fixes #6946

compiler/sem.nim

@@ -215,12 +215,17 @@ proc semIdentVis(c: PContext, kind: TSymKind, n: PNode,
 proc semIdentWithPragma(c: PContext, kind: TSymKind, n: PNode,
                         allowed: TSymFlags): PSym
 
-proc typeAllowedCheck(info: TLineInfo; typ: PType; kind: TSymKind) =
-  let t = typeAllowed(typ, kind)
+proc typeAllowedCheck(info: TLineInfo; typ: PType; kind: TSymKind;
+                      flags: TTypeAllowedFlags = {}) =
+  let t = typeAllowed(typ, kind, flags)
   if t != nil:
-    if t == typ: localError(info, "invalid type: '" & typeToString(typ) & "'")
-    else: localError(info, "invalid type: '" & typeToString(t) &
-                           "' in this context: '" & typeToString(typ) & "'")
+    if t == typ:
+      localError(info, "invalid type: '" & typeToString(typ) &
+        "' for " & substr($kind, 2).toLowerAscii)
+    else:
+      localError(info, "invalid type: '" & typeToString(t) &
+        "' in this context: '" & typeToString(typ) &
+        "' for " & substr($kind, 2).toLowerAscii)
 
 proc paramsTypeCheck(c: PContext, typ: PType) {.inline.} =
   typeAllowedCheck(typ.n.info, typ, skProc)

compiler/semstmts.nim

@@ -534,7 +534,7 @@ proc semVarOrLet(c: PContext, n: PNode, symkind: TSymKind): PNode =
 
     # this can only happen for errornous var statements:
     if typ == nil: continue
-    typeAllowedCheck(a.info, typ, symkind)
+    typeAllowedCheck(a.info, typ, symkind, if c.matchedConcept != nil: {taConcept} else: {})
     liftTypeBoundOps(c, typ, a.info)
     var tup = skipTypes(typ, {tyGenericInst, tyAlias, tySink})
     if a.kind == nkVarTuple:

compiler/types.nim

@@ -1058,11 +1058,12 @@ proc commonSuperclass*(a, b: PType): PType =
     y = y.sons[0]
 
 type
-  TTypeAllowedFlag = enum
+  TTypeAllowedFlag* = enum
     taField,
-    taHeap
+    taHeap,
+    taConcept
 
-  TTypeAllowedFlags = set[TTypeAllowedFlag]
+  TTypeAllowedFlags* = set[TTypeAllowedFlag]
 
 proc typeAllowedAux(marker: var IntSet, typ: PType, kind: TSymKind,
                     flags: TTypeAllowedFlags = {}): PType
@@ -1130,7 +1131,10 @@ proc typeAllowedAux(marker: var IntSet, typ: PType, kind: TSymKind,
   of tyVoid:
     if taField notin flags: result = t
   of tyTypeClasses:
-    if not (tfGenericTypeParam in t.flags or taField notin flags): result = t
+    if tfGenericTypeParam in t.flags or taConcept in flags: #or taField notin flags:
+      discard
+    elif kind notin {skParam, skResult}:
+      result = t
   of tyGenericBody, tyGenericParam, tyGenericInvocation,
      tyNone, tyForward, tyFromExpr:
     result = t
@@ -1178,11 +1182,11 @@ proc typeAllowedAux(marker: var IntSet, typ: PType, kind: TSymKind,
     result = nil
   of tyUnused, tyOptAsRef: internalError("typeAllowedAux")
 
-proc typeAllowed*(t: PType, kind: TSymKind): PType =
+proc typeAllowed*(t: PType, kind: TSymKind; flags: TTypeAllowedFlags = {}): PType =
   # returns 'nil' on success and otherwise the part of the type that is
   # wrong!
   var marker = initIntSet()
-  result = typeAllowedAux(marker, t, kind, {})
+  result = typeAllowedAux(marker, t, kind, flags)
 
 proc align(address, alignment: BiggestInt): BiggestInt =
   result = (address + (alignment - 1)) and not (alignment - 1)