[clang] [clang-format] Treat empty for/while loops as short loops (PR #70768)

[Owen Pan via cfe-commits]

https://github.com/owenca created https://github.com/llvm/llvm-project/pull/70768

A for/while loop with only a semicolon as its body should be treated as an empty loop.

Fixes #61708.

>From 7e6030532f99b4128807631e993609ce40171043 Mon Sep 17 00:00:00 2001
From: Owen Pan <owenpiano at gmail.com>
Date: Mon, 30 Oct 2023 22:50:27 -0700
Subject: [PATCH] [clang-format] Treat empty for/while loops as short loops

A for/while loop with only a semicolon as its body should be treated as an
empty loop.

Fixes #61708.
---
 clang/lib/Format/UnwrappedLineParser.cpp | 11 +++++++++--
 clang/unittests/Format/FormatTest.cpp    | 13 +++++++------
 2 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/clang/lib/Format/UnwrappedLineParser.cpp b/clang/lib/Format/UnwrappedLineParser.cpp
index 30f9bcbfa29308e..94e238039c2a707 100644
--- a/clang/lib/Format/UnwrappedLineParser.cpp
+++ b/clang/lib/Format/UnwrappedLineParser.cpp
@@ -3117,9 +3117,16 @@ void UnwrappedLineParser::parseForOrWhileLoop(bool HasParens) {
       FormatTok->setFinalizedType(TT_ConditionLParen);
     parseParens();
   }
-  // Event control.
-  if (Style.isVerilog())
+
+  if (Style.isVerilog()) {
+    // Event control.
     parseVerilogSensitivityList();
+  } else if (Style.AllowShortLoopsOnASingleLine && FormatTok->is(tok::semi) &&
+             Tokens->getPreviousToken()->is(tok::r_paren)) {
+    nextToken();
+    addUnwrappedLine();
+    return;
+  }
 
   handleAttributes();
   parseLoopBody(KeepBraces, /*WrapRightBrace=*/true);
diff --git a/clang/unittests/Format/FormatTest.cpp b/clang/unittests/Format/FormatTest.cpp
index 15c12c2b8b0da3f..4c09a7eb106e79e 100644
--- a/clang/unittests/Format/FormatTest.cpp
+++ b/clang/unittests/Format/FormatTest.cpp
@@ -1355,18 +1355,19 @@ TEST_F(FormatTest, FormatIfWithoutCompoundStatementButElseWith) {
 }
 
 TEST_F(FormatTest, FormatLoopsWithoutCompoundStatement) {
+  verifyFormat("while (true)\n"
+               "  ;");
+  verifyFormat("for (;;)\n"
+               "  ;");
+
   FormatStyle AllowsMergedLoops = getLLVMStyle();
   AllowsMergedLoops.AllowShortLoopsOnASingleLine = true;
   verifyFormat("while (true) continue;", AllowsMergedLoops);
   verifyFormat("for (;;) continue;", AllowsMergedLoops);
   verifyFormat("for (int &v : vec) v *= 2;", AllowsMergedLoops);
   verifyFormat("BOOST_FOREACH (int &v, vec) v *= 2;", AllowsMergedLoops);
-  verifyFormat("while (true)\n"
-               "  ;",
-               AllowsMergedLoops);
-  verifyFormat("for (;;)\n"
-               "  ;",
-               AllowsMergedLoops);
+  verifyFormat("while (true);", AllowsMergedLoops);
+  verifyFormat("for (;;);", AllowsMergedLoops);
   verifyFormat("for (;;)\n"
                "  for (;;) continue;",
                AllowsMergedLoops);