fix nim-lang#13182: proc fun(a: varargs[Foo, conv]) now can be over…

…loaded

compiler/semcall.nim

@@ -565,7 +565,7 @@ proc semOverloadedCall(c: PContext, n, nOrig: PNode,
       # this time enabling all the diagnostic output (this should fail again)
       discard semOverloadedCall(c, n, nOrig, filter, flags + {efExplain})
     elif efNoUndeclared notin flags:
-      notFoundError(c, n, errors)
+      if c.depthSigmatchVarargs == 0: notFoundError(c, n, errors)
 
 proc explicitGenericInstError(c: PContext; n: PNode): PNode =
   localError(c.config, getCallLineInfo(n), errCannotInstantiateX % renderTree(n))

compiler/semdata.nim

@@ -139,6 +139,11 @@ type
       # would otherwise fail.
     unusedImports*: seq[(PSym, TLineInfo)]
     exportIndirections*: HashSet[(int, int)]
+    depthSigmatchVarargs*: int
+      # for protection against issue #13182:
+      # when we sigmatch against `fun(a: varargs[Foo, conv])`, this
+      # calls a nested sigmatch for `conv`, but that nested sigmatch shouldn't
+      # generate an error by itself before whole overload resolution takes place
 
 template config*(c: PContext): ConfigRef = c.graph.config
 

compiler/sigmatch.nim

@@ -2456,8 +2456,12 @@ proc matchesAux(c: PContext, n, nOrig: PNode,
           m.baseTypeMatch = false
           m.typedescMatched = false
           n[a] = prepareOperand(c, formal.typ, n[a])
+          let old = m.c.depthSigmatchVarargs
+          m.c.depthSigmatchVarargs.inc
           arg = paramTypesMatch(m, formal.typ, n[a].typ,
                                     n[a], nOrig[a])
+          m.c.depthSigmatchVarargs.dec
+          assert m.c.depthSigmatchVarargs == old
           if arg == nil:
             noMatch()
             return