[CS] Use correct DeclContext when solving initializations

Use the PatternBindingInitializer context if we
have one. This also uncovered a parser issue where
we would mistakenly create a
PatternBindingInitializer in top-level code.

Author: hamishknight

include/swift/Sema/SyntacticElementTarget.h

@@ -254,7 +254,7 @@ class SyntacticElementTarget {
   /// Form a target for the initialization of a pattern binding entry from
   /// an expression.
   static SyntacticElementTarget
-  forInitialization(Expr *initializer, DeclContext *dc, Type patternType,
+  forInitialization(Expr *initializer, Type patternType,
                     PatternBindingDecl *patternBinding,
                     unsigned patternBindingIndex, bool bindPatternVarsOneWay);
 

lib/Parse/ParseDecl.cpp

@@ -8236,7 +8236,7 @@ Parser::parseDeclVar(ParseDeclOptions Flags,
   // In var/let decl with multiple patterns, accumulate them all in this list
   // so we can build our singular PatternBindingDecl at the end.
   SmallVector<PatternBindingEntry, 4> PBDEntries;
-  auto BaseContext = CurDeclContext;
+  DeclContext *BindingContext = topLevelDecl ? topLevelDecl : CurDeclContext;
 
   // No matter what error path we take, make sure the
   // PatternBindingDecl/TopLevel code block are added.
@@ -8251,13 +8251,12 @@ Parser::parseDeclVar(ParseDeclOptions Flags,
     // can finally create our PatternBindingDecl to represent the
     // pattern/initializer pairs.
     auto *PBD = PatternBindingDecl::create(Context, StaticLoc, StaticSpelling,
-                                           VarLoc, PBDEntries, BaseContext);
+                                           VarLoc, PBDEntries, BindingContext);
 
     // If we're setting up a TopLevelCodeDecl, configure it by setting up the
     // body that holds PBD and we're done.  The TopLevelCodeDecl is already set
     // up in Decls to be returned to caller.
     if (topLevelDecl) {
-      PBD->setDeclContext(topLevelDecl);
       auto range = PBD->getSourceRangeIncludingAttrs();
       topLevelDecl->setBody(BraceStmt::create(Context, range.Start,
                                               ASTNode(PBD), range.End, true));

lib/Sema/CSGen.cpp

@@ -4547,7 +4547,7 @@ generateForEachStmtConstraints(ConstraintSystem &cs, DeclContext *dc,
         ctx, StaticSpellingKind::None, pattern, makeIteratorCall, dc);
 
     auto makeIteratorTarget = SyntacticElementTarget::forInitialization(
-        makeIteratorCall, dc, /*patternType=*/Type(), PB, /*index=*/0,
+        makeIteratorCall, /*patternType=*/Type(), PB, /*index=*/0,
         /*shouldBindPatternsOneWay=*/false);
 
     ContextualTypeInfo contextInfo(sequenceProto->getDeclaredInterfaceType(),
@@ -4870,7 +4870,7 @@ bool ConstraintSystem::generateConstraints(
       }
 
       auto target = init ? SyntacticElementTarget::forInitialization(
-                               init, dc, patternType, patternBinding, index,
+                               init, patternType, patternBinding, index,
                                /*bindPatternVarsOneWay=*/true)
                          : SyntacticElementTarget::forUninitializedVar(
                                patternBinding, index, patternType);

lib/Sema/CSSyntacticElement.cpp

@@ -751,8 +751,7 @@ class SyntacticElementConstraintGenerator
     // declaring local wrapped variables (yet).
     if (hasPropertyWrapper(pattern)) {
       auto target = SyntacticElementTarget::forInitialization(
-          init, patternBinding->getDeclContext(), patternType, patternBinding,
-          index,
+          init, patternType, patternBinding, index,
           /*bindPatternVarsOneWay=*/false);
 
       if (ConstraintSystem::preCheckTarget(
@@ -764,8 +763,7 @@ class SyntacticElementConstraintGenerator
 
     if (init) {
       return SyntacticElementTarget::forInitialization(
-          init, patternBinding->getDeclContext(), patternType, patternBinding,
-          index,
+          init, patternType, patternBinding, index,
           /*bindPatternVarsOneWay=*/false);
     }
 

lib/Sema/SyntacticElementTarget.cpp

@@ -165,9 +165,12 @@ SyntacticElementTarget::forInitialization(Expr *initializer, DeclContext *dc,
 }
 
 SyntacticElementTarget SyntacticElementTarget::forInitialization(
-    Expr *initializer, DeclContext *dc, Type patternType,
-    PatternBindingDecl *patternBinding, unsigned patternBindingIndex,
-    bool bindPatternVarsOneWay) {
+    Expr *initializer, Type patternType, PatternBindingDecl *patternBinding,
+    unsigned patternBindingIndex, bool bindPatternVarsOneWay) {
+  auto *dc = patternBinding->getDeclContext();
+  if (auto *initContext = patternBinding->getInitContext(patternBindingIndex))
+    dc = initContext;
+
   auto result = forInitialization(
       initializer, dc, patternType,
       patternBinding->getPattern(patternBindingIndex), bindPatternVarsOneWay);

lib/Sema/TypeCheckConstraints.cpp

@@ -805,7 +805,7 @@ bool TypeChecker::typeCheckBinding(Pattern *&pattern, Expr *&initializer,
                                    TypeCheckExprOptions options) {
   SyntacticElementTarget target =
       PBD ? SyntacticElementTarget::forInitialization(
-                initializer, DC, patternType, PBD, patternNumber,
+                initializer, patternType, PBD, patternNumber,
                 /*bindPatternVarsOneWay=*/false)
           : SyntacticElementTarget::forInitialization(
                 initializer, DC, patternType, pattern,