[Constraint solver] Make DeclContext explicit. NFC

Author: DougGregor

lib/Sema/CSSolver.cpp

@@ -591,7 +591,7 @@ bool ConstraintSystem::Candidate::solve(
   cs.Timer.emplace(E, cs);
 
   // Generate constraints for the new system.
-  if (auto generatedExpr = cs.generateConstraints(E)) {
+  if (auto generatedExpr = cs.generateConstraints(E, DC)) {
     E = generatedExpr;
   } else {
     // Failure to generate constraint system for sub-expression
@@ -1215,7 +1215,7 @@ ConstraintSystem::solveImpl(Expr *&expr,
   shrink(expr);
 
   // Generate constraints for the main system.
-  if (auto generatedExpr = generateConstraints(expr))
+  if (auto generatedExpr = generateConstraints(expr, DC))
     expr = generatedExpr;
   else {
     if (listener)

lib/Sema/ConstraintSystem.h

@@ -3078,7 +3078,7 @@ class ConstraintSystem {
   /// Generate constraints for the given (unchecked) expression.
   ///
   /// \returns a possibly-sanitized expression, or null if an error occurred.
-  Expr *generateConstraints(Expr *E, DeclContext *dc = nullptr);
+  Expr *generateConstraints(Expr *E, DeclContext *dc);
 
   /// Generate constraints for binding the given pattern to the
   /// value of the given expression.

lib/Sema/TypeCheckConstraints.cpp

@@ -2466,7 +2466,7 @@ getTypeOfCompletionOperatorImpl(DeclContext *DC, Expr *expr,
 
   // Construct a constraint system from this expression.
   ConstraintSystem CS(DC, options);
-  expr = CS.generateConstraints(expr);
+  expr = CS.generateConstraints(expr, DC);
   if (!expr)
     return nullptr;