[Sema] Correctly diagnose passing tuple as only argument to function with multiple parameters

If a tuple is passed as the only argument to a function that takes two unnamed arguments, we try to diagnose the missing argument label. However, in the old diagnose code we didn’t distinguish between non-existing arguments and arguments without labels; both behaved the same.

Thus, the missing second argument in the function call would line up with the empty second argument label, not producing a diagnostic, but hitting an assertion later on.

Distinguish between the two to fix the issue.

Fixes rdar://64319340

Author: ahoppen

lib/Sema/MiscDiagnostics.cpp

@@ -1847,28 +1847,45 @@ bool swift::diagnoseArgumentLabelError(ASTContext &ctx,
   llvm::SmallString<16> missingBuffer;
   llvm::SmallString<16> extraBuffer;
   for (unsigned i = 0; i != n; ++i) {
-    Identifier oldName;
+    // oldName and newName are
+    //  - None if i is out of bounds for the argument list
+    //  - nullptr for an argument without a label
+    //  - have a value if the argument has a label
+    Optional<Identifier> oldName;
     if (i < argList.args.size())
       oldName = argList.labels[i];
-    Identifier newName;
+    Optional<Identifier> newName;
     if (i < newNames.size())
       newName = newNames[i];
 
+    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 &&
+        (argList.hasTrailingClosure && i == argList.args.size() - 1 &&
          (numMissing > 0 || numExtra > 0 || numWrong > 0)))
       continue;
 
-    if (oldName.empty()) {
+    if (!oldName.hasValue() && newName.hasValue()) {
+      ++numMissing;
+      missingBuffer += newName->str();
+      missingBuffer += ':';
+    } else if (oldName.hasValue() && !newName.hasValue()) {
+      ++numExtra;
+      extraBuffer += oldName->str();
+      extraBuffer += ':';
+    } else if (oldName->empty()) {
+      // In the cases from here onwards oldValue and newValue are not null
       ++numMissing;
-      missingBuffer += newName.str();
+      missingBuffer += newName->str();
       missingBuffer += ":";
-    } else if (newName.empty()) {
+    } else if (newName->empty()) {
       ++numExtra;
-      extraBuffer += oldName.str();
+      extraBuffer += oldName->str();
       extraBuffer += ':';
-    } else
+    } else {
       ++numWrong;
+    }
   }
 
   // Emit the diagnostic.

test/Constraints/argument_matching.swift

@@ -1086,7 +1086,7 @@ func testUnlabeledParameterBindingPosition() {
     func f(aa: Int, bb: Int, _ cc: Int) {}
 
     f(0, 2)
-    // expected-error@-1:6 {{missing argument labels 'aa:bb:' in call}}
+    // expected-error@-1:6 {{missing argument labels 'aa:bb::' in call}}
     // expected-error@-2:8 {{missing argument for parameter 'bb' in call}}
 
     f(0, bb: 1, 2)
@@ -1191,7 +1191,7 @@ func testUnlabeledParameterBindingPosition() {
     // expected-error@-1:6 {{missing arguments for parameters 'aa', 'cc' in call}}
 
     f(1, 2, 3)
-    // expected-error@-1 {{missing argument labels 'aa:cc:' in call}}
+    // expected-error@-1 {{missing argument labels 'aa:cc::' in call}}
     // expected-error@-2:11 {{missing argument for parameter 'cc' in call}}
 
     f(1, 2, 3, 4)
@@ -1223,7 +1223,7 @@ func testUnlabeledParameterBindingPosition() {
     // expected-error@-1:12 {{missing argument for parameter 'bb' in call}}
 
     f(aa: 1, xx: 2, 3)
-    // expected-error@-1 {{incorrect argument label in call (have 'aa:xx:_:', expected 'aa:bb:_:_:')}}
+    // expected-error@-1 {{incorrect argument labels in call (have 'aa:xx:_:', expected 'aa:bb:_:_:')}}
     // expected-error@-2:12 {{missing argument for parameter 'bb' in call}}
 
     f(aa: 1, bb: 2, 3, xx: 4)

test/Sema/call_function_with_tuple.swift

@@ -0,0 +1,11 @@
+// RUN: %target-typecheck-verify-swift
+
+func twoArgs(_ a: Int, _ b: Int) -> Void { //expected-note{{'twoArgs' declared here}}
+}
+
+func call() {
+  // Call a function that takes two unnamed arguments with a tuple that has two
+  // named arguments
+  let namedTuple: (x: Int, y: Int) = (1, 1)
+  twoArgs(namedTuple) // expected-error{{global function 'twoArgs' expects 2 separate arguments}} expected-error{{missing argument label ':' in call}}
+}