[Sema] Correct label fix-its for multiple trailing closures

Update the logic to account for multiple trailing
closures.

rdar://81278194

Author: hamishknight

lib/Sema/MiscDiagnostics.cpp

@@ -1906,9 +1906,7 @@ bool swift::diagnoseArgumentLabelError(ASTContext &ctx,
     assert(oldName || newName && "We can't have oldName and newName out of "
                                  "bounds, otherwise n would be smaller");
 
-    if (oldName == newName ||
-        (argList.hasTrailingClosure && i == argList.args.size() - 1 &&
-         (numMissing > 0 || numExtra > 0 || numWrong > 0)))
+    if (oldName == newName || argList.isUnlabeledTrailingClosureIdx(i))
       continue;
 
     if (!oldName.hasValue() && newName.hasValue()) {
@@ -1988,11 +1986,17 @@ bool swift::diagnoseArgumentLabelError(ASTContext &ctx,
     if (i < newNames.size())
       newName = newNames[i];
 
-    if (oldName == newName || (i == n-1 && argList.hasTrailingClosure))
+    if (oldName == newName || argList.isUnlabeledTrailingClosureIdx(i))
       continue;
 
     if (newName.empty()) {
-      // Delete the old name.
+      // If this is a labeled trailing closure, we need to replace with '_'.
+      if (argList.isLabeledTrailingClosureIdx(i)) {
+        diag.fixItReplace(argList.labelLocs[i], "_");
+        continue;
+      }
+
+      // Otherwise, delete the old name.
       diag.fixItRemoveChars(argList.labelLocs[i],
                             argList.args[i]->getStartLoc());
       continue;
@@ -2006,7 +2010,10 @@ bool swift::diagnoseArgumentLabelError(ASTContext &ctx,
     if (newNameIsReserved)
       newStr += "`";
 
-    if (oldName.empty()) {
+    // If the argument was previously unlabeled, insert the new label. Note that
+    // we don't do this for labeled trailing closures as they write unlabeled
+    // args as '_:', and therefore need replacement.
+    if (oldName.empty() && !argList.isLabeledTrailingClosureIdx(i)) {
       // Insert the name.
       newStr += ": ";
       diag.fixItInsert(argList.args[i]->getStartLoc(), newStr);

test/Parse/trailing_closures.swift

@@ -82,7 +82,7 @@ func test_multiple_trailing_syntax_without_labels() {
 
   fn {} g: {} // Ok
 
-  fn {} _: {} // expected-error {{missing argument labels 'f:g:' in call}}
+  fn {} _: {} // expected-error {{missing argument label 'g:' in call}} {{9-10=g}} {{none}}
 
   fn {} g: <#T##() -> Void#> // expected-error {{editor placeholder in source file}}
 
@@ -95,14 +95,13 @@ func test_multiple_trailing_syntax_without_labels() {
 
   mixed_args_1 {} _: {}
 
-  mixed_args_1 {} a: {}  // expected-error@:16 {{incorrect argument labels in call (have '_:a:', expected 'a:_:')}}
+  mixed_args_1 {} a: {}  // expected-error@:16 {{extraneous argument label 'a:' in call}} {{19-20=_}} {{none}}
 
   mixed_args_2 {} a: {} _: {}
 
-  mixed_args_2 {} _: {} // expected-error@:18 {{missing argument for parameter 'a' in call}}
+  mixed_args_2 {} _: {} // expected-error@:18 {{missing argument for parameter 'a' in call}} {{18-18= a: <#() -> Void#>}} {{none}}
 
-  // FIXME: not a good diagnostic
-  mixed_args_2 {} _: {} _: {} // expected-error@:16 {{missing argument label 'a:' in call}}
+  mixed_args_2 {} _: {} _: {} // expected-error@:16 {{missing argument label 'a:' in call}} {{19-20=a}} {{none}}
 }
 
 func produce(fn: () -> Int?, default d: () -> Int) -> Int { // expected-note {{declared here}}