[TypeChecker] Add a flag PreCheckFunctionBuilderRequest to suppress diagnostics

include/swift/AST/TypeCheckRequests.h

@@ -1843,6 +1843,7 @@ public:
 
 struct PreCheckFunctionBuilderDescriptor {
   AnyFunctionRef Fn;
+  bool SuppressDiagnostics;
 
 private:
   // NOTE: Since source tooling (e.g. code completion) might replace the body,
@@ -1852,8 +1853,8 @@ private:
   BraceStmt *Body;
 
 public:
-  PreCheckFunctionBuilderDescriptor(AnyFunctionRef Fn)
-      : Fn(Fn), Body(Fn.getBody()) {}
+  PreCheckFunctionBuilderDescriptor(AnyFunctionRef Fn, bool suppressDiagnostics)
+      : Fn(Fn), SuppressDiagnostics(suppressDiagnostics), Body(Fn.getBody()) {}
 
   friend llvm::hash_code
   hash_value(const PreCheckFunctionBuilderDescriptor &owner) {

lib/Sema/BuilderTransform.cpp

@@ -1485,9 +1485,11 @@ Optional<BraceStmt *> TypeChecker::applyFunctionBuilderBodyTransform(
   // If we encountered an error or there was an explicit result type,
   // bail out and report that to the caller.
   auto &ctx = func->getASTContext();
-  auto request = PreCheckFunctionBuilderRequest{AnyFunctionRef(func)};
-  switch (evaluateOrDefault(
-              ctx.evaluator, request, FunctionBuilderBodyPreCheck::Error)) {
+  auto request =
+      PreCheckFunctionBuilderRequest{{AnyFunctionRef(func),
+                                      /*SuppressDiagnostics=*/false}};
+  switch (evaluateOrDefault(ctx.evaluator, request,
+                            FunctionBuilderBodyPreCheck::Error)) {
   case FunctionBuilderBodyPreCheck::Okay:
     // If the pre-check was okay, apply the function-builder transform.
     break;
@@ -1619,7 +1621,8 @@ ConstraintSystem::matchFunctionBuilder(
 
   // Pre-check the body: pre-check any expressions in it and look
   // for return statements.
-  auto request = PreCheckFunctionBuilderRequest{fn};
+  auto request =
+      PreCheckFunctionBuilderRequest{{fn, /*SuppressDiagnostics=*/false}};
   switch (evaluateOrDefault(getASTContext().evaluator, request,
                             FunctionBuilderBodyPreCheck::Error)) {
   case FunctionBuilderBodyPreCheck::Okay:
@@ -1705,14 +1708,17 @@ namespace {
 class PreCheckFunctionBuilderApplication : public ASTWalker {
   AnyFunctionRef Fn;
   bool SkipPrecheck = false;
+  bool SuppressDiagnostics = false;
   std::vector<ReturnStmt *> ReturnStmts;
   bool HasError = false;
 
   bool hasReturnStmt() const { return !ReturnStmts.empty(); }
 
 public:
-  PreCheckFunctionBuilderApplication(AnyFunctionRef fn, bool skipPrecheck)
-      : Fn(fn), SkipPrecheck(skipPrecheck) {}
+  PreCheckFunctionBuilderApplication(AnyFunctionRef fn, bool skipPrecheck,
+                                     bool suppressDiagnostics)
+      : Fn(fn), SkipPrecheck(skipPrecheck),
+        SuppressDiagnostics(suppressDiagnostics) {}
 
   const std::vector<ReturnStmt *> getReturnStmts() const { return ReturnStmts; }
 
@@ -1753,7 +1759,9 @@ public:
           E, DC, /*replaceInvalidRefsWithErrors=*/false);
       HasError |= transaction.hasDiagnostics();
 
+      if (SuppressDiagnostics)
         transaction.abort();
+
       return std::make_pair(false, HasError ? nullptr : E);
     }
   }
@@ -1788,11 +1796,15 @@ FunctionBuilderBodyPreCheck PreCheckFunctionBuilderRequest::evaluate(
           owner.Fn.getAbstractClosureExpr()))
     skipPrecheck = shouldTypeCheckInEnclosingExpression(closure);
 
-  return PreCheckFunctionBuilderApplication(owner.Fn, false).run();
+  return PreCheckFunctionBuilderApplication(
+             owner.Fn, /*skipPrecheck=*/false,
+             /*suppressDiagnostics=*/owner.SuppressDiagnostics)
+      .run();
 }
 
 std::vector<ReturnStmt *> TypeChecker::findReturnStatements(AnyFunctionRef fn) {
-  PreCheckFunctionBuilderApplication precheck(fn, true);
+  PreCheckFunctionBuilderApplication precheck(fn, /*skipPreCheck=*/true,
+                                              /*SuppressDiagnostics=*/true);
   (void)precheck.run();
   return precheck.getReturnStmts();
 }