[CodeCompletion] Always suggest call pattern for nested function calls

When completing in cases like `bar(arg: foo(|, option: 1)`, we don’t know if `option` belongs to the call to `foo` or `bar`. Be defensive and also suggest the signature.

Author: ahoppen

lib/IDE/ArgumentCompletion.cpp

@@ -284,6 +284,15 @@ void ArgumentTypeCheckCompletionCallback::sawSolutionImpl(const Solution &S) {
     // and the code completion token doesn’t have a label, we have a case like
     // `Point(|)`. Suggest the entire function signature.
     IncludeSignature = true;
+  } else if (!ParentCall->getArgs()->empty() &&
+             ParentCall->getArgs()->getExpr(0) == CompletionExpr) {
+    if (auto ParentExpr = CS.getParentExpr(ParentCall);
+        ParentExpr && CS.getParentExpr(ParentCall)->getArgs()) {
+      // We are completing in cases like `bar(arg: foo(|, option: 1)`
+      // In these cases, we don’t know if `option` belongs to the call to `foo`
+      // or `bar`. Be defensive and also suggest the signature.
+      IncludeSignature = true;
+    }
   }
 
   Results.push_back(

test/IDE/complete_call_arg.swift

@@ -1407,3 +1407,14 @@ struct AtStartOfFunctionCallWithExistingParams {
     // AT_START_OF_CALL_ONE_EXISTING_ARGUMENT-DAG: Pattern/Local/Flair[ArgLabels]:     {#a: Int#}[#Int#]; name=a:
   }
 }
+
+func nestedCallsWithoutClosingParen() {
+  func foo(arg: Int, arg2: Int) -> Int { 1 }
+  func bar(arg: Int, option: Int) -> Int { 1 }
+
+  bar(arg: foo(#^NESTED_CALL_AT_START^#, option: 1)
+  // NESTED_CALL_AT_START-DAG: Decl[FreeFunction]/Local/Flair[ArgLabels]/TypeRelation[Convertible]: ['(']{#arg: Int#}, {#arg2: Int#}[')'][#Int#];
+
+  bar(arg: foo(arg: 1, #^NESTED_CALL_AT_SECOND_ARG^#, option: 1)
+  // NESTED_CALL_AT_SECOND_ARG-DAG: Pattern/Local/Flair[ArgLabels]:     {#arg2: Int#}[#Int#];
+}