Sema: Add separate pass for checkConformancesInContext()

I tried doing this directly from typeCheckDecl(), but it breaks
associated type inference. We can figure this out later when
declaration checking becomes lazier and more incremental.

Note that typo correction does not force witnesses of
synthesized conformances. This means that a typo correction
from a top-level form will no longer pick up synthesized
witnesses, and will find the protocol requirement instead.

To give a test the same behavior as before, I put the
expression in a function body instead of a top-level form.

Note that we already had the same behavior with typo
correction from pattern binding initializers and other
contexts that are type checked before conformances.

Author: slavapestov

lib/Sema/TypeCheckDecl.cpp

@@ -4354,7 +4354,6 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
       for (Decl *member : ED->getMembers())
         visit(member);
 
-      TC.checkConformancesInContext(ED, ED);
       return;
     }
 
@@ -4387,14 +4386,14 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
     }
 
     TC.checkDeclCircularity(ED);
+    TC.ConformanceContexts.push_back(ED);
   }
 
   void visitStructDecl(StructDecl *SD) {
     if (!IsFirstPass) {
       for (Decl *Member : SD->getMembers())
         visit(Member);
 
-      TC.checkConformancesInContext(SD, SD);
       return;
     }
 
@@ -4415,6 +4414,7 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
     checkAccessControl(TC, SD);
 
     TC.checkDeclCircularity(SD);
+    TC.ConformanceContexts.push_back(SD);
   }
 
   /// Check whether the given properties can be @NSManaged in this class.
@@ -4525,7 +4525,6 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
       for (Decl *Member : CD->getMembers())
         visit(Member);
 
-      TC.checkConformancesInContext(CD, CD);
       return;
     }
 
@@ -4649,6 +4648,7 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
     checkAccessControl(TC, CD);
 
     TC.checkDeclCircularity(CD);
+    TC.ConformanceContexts.push_back(CD);
   }
 
   void visitProtocolDecl(ProtocolDecl *PD) {
@@ -6241,7 +6241,7 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
     for (Decl *Member : ED->getMembers())
       visit(Member);
 
-    TC.checkConformancesInContext(ED, ED);
+    TC.ConformanceContexts.push_back(ED);
 
     if (!ED->isInvalid())
       TC.checkDeclAttributes(ED);

lib/Sema/TypeChecker.cpp

@@ -442,6 +442,18 @@ static void typeCheckFunctionsAndExternalDecls(SourceFile &SF, TypeChecker &TC)
   unsigned currentExternalDef = TC.Context.LastCheckedExternalDefinition;
   unsigned currentSynthesizedDecl = SF.LastCheckedSynthesizedDecl;
   do {
+    // Type check conformance contexts.
+    for (unsigned i = 0; i != TC.ConformanceContexts.size(); ++i) {
+      auto decl = TC.ConformanceContexts[i];
+      if (auto *ext = dyn_cast<ExtensionDecl>(decl))
+        TC.checkConformancesInContext(ext, ext);
+      else {
+        auto *ntd = cast<NominalTypeDecl>(decl);
+        TC.checkConformancesInContext(ntd, ntd);
+      }
+    }
+    TC.ConformanceContexts.clear();
+
     // Type check the body of each of the function in turn.  Note that outside
     // functions must be visited before nested functions for type-checking to
     // work correctly.
@@ -523,6 +535,7 @@ static void typeCheckFunctionsAndExternalDecls(SourceFile &SF, TypeChecker &TC)
            currentExternalDef < TC.Context.ExternalDefinitions.size() ||
            currentSynthesizedDecl < SF.SynthesizedDecls.size() ||
            !TC.DeclsToFinalize.empty() ||
+           !TC.ConformanceContexts.empty() ||
            !TC.DelayedRequirementSignatures.empty() ||
            !TC.UsedConformances.empty() ||
            !TC.PartiallyCheckedConformances.empty());

lib/Sema/TypeChecker.h

@@ -711,6 +711,9 @@ class TypeChecker final : public LazyResolver {
   /// \brief The list of function definitions we've encountered.
   std::vector<AbstractFunctionDecl *> definedFunctions;
 
+  /// Declarations that need their conformances checked.
+  llvm::SmallVector<Decl *, 8> ConformanceContexts;
+
   /// The list of protocol conformances that were "used" and will need to be
   /// completed before type checking is considered complete.
   llvm::SetVector<NormalProtocolConformance *> UsedConformances;

test/decl/enum/enumtest.swift

@@ -313,7 +313,10 @@ print(E21269142.Foo.rawValue)  // expected-error {{value of type 'E21269142' has
 enum SyntheticMember { // expected-note {{did you mean the implicitly-synthesized property 'hashValue'?}}
   case Foo
 }
-print(SyntheticMember.Foo.hasValue) // expected-error {{value of type 'SyntheticMember' has no member 'hasValue'}}
+
+func useSynthesizedMember() {
+  print(SyntheticMember.Foo.hasValue) // expected-error {{value of type 'SyntheticMember' has no member 'hasValue'}}
+}
 
 // Non-materializable argument type
 enum Lens<T> {