[clang] [clang-format] Fix RemoveSemicolon for empty ctors/dtors (PR #82278)

[Owen Pan via cfe-commits]

https://github.com/owenca created https://github.com/llvm/llvm-project/pull/82278

Fixes #79833.

>From 4bcf6dba8b97096801be550c4a8d1626ed57e475 Mon Sep 17 00:00:00 2001
From: Owen Pan <owenpiano at gmail.com>
Date: Mon, 19 Feb 2024 13:11:29 -0800
Subject: [PATCH] [clang-format] Fix RemoveSemicolon for empty ctors/dtors

Fixes #79833.
---
 clang/lib/Format/Format.cpp           | 23 ++++++++++++++++-------
 clang/unittests/Format/FormatTest.cpp | 19 +++++++++++++------
 2 files changed, 29 insertions(+), 13 deletions(-)

diff --git a/clang/lib/Format/Format.cpp b/clang/lib/Format/Format.cpp
index e67b2101f5821b..d6ecb3ecad1f9b 100644
--- a/clang/lib/Format/Format.cpp
+++ b/clang/lib/Format/Format.cpp
@@ -2261,27 +2261,36 @@ class SemiRemover : public TokenAnalyzer {
           FormatTokenLexer &Tokens) override {
     AffectedRangeMgr.computeAffectedLines(AnnotatedLines);
     tooling::Replacements Result;
-    removeSemi(AnnotatedLines, Result);
+    removeSemi(Annotator, AnnotatedLines, Result);
     return {Result, 0};
   }
 
 private:
-  void removeSemi(SmallVectorImpl<AnnotatedLine *> &Lines,
+  void removeSemi(TokenAnnotator &Annotator,
+                  SmallVectorImpl<AnnotatedLine *> &Lines,
                   tooling::Replacements &Result) {
+    auto PrecededByFunctionRBrace = [](const FormatToken &Tok) {
+      const auto *Prev = Tok.Previous;
+      if (!Prev || Prev->isNot(tok::r_brace))
+        return false;
+      const auto *LBrace = Prev->MatchingParen;
+      return LBrace && LBrace->is(TT_FunctionLBrace);
+    };
     const auto &SourceMgr = Env.getSourceManager();
     const auto End = Lines.end();
     for (auto I = Lines.begin(); I != End; ++I) {
       const auto Line = *I;
-      removeSemi(Line->Children, Result);
+      removeSemi(Annotator, Line->Children, Result);
       if (!Line->Affected)
         continue;
+      Annotator.calculateFormattingInformation(*Line);
       const auto NextLine = I + 1 == End ? nullptr : I[1];
       for (auto Token = Line->First; Token && !Token->Finalized;
            Token = Token->Next) {
-        if (!Token->Optional)
-          continue;
-        if (Token->isNot(tok::semi))
+        if (Token->isNot(tok::semi) ||
+            (!Token->Optional && !PrecededByFunctionRBrace(*Token))) {
           continue;
+        }
         auto Next = Token->Next;
         assert(Next || Token == Line->Last);
         if (!Next && NextLine)
@@ -3677,7 +3686,7 @@ reformat(const FormatStyle &Style, StringRef Code,
       FormatStyle S = Expanded;
       S.RemoveSemicolon = true;
       Passes.emplace_back([&, S = std::move(S)](const Environment &Env) {
-        return SemiRemover(Env, S).process(/*SkipAnnotation=*/true);
+        return SemiRemover(Env, S).process();
       });
     }
 
diff --git a/clang/unittests/Format/FormatTest.cpp b/clang/unittests/Format/FormatTest.cpp
index d9e369296eed16..b60f1e27e30b0c 100644
--- a/clang/unittests/Format/FormatTest.cpp
+++ b/clang/unittests/Format/FormatTest.cpp
@@ -26707,13 +26707,20 @@ TEST_F(FormatTest, RemoveSemicolon) {
 
   verifyIncompleteFormat("class C final [[deprecated(l]] {});", Style);
 
-  // These tests are here to show a problem that may not be easily
-  // solved, our implementation to remove semicolons is only as good
-  // as our FunctionLBrace detection and this fails for empty braces
-  // because we can't distringuish this from a bracelist.
-  // We will enable when that is resolved.
-#if 0
   verifyFormat("void main() {}", "void main() {};", Style);
+
+  verifyFormat("struct Foo {\n"
+               "  Foo() {}\n"
+               "  ~Foo() {}\n"
+               "};",
+               "struct Foo {\n"
+               "  Foo() {};\n"
+               "  ~Foo() {};\n"
+               "};",
+               Style);
+
+// We can't (and probably shouldn't) support the following.
+#if 0
   verifyFormat("void foo() {} //\n"
                "int bar;",
                "void foo() {}; //\n"