destructors now work with overloaded assignment operators; fixes #2811; fixes #1632

compiler/semdestruct.nim

@@ -177,6 +177,15 @@ proc instantiateDestructor(c: PContext, typ: PType): PType =
   else:
     return nil
 
+proc createDestructorCall(c: PContext, s: PSym): PNode =
+  let varTyp = s.typ
+  if varTyp == nil or sfGlobal in s.flags: return
+  let destructableT = instantiateDestructor(c, varTyp)
+  if destructableT != nil:
+    let call = semStmt(c, newNode(nkCall, s.info, @[
+      useSym(destructableT.destructor), useSym(s)]))
+    result = newNode(nkDefer, s.info, @[call])
+
 proc insertDestructors(c: PContext,
                        varSection: PNode): tuple[outer, inner: PNode] =
   # Accepts a var or let section.

compiler/semexprs.nim

@@ -2259,7 +2259,10 @@ proc semExpr(c: PContext, n: PNode, flags: TExprFlags = {}): PNode =
   of nkStaticStmt:
     result = semStaticStmt(c, n)
   of nkDefer:
-    localError(n.info, errGenerated, "'defer' not allowed in this context")
+    n.sons[0] = semExpr(c, n.sons[0])
+    if not n.sons[0].typ.isEmptyType:
+      localError(n.info, errGenerated, "'defer' takes a 'void' expression")
+    #localError(n.info, errGenerated, "'defer' not allowed in this context")
   else:
     localError(n.info, errInvalidExpressionX,
                renderTree(n, {renderNoComments}))

compiler/semstmts.nim

@@ -369,6 +369,15 @@ proc addToVarSection(c: PContext; result: var PNode; orig, identDefs: PNode) =
   else:
     result.add identDefs
 
+proc addDefer(c: PContext; result: var PNode; s: PSym) =
+  let deferDestructorCall = createDestructorCall(c, s)
+  if deferDestructorCall != nil:
+    if result.kind != nkStmtList:
+      let oldResult = result
+      result = newNodeI(nkStmtList, result.info)
+      result.add oldResult
+    result.add deferDestructorCall
+
 proc isDiscardUnderscore(v: PSym): bool =
   if v.name.s == "_":
     v.flags.incl(sfGenSym)
@@ -469,6 +478,7 @@ proc semVarOrLet(c: PContext, n: PNode, symkind: TSymKind): PNode =
         if def.kind == nkPar: v.ast = def[j]
         v.typ = tup.sons[j]
         b.sons[j] = newSymNode(v)
+      addDefer(c, result, v)
       checkNilable(v)
       if sfCompileTime in v.flags: hasCompileTime = true
   if hasCompileTime: vm.setupCompileTimeVar(c.module, result)
@@ -1371,7 +1381,7 @@ proc semStmtList(c: PContext, n: PNode, flags: TExprFlags): PNode =
   for i in countup(0, length - 1):
     let k = n.sons[i].kind
     case k
-    of nkFinally, nkExceptBranch, nkDefer:
+    of nkFinally, nkExceptBranch:
       # stand-alone finally and except blocks are
       # transformed into regular try blocks:
       #
@@ -1424,14 +1434,6 @@ proc semStmtList(c: PContext, n: PNode, flags: TExprFlags): PNode =
         n.typ = n.sons[i].typ
         if not isEmptyType(n.typ): n.kind = nkStmtListExpr
       case n.sons[i].kind
-      of nkVarSection, nkLetSection:
-        let (outer, inner) = insertDestructors(c, n.sons[i])
-        if outer != nil:
-          n.sons[i] = outer
-          var rest = newNode(nkStmtList, n.info, n.sons[i+1 .. length-1])
-          inner.addSon(semStmtList(c, rest, flags))
-          n.sons.setLen(i+1)
-          return
       of LastBlockStmts:
         for j in countup(i + 1, length - 1):
           case n.sons[j].kind

compiler/transf.nim

@@ -16,6 +16,7 @@
 # * converts "continue" to "break"; disambiguates "break"
 # * introduces method dispatchers
 # * performs lambda lifting for closure support
+# * transforms 'defer' into a 'try finally' statement
 
 import
   intsets, strutils, lists, options, ast, astalgo, trees, treetab, msgs, os,
@@ -44,6 +45,7 @@ type
     inlining: int            # > 0 if we are in inlining context (copy vars)
     nestedProcs: int         # > 0 if we are in a nested proc
     contSyms, breakSyms: seq[PSym]  # to transform 'continue' and 'break'
+    deferDetected: bool
   PTransf = ref TTransfContext
 
 proc newTransNode(a: PNode): PTransNode {.inline.} =
@@ -680,6 +682,14 @@ proc commonOptimizations*(c: PSym, n: PNode): PNode =
       result = n
 
 proc transform(c: PTransf, n: PNode): PTransNode =
+  when false:
+    var oldDeferAnchor: PNode
+    if n.kind in {nkElifBranch, nkOfBranch, nkExceptBranch, nkElifExpr,
+                  nkElseExpr, nkElse, nkForStmt, nkWhileStmt, nkFinally,
+                  nkBlockStmt, nkBlockExpr}:
+      oldDeferAnchor = c.deferAnchor
+      c.deferAnchor = n
+
   case n.kind
   of nkSym:
     result = transformSym(c, n)
@@ -712,13 +722,36 @@ proc transform(c: PTransf, n: PNode): PTransNode =
     result = transformFor(c, n)
   of nkParForStmt:
     result = transformSons(c, n)
-  of nkCaseStmt: result = transformCase(c, n)
+  of nkCaseStmt:
+    result = transformCase(c, n)
+  of nkWhileStmt: result = transformWhile(c, n)
+  of nkBlockStmt, nkBlockExpr:
+    result = transformBlock(c, n)
+  of nkDefer:
+    c.deferDetected = true
+    result = transformSons(c, n)
+    when false:
+      let deferPart = newNodeI(nkFinally, n.info)
+      deferPart.add n.sons[0]
+      let tryStmt = newNodeI(nkTryStmt, n.info)
+      if c.deferAnchor.isNil:
+        tryStmt.add c.root
+        c.root = tryStmt
+        result = PTransNode(tryStmt)
+      else:
+        # modify the corresponding *action*, don't rely on nkStmtList:
+        let L = c.deferAnchor.len-1
+        tryStmt.add c.deferAnchor.sons[L]
+        c.deferAnchor.sons[L] = tryStmt
+        result = newTransNode(nkCommentStmt, n.info, 0)
+      tryStmt.addSon(deferPart)
+      # disable the original 'defer' statement:
+      n.kind = nkCommentStmt
   of nkContinueStmt:
     result = PTransNode(newNodeI(nkBreakStmt, n.info))
     var labl = c.contSyms[c.contSyms.high]
     add(result, PTransNode(newSymNode(labl)))
   of nkBreakStmt: result = transformBreak(c, n)
-  of nkWhileStmt: result = transformWhile(c, n)
   of nkCallKinds:
     result = transformCall(c, n)
   of nkAddr, nkHiddenAddr:
@@ -754,8 +787,6 @@ proc transform(c: PTransf, n: PNode): PTransNode =
       result = transformYield(c, n)
     else:
       result = transformSons(c, n)
-  of nkBlockStmt, nkBlockExpr:
-    result = transformBlock(c, n)
   of nkIdentDefs, nkConstDef:
     result = transformSons(c, n)
     # XXX comment handling really sucks:
@@ -764,6 +795,8 @@ proc transform(c: PTransf, n: PNode): PTransNode =
   of nkClosure: return PTransNode(n)
   else:
     result = transformSons(c, n)
+  when false:
+    if oldDeferAnchor != nil: c.deferAnchor = oldDeferAnchor
   var cnst = getConstExpr(c.module, PNode(result))
   # we inline constants if they are not complex constants:
   if cnst != nil and not dontInlineConstant(n, cnst):
@@ -785,12 +818,52 @@ proc openTransf(module: PSym, filename: string): PTransf =
   result.breakSyms = @[]
   result.module = module
 
+proc flattenStmts(n: PNode) =
+  var goOn = true
+  while goOn:
+    goOn = false
+    for i in 0..<n.len:
+      let it = n[i]
+      if it.kind in {nkStmtList, nkStmtListExpr}:
+        n.sons[i..i] = it.sons[0..<it.len]
+        goOn = true
+
+proc liftDeferAux(n: PNode) =
+  if n.kind in {nkStmtList, nkStmtListExpr}:
+    flattenStmts(n)
+    var goOn = true
+    while goOn:
+      goOn = false
+      let last = n.len-1
+      for i in 0..last:
+        if n.sons[i].kind == nkDefer:
+          let deferPart = newNodeI(nkFinally, n.sons[i].info)
+          deferPart.add n.sons[i].sons[0]
+          var tryStmt = newNodeI(nkTryStmt, n.sons[i].info)
+          var body = newNodeI(nkStmtList, n.sons[i].info)
+          if i < last:
+            body.sons = n.sons[(i+1)..last]
+          tryStmt.addSon(body)
+          tryStmt.addSon(deferPart)
+          n.sons[i] = tryStmt
+          n.sons.setLen(i+1)
+          n.typ = n.sons[i].typ
+          goOn = true
+          break
+  for i in 0..n.safeLen-1:
+    liftDeferAux(n.sons[i])
+
+template liftDefer(c, root) =
+  if c.deferDetected:
+    liftDeferAux(root)
+
 proc transformBody*(module: PSym, n: PNode, prc: PSym): PNode =
   if nfTransf in n.flags or prc.kind in {skTemplate}:
     result = n
   else:
     var c = openTransf(module, "")
     result = processTransf(c, n, prc)
+    liftDefer(c, result)
     result = liftLambdas(prc, result)
     #if prc.kind == skClosureIterator:
     #  result = lambdalifting.liftIterator(prc, result)
@@ -805,6 +878,7 @@ proc transformStmt*(module: PSym, n: PNode): PNode =
   else:
     var c = openTransf(module, "")
     result = processTransf(c, n, module)
+    liftDefer(c, result)
     result = liftLambdasForTopLevel(module, result)
     incl(result.flags, nfTransf)
     when useEffectSystem: trackTopLevelStmt(module, result)
@@ -815,4 +889,5 @@ proc transformExpr*(module: PSym, n: PNode): PNode =
   else:
     var c = openTransf(module, "")
     result = processTransf(c, n, module)
+    liftDefer(c, result)
     incl(result.flags, nfTransf)

tests/destructor/tdestructor3.nim

@@ -0,0 +1,47 @@
+discard """
+  output: '''assign
+destroy
+destroy
+destroy Foo: 5
+5
+destroy Foo: 123
+123'''
+"""
+
+# bug #2821
+{.experimental.}
+
+type T = object
+
+proc `=`(lhs: var T, rhs: T) =
+    echo "assign"
+
+proc `=destroy`(v: var T) =
+    echo "destroy"
+
+block:
+    var v1 : T
+    var v2 : T = v1
+
+
+# bug #1632
+
+type
+  Foo = object of RootObj
+    x: int
+
+proc `=destroy`(a: var Foo) =
+  echo "destroy Foo: " & $a.x
+
+template toFooPtr(a: int{lit}): ptr Foo =
+  var temp = Foo(x:a)
+  temp.addr
+
+proc test(a: ptr Foo) =
+  echo a[].x
+
+proc main =
+  test(toFooPtr(5))
+  test(toFooPtr(123))
+
+main()

tests/exception/tdefer1.nim

@@ -1,6 +1,10 @@
 discard """
   output: '''hi
-hi'''
+hi
+1
+hi
+B
+A'''
 """
 
 # bug #1742
@@ -16,3 +20,23 @@ import strutils
 let x = try: parseInt("133a")
         except: -1
         finally: echo "hi"
+
+
+template atFuncEnd =
+  defer:
+    echo "A"
+  defer:
+    echo "B"
+
+template testB(): expr =
+    let a = 0
+    defer: echo "hi" # Delete this line to make it work
+    a
+
+proc main =
+  atFuncEnd()
+  echo 1
+  let i = testB()
+  echo 2
+
+main()