Clang could warn about trailing spaces in `#include` filenames

[zmodem]

Consider:

#include "foo.h " // Note: trailing space.

Assuming foo.h exists, the code above will compile on Windows whose filesystem API generally ignores leading and trailing space in filenames. However it will not compile on stricter systems such as Linux.

Maybe Clang should warn? It's niche, but also seems easy to do.

(Yes, we hit this in real code, https://chromium-review.googlesource.com/c/chromium/src/+/5641197)

[MitalAshok]

This also breaks -Wnonportable-include-path:

#include <array>
#include <array >
#include <Array >
#include <Array>

> clang-cl clang-cl test.cpp -fsyntax-only
test.cpp(4,10): warning: non-portable path to file '<array>'; specified path differs in case from file name on disk
      [-Wnonportable-include-path]
    4 | #include <Array>
      |          ^~~~~~~
      |          <array>
1 warning generated.

We should probably extend -Wnonportable-include-path to consider trailing spaces.

Dots at the end are ignored in the same way on Windows too:

// All of these include the same file
#include <Array >
#include <Array.>
#include <Array              >
#include <Array..............>
#include <Array.             >
#include <Array    . . ...  .>

Since these trailing spaces/dots are always removed when you specify a filename (except when prefixed by \\?\), we could issue the warning before even opening the file https://learn.microsoft.com/en-gb/windows/win32/fileio/naming-a-file#naming-conventions (There's probably a more authoritative source on how the file name is transformed, this one only says "Do not end a file or directory name with a space or a period.")

[zmodem]

+1 extending -Wnonportable-include-path for this sounds good!

[llvmbot]

Hi!

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[llvmbot]

@llvm/issue-subscribers-good-first-issue

Author: Hans (zmodem)

Consider: ``` #include "foo.h " // Note: trailing space. ``` Assuming `foo.h` exists, the code above will compile on Windows whose filesystem API generally ignores leading and trailing space in filenames. However it will not compile on stricter systems such as Linux. Maybe Clang should warn? It's niche, but also seems easy to do. (Yes, we hit this in real code, https://chromium-review.googlesource.com/c/chromium/src/+/5641197)

[akshaykumars614]

Let me understand the issue. You are saying

include"foo.h " should throw a warning, but it is not?

I am I right? I am new here. Trying to understand things @zmodem

[jerryyiransun]

I would like to work on this issue, can I get assigned please? @shafik