gensym anonymous proc symbols (#24422)

fixes #14067, fixes #15004, fixes #19019

Anonymous procs are [added to
scope](https://github.com/nim-lang/Nim/blob/8091d76306c23b866af00d384b9b6f929ef8ed23/compiler/semstmts.nim#L2466)
with the name `:anonymous`. This means that if they have the same
signature in a scope, they can consider each other as redefinitions. To
prevent this, mark their symbols as `sfGenSym` so they do not get added
to scope or cause any name conflicts. The commented out `and not isAnon`
check wouldn't work because `isAnon` would not be true if the proc is
being resemmed, in which case the name field in the proc AST would have
the symbol of the anonymous proc rather than being empty.

There is a separate problem of default values in generic/normal procs
not opening new scopes which is partially responsible for #19019.

compiler/semstmts.nim

@@ -2359,6 +2359,7 @@ proc semProcAux(c: PContext, n: PNode, kind: TSymKind,
   of nkEmpty:
     s = newSym(kind, c.cache.idAnon, c.idgen, c.getCurrOwner, n.info)
     s.flags.incl sfUsed
+    s.flags.incl sfGenSym
     n[namePos] = newSymNode(s)
   of nkSym:
     s = n[namePos].sym

tests/proc/tanonprocresem.nim

@@ -0,0 +1,41 @@
+block: # issue #19019
+  proc start(draw:proc=(proc()=echo "default"), init:proc=(proc()=echo "default"), reshape:proc=(proc()=echo "default"))=discard
+  start()
+
+block: # issue #14067
+  type
+    Result[T, E] = object
+
+    DataProc = proc(val: openArray[byte])
+    GetProc = proc (onData: DataProc): Result[bool, cstring]
+
+  func get[T, E](self: Result[T, E]): T =
+    discard
+
+  template `[]`[T, E](self: Result[T, E]): T =
+    self.get()
+
+  proc testKVStore() =
+    var v: seq[byte]
+    var p: GetProc
+
+    discard p(proc(data: openArray[byte]) =
+        v = @data
+      )[]
+
+  if false: testKVStore()
+
+import std/macros
+
+block: # issue #15004
+  macro fn(fun:untyped):untyped =
+    newTree(nnkTupleConstr, newLit"first", fun)
+
+  macro fn(key:string, fun:untyped):untyped =
+    newTree(nnkTupleConstr, newLit"second", fun)
+
+  let c = fn(proc(count:int):string =
+    return "x = " & $count
+  )
+  doAssert c[0] == "first"
+  doAssert c[1](123) == "x = 123"