[CS] Better handle unsupported result builder elements for completion

Instead of failing, fall back to solving as a regular function body.

rdar://144303920

Author: hamishknight

lib/Sema/BuilderTransform.cpp

@@ -269,12 +269,7 @@ class ResultBuilderTransform
     for (auto element : braceStmt->getElements()) {
       if (auto unsupported =
               transformBraceElement(element, newBody, buildBlockArguments)) {
-        // When in code completion mode, simply ignore unsported constructs to
-        // get results for anything that's unrelated to the unsupported
-        // constructs.
-        if (!ctx.CompletionCallback) {
-          return failTransform(*unsupported);
-        }
+        return failTransform(*unsupported);
       }
     }
 
@@ -1156,18 +1151,17 @@ ConstraintSystem::matchResultBuilder(AnyFunctionRef fn, Type builderType,
     auto *body = transform.apply(fn.getBody());
 
     if (auto unsupported = transform.getUnsupportedElement()) {
-      assert(!body || getASTContext().CompletionCallback);
-
-      // If we aren't supposed to attempt fixes, fail.
-      if (!shouldAttemptFixes()) {
-        return getTypeMatchFailure(locator);
-      }
+      assert(!body);
 
       // If we're solving for code completion and the body contains the code
-      // completion location, skipping it won't get us to a useful solution so
-      // just bail.
+      // completion location, fall back to solving as a regular function body.
       if (isForCodeCompletion() &&
           containsIDEInspectionTarget(fn.getBody())) {
+        return std::nullopt;
+      }
+
+      // If we aren't supposed to attempt fixes, fail.
+      if (!shouldAttemptFixes()) {
         return getTypeMatchFailure(locator);
       }
 

test/IDE/complete_in_result_builder.swift

@@ -53,6 +53,12 @@ func testGlobalLookup() {
     }
   }
 
+  buildStringTuple {
+    if {
+      #^GLOBAL_LOOKUP_IN_IF_BODY_WITHOUT_CONDITION_CLOSURE?check=GLOBAL_LOOKUP_IN_IF_BODY^#
+    }
+  }
+
   @TupleBuilder<String> var x4 {
     guard else {
       #^GLOBAL_LOOKUP_IN_GUARD_BODY_WITHOUT_CONDITION?check=GLOBAL_LOOKUP_IN_IF_BODY^#
@@ -146,6 +152,11 @@ func testPatternMatching() {
     let x: FooStruct? = FooStruct()
     guard case .#^GUARD_CASE_PATTERN_2?check=OPTIONAL_FOOSTRUCT^#some() = x {}
   }
+
+  buildStringTuple {
+    let x: FooStruct? = FooStruct()
+    guard case .#^GUARD_CASE_PATTERN_3?check=OPTIONAL_FOOSTRUCT^#some() = x {}
+  }
 }
 
 func testCompleteFunctionArgumentLabels() {
@@ -428,3 +439,24 @@ func testInForLoop(_ x: [Int]) {
     }
   }
 }
+
+func testUnsupportedForLoop() {
+  @resultBuilder
+  struct Builder {
+    static func buildBlock<T>(_ components: T...) -> T {
+      components.first!
+    }
+  }
+
+  func foo(@Builder fn: () -> Int) {}
+
+  foo {
+    for i in [0].#^COMPLETE_IN_UNSUPPORTED_FOR^# {}
+  }
+  // COMPLETE_IN_UNSUPPORTED_FOR: Decl[InstanceVar]/Super/IsSystem: first[#Int?#]; name=first
+
+  foo {
+    for i in [0].#^COMPLETE_IN_UNSUPPORTED_FOR_2?check=COMPLETE_IN_UNSUPPORTED_FOR^# {}
+    return 0
+  }
+}