[Function builders] Perform syntactic use checks within function builders.

Author: DougGregor

lib/Sema/BuilderTransform.cpp

@@ -16,6 +16,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "ConstraintSystem.h"
+#include "MiscDiagnostics.h"
 #include "SolutionResult.h"
 #include "TypeChecker.h"
 #include "swift/AST/ASTVisitor.h"
@@ -645,7 +646,7 @@ class BuilderClosureRewriter
   const Solution &solution;
   DeclContext *dc;
   AppliedBuilderTransform builderTransform;
-  std::function<Expr *(Expr *)> rewriteExpr;
+  std::function<Expr *(Expr *)> rewriteExprFn;
   std::function<Expr *(Expr *, Type, ConstraintLocator *)> coerceToType;
 
   /// Retrieve the temporary variable that will be used to capture the
@@ -747,6 +748,13 @@ class BuilderClosureRewriter
     elements.push_back(pbd);
   }
 
+  Expr *rewriteExpr(Expr *expr) {
+    Expr *result = rewriteExprFn(expr);
+    if (result)
+      performSyntacticExprDiagnostics(expr, dc, /*isExprStmt=*/false);
+    return result;
+  }
+
 public:
   BuilderClosureRewriter(
       const Solution &solution,
@@ -756,7 +764,7 @@ class BuilderClosureRewriter
       std::function<Expr *(Expr *, Type, ConstraintLocator *)> coerceToType
     ) : ctx(solution.getConstraintSystem().getASTContext()),
         solution(solution), dc(dc), builderTransform(builderTransform),
-        rewriteExpr(rewriteExpr),
+        rewriteExprFn(rewriteExpr),
         coerceToType(coerceToType){ }
 
   Stmt *visitBraceStmt(BraceStmt *braceStmt, FunctionBuilderTarget target,

test/Constraints/function_builder_diags.swift

@@ -256,3 +256,16 @@ struct MyTuplifiedStruct {
     }
   }
 }
+
+// Check that we're performing syntactic use diagnostics/
+func acceptMetatype<T>(_: T.Type) -> Bool { true }
+
+func syntacticUses<T>(_: T) {
+  tuplify(true) { x in
+    if x && acceptMetatype(T) { // expected-error{{expected member name or constructor call after type name}}
+      // expected-note@-1{{use '.self' to reference the type object}}
+      acceptMetatype(T) // expected-error{{expected member name or constructor call after type name}}
+      // expected-note@-1{{use '.self' to reference the type object}}
+    }
+  }
+}