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

[Nathan Sidwell <nathan@acm.org>]

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?

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)
>>

-- 
Nathan Sidwell