Re: [PATCH] c++: Allow module name to be a single letter on Windows

[Torbjorn SVENSSON <torbjorn.svensson@foss.st.com>]

Hi Nathan,

On 2022-11-08 00:03, Nathan Sidwell wrote:
> On 11/3/22 11:06, Torbjorn SVENSSON wrote:
>>
>>
>> On 2022-11-03 15:17, Nathan Sidwell wrote:
>>> On 10/28/22 05:15, Torbjörn SVENSSON wrote:
>>>> On Windows, the ':' character is special and when the module name is
>>>> a single character, like 'A', then the flatname would be (for
>>>> example) 'A:Foo'. On Windows, 'A:Foo' is treated as an absolute
>>>> path by the module loader and is likely not found.
>>>>
>>>> Without this patch, the test case pr98944_c.C fails with:
>>>>
>>>> In module imported at 
>>>> /src/gcc/testsuite/g++.dg/modules/pr98944_b.C:7:1,
>>>> of module A:Foo, imported at 
>>>> /src/gcc/testsuite/g++.dg/modules/pr98944_c.C:7:
>>>> A:Internals: error: header module expected, module 'A:Internals' found
>>>> A:Internals: error: failed to read compiled module: Bad file data
>>>> A:Internals: note: compiled module file is 'gcm.cache/A-Internals.gcm'
>>>> In module imported at 
>>>> /src/gcc/testsuite/g++.dg/modules/pr98944_c.C:7:8:
>>>> A:Foo: error: failed to read compiled module: Bad import dependency
>>>> A:Foo: note: compiled module file is 'gcm.cache/A-Foo.gcm'
>>>> A:Foo: fatal error: returning to the gate for a mechanical issue
>>>> compilation terminated.
>>>>
>>>> include/ChangeLog:
>>>>
>>>>     * filenames.h: Added IS_REAL_ABSOLUTE_PATH macro to check if
>>>>     path is absolute and not semi-absolute on Windows.
>>>
>>> Hm, this is unfortunate.  The current IS_ABSOLUTE_PATH, is really 
>>> 'not relative to cwd', and even then that's untrue if the drive 
>>> letter there is the drive letter of cwd, right?
>>>
>>> It's awkward to have a new macro for just this purpose and the new 
>>> name isn't very indicative of the difference to the current 
>>> IS_ABSOLUTE_PATH.
>>>
>>> Would it be better to not deal with drive letters here?  How 
>>> prevalent are they these days in windows?  Would something like
>>>
>>>     if (IS_DIR_SEPARATOR (ptr[ptr[0] == '.'])
>>>
>>> suffice?
>>
>> I don't think you can ignore the drive letter part... see below.
>>
>>
>> #include <stdio.h>
>> #include "include/filenames.h"
>> #define TF(x) ((x) ? "true" : "false")
>> int main(int argc, char *argv[]) {
>>    const char *test[] = {
>>        /* absolute */      "c:\\foo", "c:/foo", "/foo", "\\foo",
>>        /* semi-absolute */ "c:foo",
>>        /* relative */      "foo", "./foo", ".\\foo",
>>    };
>>    for (int i = 0; i < sizeof(test) / sizeof(test[0]); i++) {
>>      const char *ptr = test[i];
>>      printf("\nptr: %s\n", ptr);
>>      printf("  IS_DOS_ABSOLUTE_PATH: %s\n",
>>             TF(IS_DOS_ABSOLUTE_PATH(ptr)));
>>      printf("  IS_DOS_REAL_ABSOLUTE_PATH: %s\n",
>>             TF(IS_DOS_REAL_ABSOLUTE_PATH(ptr)));
>>      printf("  IS_DIR_SEPARATOR: %s\n",
>>             TF(IS_DIR_SEPARATOR(ptr[ptr[0] == '.'])));
>>    }
>>    return 0;
>> }
>>
>>
>> The output is:
>>
>> ptr: c:\foo
>>    IS_DOS_ABSOLUTE_PATH: true
>>    IS_DOS_REAL_ABSOLUTE_PATH: true
>>    IS_DIR_SEPARATOR: false
>>
>> ptr: c:/foo
>>    IS_DOS_ABSOLUTE_PATH: true
>>    IS_DOS_REAL_ABSOLUTE_PATH: true
>>    IS_DIR_SEPARATOR: false
>>
>> ptr: /foo
>>    IS_DOS_ABSOLUTE_PATH: true
>>    IS_DOS_REAL_ABSOLUTE_PATH: true
>>    IS_DIR_SEPARATOR: true
>>
>> ptr: \foo
>>    IS_DOS_ABSOLUTE_PATH: true
>>    IS_DOS_REAL_ABSOLUTE_PATH: true
>>    IS_DIR_SEPARATOR: false
>>
>> ptr: c:foo
>>    IS_DOS_ABSOLUTE_PATH: true
>>    IS_DOS_REAL_ABSOLUTE_PATH: false
>>    IS_DIR_SEPARATOR: false
>>
>> ptr: foo
>>    IS_DOS_ABSOLUTE_PATH: false
>>    IS_DOS_REAL_ABSOLUTE_PATH: false
>>    IS_DIR_SEPARATOR: false
>>
>> ptr: ./foo
>>    IS_DOS_ABSOLUTE_PATH: false
>>    IS_DOS_REAL_ABSOLUTE_PATH: false
>>    IS_DIR_SEPARATOR: true
>>
>> ptr: .\foo
>>    IS_DOS_ABSOLUTE_PATH: false
>>    IS_DOS_REAL_ABSOLUTE_PATH: false
>>    IS_DIR_SEPARATOR: false
>>
>>
>>>
>>> or, failing that perhaps put some explicit WINDOWS-specific #ifdef'd 
>>> code there?  It's a real corner case.
>>
>> Would you rather have something like this in module.cc?
>>
>> if (ptr[0] == '.')
>>    {
>>      if IS_DIR_SEPARATOR (ptr[1]))
>>        return get_module (build_string (strlen (ptr), ptr));
>>    }
>> else
>>    {
>> #if HAVE_DOS_BASED_FILE_SYSTEM
>>      if (HAS_DRIVE_SPEC (ptr) && IS_DIR_SEPARATOR (ptr[2]))
>> #else
>>      if (IS_ABSOLUTE_PATH (ptr))
>> #endif
>>        return get_module (build_string (strlen (ptr), ptr));
>>    }
> 
> Yes, something like the above, but I think you're missing "/bob' in the 
> DOS_BASED case?  shouldn't that also be a pathname?
> 
> if (IS_DIR_SEPARATOR (ptr[ptr[0] == '.']) // ./FOO or /FOO
> #if HAVE_DOS_BASED_FILE_SYSTEM
>      // DOS-FS IS_ABSOLUTE_PATH thinks 'A:B' is absolute, but we need to 
> consider
>      // that as a module:partition.
>      || (HAS_DRIVE_SPEC (ptr) && IS_DIR_SEPARATOR (ptr[2])) // A:/FOO
> #endif
>      || false)
>     return ....
> 
> Does (something like) that work?

I tested it and your solution appears to work.
Are you okay with me pushing that solution or do you want me to send a 
v2 with it first?

Kind regards,
Torbjörn

> 
> nathan
> 
>>
>>
>> Let me know what you prefer.
>>
>> Kind regards,
>> Torbjörn
>>
>>>
>>> nathan
>>>
>>>>
>>>> gcc/cp/ChangeLog:
>>>>
>>>>     * module.cc: Use IS_REAL_ABSOLUTE_PATH macro.
>>>>
>>>> Co-Authored-By: Yvan ROUX <yvan.roux@foss.st.com>
>>>> Signed-off-by: Torbjörn SVENSSON <torbjorn.svensson@foss.st.com>
>>>> ---
>>>>   gcc/cp/module.cc    | 2 +-
>>>>   include/filenames.h | 4 ++++
>>>>   2 files changed, 5 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
>>>> index 9957df510e6..84680e183b7 100644
>>>> --- a/gcc/cp/module.cc
>>>> +++ b/gcc/cp/module.cc
>>>> @@ -13958,7 +13958,7 @@ get_module (tree name, module_state *parent, 
>>>> bool partition)
>>>>   static module_state *
>>>>   get_module (const char *ptr)
>>>>   {
>>>> -  if (ptr[0] == '.' ? IS_DIR_SEPARATOR (ptr[1]) : IS_ABSOLUTE_PATH 
>>>> (ptr))
>>>> +  if (ptr[0] == '.' ? IS_DIR_SEPARATOR (ptr[1]) : 
>>>> IS_REAL_ABSOLUTE_PATH (ptr))
>>>>       /* A header name.  */
>>>>       return get_module (build_string (strlen (ptr), ptr));
>>>> diff --git a/include/filenames.h b/include/filenames.h
>>>> index 6c72c422edd..d04fccfed64 100644
>>>> --- a/include/filenames.h
>>>> +++ b/include/filenames.h
>>>> @@ -43,6 +43,7 @@ extern "C" {
>>>>   #  define HAS_DRIVE_SPEC(f) HAS_DOS_DRIVE_SPEC (f)
>>>>   #  define IS_DIR_SEPARATOR(c) IS_DOS_DIR_SEPARATOR (c)
>>>>   #  define IS_ABSOLUTE_PATH(f) IS_DOS_ABSOLUTE_PATH (f)
>>>> +#  define IS_REAL_ABSOLUTE_PATH(f) IS_DOS_REAL_ABSOLUTE_PATH (f)
>>>>   #else /* not DOSish */
>>>>   #  if defined(__APPLE__)
>>>>   #    ifndef HAVE_CASE_INSENSITIVE_FILE_SYSTEM
>>>> @@ -52,6 +53,7 @@ extern "C" {
>>>>   #  define HAS_DRIVE_SPEC(f) (0)
>>>>   #  define IS_DIR_SEPARATOR(c) IS_UNIX_DIR_SEPARATOR (c)
>>>>   #  define IS_ABSOLUTE_PATH(f) IS_UNIX_ABSOLUTE_PATH (f)
>>>> +#  define IS_REAL_ABSOLUTE_PATH(f) IS_ABSOLUTE_PATH (f)
>>>>   #endif
>>>>   #define IS_DIR_SEPARATOR_1(dos_based, c)                \
>>>> @@ -67,6 +69,8 @@ extern "C" {
>>>>   #define IS_DOS_DIR_SEPARATOR(c) IS_DIR_SEPARATOR_1 (1, c)
>>>>   #define IS_DOS_ABSOLUTE_PATH(f) IS_ABSOLUTE_PATH_1 (1, f)
>>>> +#define IS_DOS_REAL_ABSOLUTE_PATH(f) \
>>>> +  ((f)[0] && (f)[1] == ':' && ((f)[2] == '/' || (f)[2] == '\\'))
>>>>   #define HAS_DOS_DRIVE_SPEC(f) HAS_DRIVE_SPEC_1 (1, f)
>>>>   #define IS_UNIX_DIR_SEPARATOR(c) IS_DIR_SEPARATOR_1 (0, c)
>>>
>