[clang-format] Don't break between string literal operands of <<

[owenca]

Fixes #44363.

[llvmbot]

@llvm/pr-subscribers-clang-format

Author: Owen Pan (owenca)

Changes

Fixes #44363.

---

Full diff: https://github.com/llvm/llvm-project/pull/69871.diff

2 Files Affected:

• (modified) clang/lib/Format/TokenAnnotator.cpp (-4)
• (modified) clang/unittests/Format/FormatTest.cpp (+4)

diff --git a/clang/lib/Format/TokenAnnotator.cpp b/clang/lib/Format/TokenAnnotator.cpp
index 7f85f48de2ed2ed..e185afaa2885123 100644
--- a/clang/lib/Format/TokenAnnotator.cpp
+++ b/clang/lib/Format/TokenAnnotator.cpp
@@ -5118,10 +5118,6 @@ 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) &&
-      Right.Next->is(tok::string_literal)) {
-    return true;
-  }
   if (Right.is(TT_RequiresClause)) {
     switch (Style.RequiresClausePosition) {
     case FormatStyle::RCPS_OwnLine:
diff --git a/clang/unittests/Format/FormatTest.cpp b/clang/unittests/Format/FormatTest.cpp
index 0a87cfc4f1d6af9..0841ea1bcb66fa9 100644
--- a/clang/unittests/Format/FormatTest.cpp
+++ b/clang/unittests/Format/FormatTest.cpp
@@ -26459,6 +26459,10 @@ TEST_F(FormatTest, AllowBreakBeforeNoexceptSpecifier) {
                Style);
 }
 
+TEST_F(FormatTest, StreamOutputOperator) {
+  verifyFormat("std::cout << \"foo\" << \"bar\" << baz;");
+}
+
 } // namespace
 } // namespace test
 } // namespace format

[s1Sharp]

this is good to be respectful. Please, lets check my mr #69859 also

[s1Sharp]

I think adding the possibility of breaking '<<' is a good idea if it's optional, what do u think?

[owenca]

I think adding the possibility of breaking '<<' is a good idea if it's optional, what do u think?

+1, but see also #69859 (comment).

[petrhosek]

We have noticed that after this change, clang-format would behave differently depending on the input formatting.

(I'm using --style="{BasedOnStyle: google, ColumnLimit: 0}" in the examples below.)

For example, if the input is

return os << "ClientEnd<"
          << "test_anonymous::SomeProtocol"
          << ">(" << value.channel().get() << ")";

the output format would be the same before and after this change.

However, if the input is

return os << "ClientEnd<" << "test_anonymous::SomeProtocol" << ">(" << value.channel().get() << ")";

prior to this change we would reformat it as

return os << "ClientEnd<"
          << "test_anonymous::SomeProtocol"
          << ">(" << value.channel().get() << ")";

but after this change we would format it as

return os << "ClientEnd<" << "test_anonymous::SomeProtocol" << ">(" << value.channel().get() << ")";

that is the same as input.

Is that behavior intentional?

[owenca]

IMO, the new behavior is consistent with the documentation for ColumnLimt: 0.

[mydeveloperday]

I wish we'd made this removal an option rather than just removing it, what we are seeing is reasonably formatted json or xml being streamed out is now poorly written

osjson << "{\n"
       <<"  \"name\": \"value\",\n"
       <<"  \"key\": \"abc\", \n"
       <<" }";

now becomes

osjson << "{\n" <<"  \"name\": \"value\",\n <<"  \"key\": \"abc\",\n  << "}";

While i understand its correct for column width its not as nicer.

These rules about breaking between << were part of the original author rules for now to best try and format c++ and I sort of feel we should at least honour it via an option.

I also feel that this will create a large amount of complaints about us changing defaults.

[mydeveloperday]

see #88483

[owenca]

I wish we'd made this removal an option rather than just removing it, what we are seeing is reasonably formatted json or xml being streamed out is now poorly written

osjson << "{\n"
       <<"  \"name\": \"value\",\n"
       <<"  \"key\": \"abc\", \n"
       <<" }";

now becomes

osjson << "{\n" <<"  \"name\": \"value\",\n <<"  \"key\": \"abc\",\n  << "}";

What version was used? I've just tried clang-format 18.1.3, and it's totally fine:

$ cat lessless.cpp
osjson << "{\n"
       << "  \"name\": \"value\",\n"
       << "  \"key\": \"abc\", \n"
       << " }";
$ clang-format -version
clang-format version 18.1.3
$ clang-format lessless.cpp | diff lessless.cpp -
$