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

[Owen Pan via cfe-commits]

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

>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 1/2] [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);

>From cd9b3d77210c9612c1ac513c10a583d50f168096 Mon Sep 17 00:00:00 2001
From: Owen Pan <owenpiano at gmail.com>
Date: Wed, 1 Nov 2023 12:23:25 -0700
Subject: [PATCH 2/2] Added test cases with comments before the semicolon

---
 clang/unittests/Format/FormatTest.cpp | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/clang/unittests/Format/FormatTest.cpp b/clang/unittests/Format/FormatTest.cpp
index 4c09a7eb106e79e..80903e7630c8073 100644
--- a/clang/unittests/Format/FormatTest.cpp
+++ b/clang/unittests/Format/FormatTest.cpp
@@ -1362,6 +1362,7 @@ TEST_F(FormatTest, FormatLoopsWithoutCompoundStatement) {
 
   FormatStyle AllowsMergedLoops = getLLVMStyle();
   AllowsMergedLoops.AllowShortLoopsOnASingleLine = true;
+
   verifyFormat("while (true) continue;", AllowsMergedLoops);
   verifyFormat("for (;;) continue;", AllowsMergedLoops);
   verifyFormat("for (int &v : vec) v *= 2;", AllowsMergedLoops);
@@ -1405,6 +1406,7 @@ TEST_F(FormatTest, FormatLoopsWithoutCompoundStatement) {
                "  a++;\n"
                "while (true);",
                AllowsMergedLoops);
+
   // Without braces labels are interpreted differently.
   verifyFormat("{\n"
                "  do\n"
@@ -1413,6 +1415,17 @@ TEST_F(FormatTest, FormatLoopsWithoutCompoundStatement) {
                "  while (true);\n"
                "}",
                AllowsMergedLoops);
+
+  // Don't merge if there are comments before the null statement.
+  verifyFormat("while (1) //\n"
+               "  ;",
+               AllowsMergedLoops);
+  verifyFormat("for (;;) /**/\n"
+               "  ;",
+               AllowsMergedLoops);
+  verifyFormat("while (true) /**/\n"
+               "  ;",
+               "while (true) /**/;", AllowsMergedLoops);
 }
 
 TEST_F(FormatTest, FormatShortBracedStatements) {