Merge pull request #39399 from xedin/result-builder-switch

[TypeChecker] Prevent pattern resolution from triggering type-checking for unresolved references

Author: xedin

lib/Sema/BuilderTransform.cpp

@@ -1661,6 +1661,14 @@ Optional<BraceStmt *> TypeChecker::applyResultBuilderBodyTransform(
   // Build a constraint system in which we can check the body of the function.
   ConstraintSystem cs(func, options);
 
+  if (cs.isDebugMode()) {
+    auto &log = llvm::errs();
+
+    log << "--- Applying result builder to function ---\n";
+    func->dump(log);
+    log << '\n';
+  }
+
   if (auto result = cs.matchResultBuilder(
           func, builderType, resultContextType, resultConstraintKind,
           cs.getConstraintLocator(func->getBody()))) {

lib/Sema/TypeCheckPattern.cpp

@@ -84,9 +84,7 @@ filterForEnumElement(DeclContext *DC, SourceLoc UseLoc,
   for (const LookupResultEntry &result : foundElements) {
     ValueDecl *e = result.getValueDecl();
     assert(e);
-    if (e->isInvalid()) {
-      continue;
-    }
+
     // Skip if the enum element was referenced as an instance member
     if (unqualifiedLookup) {
       if (!result.getBaseDecl() ||
@@ -96,8 +94,10 @@ filterForEnumElement(DeclContext *DC, SourceLoc UseLoc,
     }
 
     if (auto *oe = dyn_cast<EnumElementDecl>(e)) {
-      // Ambiguities should be ruled out by parsing.
-      assert(!foundElement && "ambiguity in enum case name lookup?!");
+      // Note that there could be multiple elements with the same
+      // name, such results in a re-declaration error, so let's
+      // just always pick the last element, just like in `foundConstant`
+      // case.
       foundElement = oe;
       continue;
     }

test/Constraints/result_builder.swift

@@ -582,6 +582,26 @@ func testSwitch(_ e: E) {
   }
 }
 
+func testExistingPatternsInCaseStatements() {
+  tuplify(true) { c in
+    switch false {
+    case (c): 1 // Ok
+    default:  0
+    }
+  }
+
+  var arr: [Int] = []
+
+  tuplify(true) { c in
+    let n = arr.endIndex
+
+    switch arr.startIndex {
+    case (n): 1 // Ok
+    default:  0
+    }
+  }
+}
+
 // CHECK: testSwitch
 // CHECK-SAME: first(main.Either<Swift.String, (Swift.Int, Swift.String)>.first("a"))
 testSwitch(getE(0))