[CodeCompletion] Don't typecheck expression if result builder transform was applied

Author: ahoppen

lib/Sema/TypeCheckStmt.cpp

@@ -2587,18 +2587,22 @@ bool TypeCheckASTNodeAtLocRequest::evaluate(
           func, builderType,
           /*ClosuresInResultBuilderDontParticipateInInference=*/
               ctx.CompletionCallback == nullptr && ctx.SolutionCallback == nullptr);
-      if (optBody && *optBody) {
+      if (ctx.CompletionCallback && ctx.CompletionCallback->gotCallback()) {
+        // We already informed the completion callback of solutions found by
+        // type checking the entire result builder from
+        // applyResultBuilderBodyTransform. No need to typecheck the requested
+        // AST node individually anymore.
+        return false;
+      }
+      if (!ctx.CompletionCallback && !ctx.SolutionCallback && optBody && *optBody) {
         // Wire up the function body now.
         func->setBody(*optBody, AbstractFunctionDecl::BodyKind::TypeChecked);
         return false;
       }
-      // FIXME: We failed to apply the result builder transform. Fall back to
-      // just type checking the node that contains the code completion token.
-      // This may be missing some context from the result builder but in
-      // practice it often contains sufficient information to provide a decent
-      // level of code completion that's better than providing nothing at all.
-      // The proper solution would be to only partially type check the result
-      // builder so that this fall back would not be necessary.
+      // We did not find a solution while applying the result builder, possibly
+      // because the result builder contained an invalid element and thus the
+      // transform couldn't be applied. Perform code completion pretending there
+      // was no result builder to recover.
     } else if (func->hasSingleExpressionBody() &&
                 func->getResultInterfaceType()->isVoid()) {
        // The function returns void.  We don't need an explicit return, no matter

test/IDE/complete_in_result_builder.swift

@@ -339,3 +339,24 @@ func testSwitchInResultBuilder() {
 // SWITCH_IN_RESULT_BUILDER: Begin completions, 1 item
 // SWITCH_IN_RESULT_BUILDER-DAG: Decl[EnumElement]/CurrNominal/Flair[ExprSpecific]/TypeRelation[Convertible]: alertDismissed[#Action#];
 }
+
+func testCompleteIfLetInResultBuilder() {
+  func takeClosure(_ x: () -> Void) -> Int {
+    return 0
+  }
+
+  @resultBuilder struct MyResultBuilder {
+    static func buildBlock() -> Int { return 0 }
+    static func buildBlock(_ content: Int) -> Int { content }
+  }
+
+  @MyResultBuilder func test(integer: Int?) -> Int {
+    takeClosure {
+      if let #^IF_LET_IN_RESULT_BUILDER^#integer = integer {
+      }
+    }
+    // IF_LET_IN_RESULT_BUILDER: Begin completions, 1 items
+    // IF_LET_IN_RESULT_BUILDER: Decl[LocalVar]/Local:               integer[#Int?#]; name=integer
+    // IF_LET_IN_RESULT_BUILDER: End completions
+  }
+}