resolve unambiguous enum symchoices from local scope, error on rest (#22606)

fixes #22598, properly fixes #21887 and fixes test case issue number

When an enum field sym choice has to choose a type, check if its name is
ambiguous in the local scope, then check if the first symbol found in
the local scope is the first symbol in the sym choice. If so, choose
that symbol. Otherwise, give an ambiguous identifier error.

The dependence on the local scope implies this will always give
ambiguity errors for unpicked enum symchoices from generics and
templates and macros from other scopes. We can change `not
isAmbiguous(...) and foundSym == first` to `not (isAmbiguous(...) and
foundSym == first)` to make it so they never give ambiguity errors, and
always pick the first symbol in the symchoice. I can do this if this is
preferred, but no code from CI seems affected.

compiler/lookups.nim

@@ -254,6 +254,41 @@ proc searchInScopesFilterBy*(c: PContext, s: PIdent, filter: TSymKinds): seq[PSy
         if s.kind in filter:
           result.add s
 
+proc isAmbiguous*(c: PContext, s: PIdent, filter: TSymKinds, sym: var PSym): bool =
+  result = false
+  block outer:
+    for scope in allScopes(c.currentScope):
+      var ti: TIdentIter
+      var candidate = initIdentIter(ti, scope.symbols, s)
+      var scopeHasCandidate = false
+      while candidate != nil:
+        if candidate.kind in filter:
+          if scopeHasCandidate:
+            # 2 candidates in same scope, ambiguous
+            return true
+          else:
+            scopeHasCandidate = true
+            sym = candidate
+        candidate = nextIdentIter(ti, scope.symbols)
+      if scopeHasCandidate:
+        # scope had a candidate but wasn't ambiguous
+        return false
+
+  var importsHaveCandidate = false
+  var marked = initIntSet()
+  for im in c.imports.mitems:
+    for s in symbols(im, marked, s, c.graph):
+      if s.kind in filter:
+        if importsHaveCandidate:
+          # 2 candidates among imports, ambiguous
+          return true
+        else:
+          importsHaveCandidate = true
+          sym = s
+  if importsHaveCandidate:
+    # imports had a candidate but wasn't ambiguous
+    return false
+
 proc errorSym*(c: PContext, n: PNode): PSym =
   ## creates an error symbol to avoid cascading errors (for IDE support)
   var m = n

compiler/semexprs.nim

@@ -92,7 +92,10 @@ proc semExprCheck(c: PContext, n: PNode, flags: TExprFlags, expectedType: PType
 
 proc ambiguousSymChoice(c: PContext, orig, n: PNode): PNode =
   let first = n[0].sym
-  if first.kind == skEnumField:
+  var foundSym: PSym = nil
+  if first.kind == skEnumField and
+      not isAmbiguous(c, first.name, {skEnumField}, foundSym) and
+      foundSym == first:
     # choose the first resolved enum field, i.e. the latest in scope
     # to mirror behavior before overloadable enums
     if hintAmbiguousEnum in c.config.notes:

tests/enum/tambiguousoverloads.nim

@@ -0,0 +1,26 @@
+discard """
+cmd: "nim check --hints:off $file"
+"""
+
+block: # bug #21887
+  type
+    EnumA = enum A = 300, B
+    EnumB = enum A = 10
+    EnumC = enum C
+
+  doAssert typeof(EnumC(A)) is EnumC #[tt.Error
+                       ^ ambiguous identifier 'A' -- use one of the following:
+  EnumA.A: EnumA
+  EnumB.A: EnumB]#
+
+block: # issue #22598
+  type
+    A = enum
+      red
+    B = enum
+      red
+
+  let a = red #[tt.Error
+          ^ ambiguous identifier 'red' -- use one of the following:
+  A.red: A
+  B.red: B]#

tests/enum/toverloadable_enums.nim

@@ -118,11 +118,3 @@ block: # test with macros/templates
   doAssert isOneMS(e2)
   doAssert isOneT(e1)
   doAssert isOneT(e2)
-
-block: # bug #21908
-  type
-    EnumA = enum A = 300, B
-    EnumB = enum A = 10
-    EnumC = enum C
-
-  doAssert typeof(EnumC(A)) is EnumC

tests/lookups/tambsym3.nim

@@ -1,15 +1,12 @@
 discard """
-  errormsg: "ambiguous enum field"
+  errormsg: "ambiguous identifier 'mDec' -- use one of the following:"
   file: "tambsym3.nim"
-  line: 14
+  line: 11
 """
 # Test ambiguous symbols
 
 import mambsym1, times
 
-{.hint[AmbiguousEnum]: on.}
-{.hintAsError[AmbiguousEnum]: on.}
-
 var
   v = mDec #ERROR_MSG ambiguous identifier