[Module-scope lookup] Don't expand macros associated with members of types

The module-scope lookup tables use the same code for adding
module-scope declarations as for adding member operators, which are
found via "global" operator lookup. This requires us to expand macros
that can produce members of types, which violates the outside-in
expansion rule described in the proposals.

Stop recording member-producing macros, whether they are peer macros
applied to member declarations or are freestanding declaration macros
within a member context. This re-establishes the outside-in expansion
rule. It also means that member operators introduced by macro
expansion won't be found by global operator lookup, which is a
(necessary) semantic change.

Author: DougGregor

lib/AST/Module.cpp

@@ -249,7 +249,7 @@ void SourceLookupCache::addToUnqualifiedLookupCache(Range decls,
         // Cache the value under both its compound name and its full name.
         TopLevelValues.add(VD);
 
-        if (VD->getAttrs().hasAttribute<CustomAttr>()) {
+        if (!onlyOperators && VD->getAttrs().hasAttribute<CustomAttr>()) {
           MayHaveAuxiliaryDecls.push_back(VD);
         }
       }
@@ -279,8 +279,10 @@ void SourceLookupCache::addToUnqualifiedLookupCache(Range decls,
     else if (auto *PG = dyn_cast<PrecedenceGroupDecl>(D))
       PrecedenceGroups[PG->getName()].push_back(PG);
 
-    else if (auto *MED = dyn_cast<MacroExpansionDecl>(D))
-      MayHaveAuxiliaryDecls.push_back(MED);
+    else if (auto *MED = dyn_cast<MacroExpansionDecl>(D)) {
+      if (!onlyOperators)
+        MayHaveAuxiliaryDecls.push_back(MED);
+    }
   }
 }
 
@@ -403,13 +405,6 @@ void SourceLookupCache::populateAuxiliaryDeclCache() {
     for (auto macroNames : introducedNames) {
       auto macroRef = macroNames.getFirst();
       for (auto name : macroNames.getSecond()) {
-
-        // If this macro isn't in a module-scope context, and the introduced
-        // name isn't an operator, we shouldn't be able to see it.
-        if (!decl->getDeclContext()->isModuleScopeContext() &&
-            !name.getBaseName().isOperator())
-          continue;
-
         auto *placeholder = MissingDecl::forUnexpandedMacro(macroRef, decl);
         name.addToLookupTable(TopLevelAuxiliaryDecls, placeholder);
       }
@@ -492,12 +487,6 @@ void SourceLookupCache::lookupValue(DeclName Name, NLKind LookupKind,
   for (auto *unexpandedDecl : unexpandedDecls) {
     unexpandedDecl->forEachMacroExpandedDecl(
         [&](ValueDecl *decl) {
-          // If the declaration is not a module-scope declaration, and
-          // isn't an operator, ignore it.
-          if (!decl->getDeclContext()->isModuleScopeContext() &&
-              !decl->getName().getBaseName().isOperator())
-            return;
-
           if (decl->getName().matchesRef(Name)) {
             if (macroExpandedDecls.insert(decl).second)
               Result.push_back(decl);

test/Macros/macro_expand.swift

@@ -468,15 +468,11 @@ struct HasEqualsSelf4 {
 func testHasEqualsSelf(
   x: HasEqualsSelf, y: HasEqualsSelf2, z: HasEqualsSelf3, w: HasEqualsSelf4
 ) {
-  _ = (x == true)
-  _ = (y == true)
 #if TEST_DIAGNOSTICS
-  // FIXME: This is technically a bug, because we should be able to find the
-  // == operator introduced through a member operator. However, we might
-  // want to change the rule rather than implement this.
-  _ = (z == true) // expected-error{{binary operator '==' cannot be applied to operands}}
-  // expected-note@-1{{overloads for '==' exist with these partially matching parameter lists}}
-  _ = (w == true) // expected-error{{binary operator '==' cannot be applied to operands}}
-  // expected-note@-1{{overloads for '==' exist with these partially matching parameter lists}}
+  // Global operator lookup doesn't find member operators introduced by macros.
+  _ = (x == true) // expected-error{{cannot convert value of type}}
+  _ = (y == true) // expected-error{{cannot convert value of type}}
+  _ = (z == true) // expected-error{{cannot convert value of type}}
+  _ = (w == true) // expected-error{{cannot convert value of type}}
   #endif
 }