[clang-format] Also look for .{ext}.clang-format file

[wanders]

Summary

E.g: When formatting foo.cpp it will look for .cpp.clang-format

This makes it easy to different formatting for .c/.h files and
.cpp/.hpp files within the same directories.

[wanders]

This depends on https://reviews.llvm.org/D68568

[MyDeveloperDay]

Thanks for the patch, I think I understand what you are trying to do, but I have a few questions.

Is the premise here that you need slightly different styles for .cpp than for .h? could you explain why?

whilst I can see there is value in having such fine control, could you explain a little what leads you to needing that? because it feels like you are almost saying a bug in clang-format prevents me from using a single file and I'd like to understand if that is the case?

clang/lib/Format/Format.cpp

2606

if Extension is a std::string use if (!Extension.empty())

[lebedev.ri]

I'm not seeing any merrit this brings over existing https://clang.llvm.org/docs/ClangFormatStyleOptions.html Language option.

[wanders]

The "Language" option can not distinguish between C and C++.

We have projects which contains both C and C++ code. Using different style (yes..) for C and C++. Our C++ headers are named hpp.

In our toplevel we have the following symlinks
.c.clang-format -> clang-format/c.clang-format
.h.clang-format -> clang-format/c.clang-format
.cpp.clang-format -> clang-format/cpp.clang-format
.hpp.clang-format -> clang-format/cpp.clang-format

Before this we had a horrible wrapper script that used cd into different directories depending on extension, and those directories had different .clang-format files, and then had to run clang-format from stdin.

An alternative implementation I did consider was to add some kind of path matching in the configuration file doing multiple yaml documents in the configuration file. So in my case it would be something like:

---
Language: Cpp
IndentWidth: 4
TabWidth: 4
MoreStuff...
---
PathMatch: [ *.cpp, *.hpp ]
SpaceBeforeParen: ControlStatements
---
PathMatch [ *.c, *.h ]
SpaceBeforeParen: Never
---

[MyDeveloperDay]

clang/lib/Format/Format.cpp

2603

Nit: almost every file has an extension should this be 3?

[lebedev.ri]

In D68569#1697248, @wanders wrote:

The "Language" option can not distinguish between C and C++.

We have projects which contains both C and C++ code. Using different style (yes..) for C and C++. Our C++ headers are named hpp.

That seems like a much smaller bug/feature to fix ?

[MyDeveloperDay]

Can we abandon this review now we have the style=file:<filename>?

[wanders]

In D68569#2019895, @MyDeveloperDay wrote:

Can we abandon this review now we have the style=file:<filename>?

Yes, lets abandon this.

clang/lib/Format/Format.cpp

2606

It is a StringRef (StringRef llvm::sys::path::extension(StringRef path)) but that also has empty(), thanks.

clang/docs/ClangFormat.rst

 
 When the desired code formatting style is different from the available options,
 the style can be customized using the ``-style="{key: value, ...}"`` option or
-by putting your style configuration in the ``.clang-format`` or ``_clang-format``
-file in your project's directory and using ``clang-format -style=file``.
+by putting your style configuration a file named ``.{ext}.clang-format`` (``{ext}``
+is the file name extension, e.g. ``.cpp.clang-format`` is the formatted file
+is named ``something.cpp``), ``.clang-format`` or ``_clang-format`` in your
+project's directory and using ``clang-format -style=file``.
 
 An easy way to create the ``.clang-format`` file is:
 

clang/lib/Format/Format.cpp

     return make_string_error(EC.message());
 
   llvm::SmallVector<std::string, 2> FilesToLookFor;
+
+  auto Extension(llvm::sys::path::extension(FileName));
+  if (Extension != "") {
+    FilesToLookFor.push_back((Extension + ".clang-format").str());
+  }
   FilesToLookFor.push_back(".clang-format");
   FilesToLookFor.push_back("_clang-format");