[clang] [clang-format] Break after string literals with trailing line breaks (PR #76795)

[kadir çetinkaya via cfe-commits]

https://github.com/kadircet created https://github.com/llvm/llvm-project/pull/76795

This restores a subset of functionality that was forego in
d68826dfbd987377ef6771d40c1d984f09ee3b9e.

Streaming multiple string literals is rare enough in practice, hence
that change makes sense in general. But it seems people were
incidentally relying on this for having line breaks after string
literals that ended with `\n`.

This patch tries to restore that behavior to prevent regressions in the
upcoming LLVM release, until we can implement some configuration based
approach as proposed in https://github.com/llvm/llvm-project/pull/69859.


>From b09c89ee1dc88e030040bcf30063ea16ec5a0b58 Mon Sep 17 00:00:00 2001
From: Kadir Cetinkaya <kadircet at google.com>
Date: Wed, 3 Jan 2024 09:28:35 +0100
Subject: [PATCH] [clang-format] Break after string literals with trailing line
 breaks

This restores a subset of functionality that was forego in
d68826dfbd987377ef6771d40c1d984f09ee3b9e.

Streaming multiple string literals is rare enough in practice, hence
that change makes sense in general. But it seems people were
incidentally relying on this for having line breaks after string
literals that ended with `\n`.

This patch tries to restore that behavior to prevent regressions in the
upcoming LLVM release, until we can implement some configuration based
approach as proposed in https://github.com/llvm/llvm-project/pull/69859.
---
 clang/lib/Format/TokenAnnotator.cpp           |  8 ++++++++
 clang/unittests/Format/TokenAnnotatorTest.cpp | 10 ++++++++++
 2 files changed, 18 insertions(+)

diff --git a/clang/lib/Format/TokenAnnotator.cpp b/clang/lib/Format/TokenAnnotator.cpp
index 3ac3aa3c5e3a22..27c6bb0ef6fe4f 100644
--- a/clang/lib/Format/TokenAnnotator.cpp
+++ b/clang/lib/Format/TokenAnnotator.cpp
@@ -5151,6 +5151,14 @@ bool TokenAnnotator::mustBreakBefore(const AnnotatedLine &Line,
     return true;
   if (Left.IsUnterminatedLiteral)
     return true;
+  if (Right.is(tok::lessless) && Right.Next && Left.is(tok::string_literal) &&
+      // FIXME: Breaking after newlines seems useful in general. Turn this into
+      // an option and Recognize more cases like endl etc, and break independent
+      // of what comes after operator lessless.
+      Right.Next->is(tok::string_literal) &&
+      Left.TokenText.ends_with("\\n\"")) {
+    return true;
+  }
   if (Right.is(TT_RequiresClause)) {
     switch (Style.RequiresClausePosition) {
     case FormatStyle::RCPS_OwnLine:
diff --git a/clang/unittests/Format/TokenAnnotatorTest.cpp b/clang/unittests/Format/TokenAnnotatorTest.cpp
index 2cafc0438ffb46..cd3ffb611839d2 100644
--- a/clang/unittests/Format/TokenAnnotatorTest.cpp
+++ b/clang/unittests/Format/TokenAnnotatorTest.cpp
@@ -10,6 +10,7 @@
 
 #include "FormatTestUtils.h"
 #include "TestLexer.h"
+#include "clang/Basic/TokenKinds.h"
 #include "gtest/gtest.h"
 
 namespace clang {
@@ -2499,6 +2500,15 @@ TEST_F(TokenAnnotatorTest, BraceKind) {
   EXPECT_BRACE_KIND(Tokens[6], BK_Block);
 }
 
+TEST_F(TokenAnnotatorTest, StreamOperator) {
+  auto Tokens = annotate("\"foo\\n\" << aux << \"foo\\n\" << \"foo\";");
+  ASSERT_EQ(Tokens.size(), 9u) << Tokens;
+  EXPECT_FALSE(Tokens[1]->MustBreakBefore);
+  EXPECT_FALSE(Tokens[3]->MustBreakBefore);
+  // Only break between string literals if the former ends with \n.
+  EXPECT_TRUE(Tokens[5]->MustBreakBefore);
+}
+
 } // namespace
 } // namespace format
 } // namespace clang