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

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

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));
   }


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)
>