:
+      true
+    else:
+      false
+
+  template classifyConcrete[T](x: T): bool =
+    when typeof(x) is L[int, 100]:
+      true
+    else:
+      false
+
+  let viaConv = L[int, 100](e)
+  doAssert $type(viaConv) == "L[system.int, 100]"
+  doAssert classifyGeneric(viaConv)
+  doAssert classifyConcrete(viaConv)
+
+  let viaDB = distinctBase(e, recursive = false)
+  doAssert $type(viaDB) == "L[system.int, 100]"
+  doAssert classifyGeneric(viaDB)
+  doAssert classifyConcrete(viaDB)

tests/objects/tobject_default_value.nim

@@ -833,4 +833,37 @@ proc overloaded[T: object](x: T) =
     var v: typeof(val)
     overloaded(v)
 
-overloaded(Thing())
+overloaded(Thing())
+
+block:
+  type
+    Foo = object
+      x = Bar()
+
+    Bar = object
+      x: int
+
+  var f = Foo()
+  doassert f.x.x == 0
+
+block:
+  type
+    Foo = object
+      x = Bar(x: 55)
+
+    Bar = object
+      x: int
+
+  var f = Foo()
+  doassert f.x.x == 55
+
+block:
+  type
+    Bar = object
+      x: int
+
+    Foo = object
+      x = Bar()
+
+  var f = Foo()
+  doassert f.x.x == 0

tests/proc/tbackendtypealias.nim

@@ -0,0 +1,44 @@
+# bug #25617
+# Ensure that proc types with backend type alias mismatches
+# (e.g. uint vs csize_t) are rejected at the Nim level rather
+# than producing invalid C code.
+
+discard """
+  cmd: "nim check --hints:off --warnings:off --errorMax:0 $file"
+  action: "reject"
+  nimout: '''
+tbackendtypealias.nim(21, 7) Error: type mismatch: got <proc (len: csize_t){.closure.}> but expected 'proc (len: uint){.closure.}'
+tbackendtypealias.nim(28, 7) Error: type mismatch: got <proc (len: uint){.closure.}> but expected 'proc (len: csize_t){.closure.}'
+'''
+"""
+
+block direct_assignment:
+  # Direct proc variable assignment with backend type alias mismatch
+  var
+    a: proc (len: uint)
+    b: proc (len: csize_t)
+    c = a
+  c = b
+
+block direct_assignment_reverse:
+  var
+    a: proc (len: csize_t)
+    b: proc (len: uint)
+    c = a
+  c = b
+
+block same_backend_type:
+  # Same backend type should still work
+  var
+    a: proc (len: uint)
+    b: proc (len: uint)
+    c = a
+  c = b
+
+block cint_same_type:
+  # cint to cint should work
+  var
+    a: proc (len: cint)
+    b: proc (len: cint)
+    c = a
+  c = b

tests/stdlib/tdeques.nim

@@ -241,3 +241,12 @@ proc main() =
 
 static: main()
 main()
+
+# https://github.com/nim-lang/Nim/issues/18583
+# $ separator must be emitted even when the item's string repr is empty
+type EmptyStr18583 = object
+proc `$`(x: EmptyStr18583): string = ""
+
+block:
+  var d = [EmptyStr18583(), EmptyStr18583()].toDeque
+  doAssert $d == "[, ]", "got: " & $d

tests/stdlib/theapqueue.nim

@@ -104,3 +104,15 @@ template main() =
 
 static: main()
 main()
+
+# https://github.com/nim-lang/Nim/issues/18583
+type EmptyStr18583HeapQ = object
+proc `$`(x: EmptyStr18583HeapQ): string = ""
+proc `<`(a, b: EmptyStr18583HeapQ): bool = false
+
+block:
+  var h = initHeapQueue[EmptyStr18583HeapQ]()
+  push(h, EmptyStr18583HeapQ())
+  push(h, EmptyStr18583HeapQ())
+  let s = $h
+  doAssert s == "[, ]", "got: " & s

tests/stdlib/tlists.nim

@@ -287,3 +287,14 @@ template main =
 
 static: main()
 main()
+
+# https://github.com/nim-lang/Nim/issues/18583
+type EmptyStr18583List = object
+proc `$`(x: EmptyStr18583List): string = ""
+
+block:
+  var L: SinglyLinkedList[EmptyStr18583List]
+  L.prepend(EmptyStr18583List())
+  L.prepend(EmptyStr18583List())
+  let s = $L
+  doAssert s == "[, ]", "got: " & s

tests/stdlib/tpegs.nim

@@ -259,6 +259,11 @@ block:
     doAssert match("EINE ÜBERSICHT UND AUSSERDEM", peg"(\upper \white*)+")
     doAssert(not match("456678", peg"(\letter)+"))
 
+    block:
+      doAssert match("CAFÉ", peg"\i café")
+      doAssert match("Café", peg"\i café")
+      doAssert "two cafés: Café and CAFÉ".findAll(peg"\i café").len == 3
+
     doAssert("var1 = key; var2 = key2".replacef(
       peg"\skip(\s*) {\ident}'='{\ident}", "$1<-$2$2") ==
            "var1<-keykey;var2<-key2key2")

tests/stdlib/tstrformat.nim

@@ -544,6 +544,12 @@ proc main() =
     var x = 5
     doAssert fmt"{(x=7;123.456)=:13e}" == "(x=7;123.456)= 1.234560e+02"
     doAssert x==7
+
+  block: # binary operators in interpolated expressions
+    let n = 1
+    doAssert &"{n-1}" == "0"
+    doAssert fmt"{n-1}" == "0"
+
   block: #curly bracket expressions and tuples
     proc formatValue(result: var string; value:Table|bool|JsonNode; specifier:string) = result.add $value