[Sema] Generate completion fix-its for C code as well

[yvvan]

Summary

Current completion fix-its approach does not provide OtherOpBase for C code. But we can easily proceed in this case taking the original Base type.

[yvvan]

Test is added

[ilya-biryukov]

It's the responsibility of the caller to provide a corrected expression, this keeps the completion function simpler. I suggest we stick to this contract.
We do something in getLangOpts().CPlusPlus case to create a corrected expression, let's just implement a similar fallback for C at the single callsite that we have (ParsePostfixExpressionSuffix).

[yvvan]

I tried that first but did not I find a way just to copy an expression (we basically need the same expr for such case). Do you know how to properly generate a copy of expression or some other way to get the same expression?

[ilya-biryukov]

In D52261#1240143, @yvvan wrote:

I tried that first but did not I find a way just to copy an expression (we basically need the same expr for such case). Do you know how to properly generate a copy of expression or some other way to get the same expression?

It seems Sema::ActOnStartCXXMemberReference only changes expression when overloading for C++'s operator -> is required, otherwise it keeps the same expression. Since C does not have that, we can just leave the expression as is.
So setting CorrectedLHS = LHS for C should do the trick (no need to copy the expression IIUC, it's fine to use the same pointer for both CorrectedLHS and LHS).

[yvvan]

You're right actually. The fix is much simpler than I expected :)

[yvvan]

Provide CorrectedBase = Base for C code

[ilya-biryukov]

Thanks! LGTM!

lib/Parse/ParseExpr.cpp

case tok::period: {
           CorrectedLHS = Actions.ActOnStartCXXMemberReference(
               getCurScope(), OrigLHS, OpLoc, CorrectedOpKind, ObjectType,
               MayBePseudoDestructor);
           Diags.setSuppressAllDiagnostics(DiagsAreSuppressed);
         }
 
         Expr *Base = LHS.get();
         Expr *CorrectedBase = CorrectedLHS.get();
+        if (!CorrectedBase && !getLangOpts().CPlusPlus)
+          CorrectedBase = Base;
 
         // Code completion for a member access expression.
         Actions.CodeCompleteMemberReferenceExpr(
             getCurScope(), Base, CorrectedBase, OpLoc, OpKind == tok::arrow,
             Base && ExprStatementTokLoc == Base->getLocStart());
 
         cutOffParsing();
         return ExprError();

test/CodeCompletion/member-access.c

 struct Point {
   float x;
   float y;
   float z;
 };
 
 void test(struct Point *p) {
   p->
   // RUN: %clang_cc1 -fsyntax-only -code-completion-at=%s:8:6 %s -o - | FileCheck -check-prefix=CHECK-CC1 %s
   // CHECK-CC1: x
   // CHECK-CC1: y
   // CHECK-CC1: z
+}
+
+struct Point2 {
+  float x;
+};
+
+void test2(struct Point2 p) {
+  p->
+}
+
+void test3(struct Point2 *p) {
+  p.
+}
+
+// RUN: %clang_cc1 -fsyntax-only -code-completion-with-fixits -code-completion-at=%s:20:6 %s -o - | FileCheck -check-prefix=CHECK-CC2 %s
+// CHECK-CC2: x (requires fix-it: {20:4-20:6} to ".")
+
+// RUN: %clang_cc1 -fsyntax-only -code-completion-with-fixits -code-completion-at=%s:24:5 %s -o - | FileCheck -check-prefix=CHECK-CC3 %s
+// CHECK-CC3: x (requires fix-it: {24:4-24:5} to "->")