Re: [PATCH v2] unit-tests: do show relative file paths on non-Windows, too

>>
>> We know which separator we're expecting so we could replace  the last
>> two comparisons with
>>
>> 		prefix[prefix_len -1] != needle[1]
>>
>> but as I say I'm not sure that is worth re-rolling for
> 
> There is a larger clean-up opportunity to drop the need for making a
> copy, which probably is worth doing, so I folded the above into this
> version.

> ------- >8 ------------- >8 ------------- >8 ------------- >8 -------
> 
> There are compilers other than Visual C that want to show absolute
> paths.  Generalize the helper introduced by a2c5e294 (unit-tests: do
> show relative file paths, 2023-09-25) so that it can also work with
> a path that uses slash as the directory separator, and becomes
> almost no-op once one-time preparation finds out that we are using a
> compiler that already gives relative paths.  Incidentally, this also
> should do the right thing on Windows with a compiler that shows
> relative paths but with backslash as the directory separator (if
> such a thing exists and is used to build git).
> 
> Reported-by: Randall S. Becker <rsbecker@nexbridge.com>
> Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
> Signed-off-by: Junio C Hamano <gitster@pobox.com>
> ---
> 
>    * I found that the diff relative to the result of applying v1 was
>      easier to follow than the range-diff, so here it is.
> 
>    diff --git c/t/unit-tests/test-lib.c w/t/unit-tests/test-lib.c
>    index 83c9eb8c59..66d6980ffb 100644
>    --- c/t/unit-tests/test-lib.c
>    +++ w/t/unit-tests/test-lib.c
>    @@ -64,34 +64,33 @@ static const char *make_relative(const char *location)
>     		 * prefix_len == 0 if the compiler gives paths relative
>     		 * to the root of the working tree.  Otherwise, we want
>     		 * to see that we did find the needle[] at a directory
>    -		 * boundary.
>    +		 * boundary.  Again we rely on that needle[] begins with
>    +		 * "t" followed by the directory separator.
>     		 */
>     		if (fspathcmp(needle, prefix + prefix_len) ||
>    -		    (prefix_len &&
>    -		     prefix[prefix_len - 1] != '/' &&
>    -		     prefix[prefix_len - 1] != '\\'))
>    +		    (prefix_len && prefix[prefix_len - 1] != needle[1]))
>     			die("unexpected suffix of '%s'", prefix);
>    -
>     	}
>     
>     	/*
>    -	 * If our compiler gives relative paths and we do not need
>    -	 * to munge directory separator, we can return location as-is.
>    +	 * Does it not start with the expected prefix?
>    +	 * Return it as-is without making it worse.
>     	 */
>    -	if (!prefix_len && !need_bs_to_fs)
>    +	if (prefix_len && fspathncmp(location, prefix, prefix_len))
>     		return location;
>     
>    -	/* Does it not start with the expected prefix? */
>    -	if (fspathncmp(location, prefix, prefix_len))
>    -		return location;
>    +	/*
>    +	 * If we do not need to munge directory separator, we can return
>    +	 * the substring at the tail of the location.
>    +	 */
>    +	if (!need_bs_to_fs)
>    +		return location + prefix_len;
>     
>    -	strlcpy(buf, location + prefix_len, sizeof(buf));
>     	/* convert backslashes to forward slashes */
>    -	if (need_bs_to_fs) {
>    -		for (p = buf; *p; p++)
>    -			if (*p == '\\')
>    -				*p = '/';
>    -	}
>    +	strlcpy(buf, location + prefix_len, sizeof(buf));
>    +	for (p = buf; *p; p++)
>    +		if (*p == '\\')
>    +			*p = '/';
>     	return buf;
>     }
>     
> 
>   t/unit-tests/test-lib.c | 61 +++++++++++++++++++++++++++++++----------
>   1 file changed, 47 insertions(+), 14 deletions(-)
> 
> diff --git a/t/unit-tests/test-lib.c b/t/unit-tests/test-lib.c
> index 7bf9dfdb95..66d6980ffb 100644
> --- a/t/unit-tests/test-lib.c
> +++ b/t/unit-tests/test-lib.c
> @@ -21,12 +21,11 @@ static struct {
>   	.result = RESULT_NONE,
>   };
>   
> -#ifndef _MSC_VER
> -#define make_relative(location) location
> -#else
>   /*
>    * Visual C interpolates the absolute Windows path for `__FILE__`,
>    * but we want to see relative paths, as verified by t0080.
> + * There are other compilers that do the same, and are not for
> + * Windows.
>    */
>   #include "dir.h"
>   
> @@ -34,32 +33,66 @@ static const char *make_relative(const char *location)
>   {
>   	static char prefix[] = __FILE__, buf[PATH_MAX], *p;
>   	static size_t prefix_len;
> +	static int need_bs_to_fs = -1;
>   
> -	if (!prefix_len) {
> +	/* one-time preparation */
> +	if (need_bs_to_fs < 0) {
>   		size_t len = strlen(prefix);
> -		const char *needle = "\\t\\unit-tests\\test-lib.c";
> +		char needle[] = "t\\unit-tests\\test-lib.c";
>   		size_t needle_len = strlen(needle);
>   
> -		if (len < needle_len || strcmp(needle, prefix + len - needle_len))
> -			die("unexpected suffix of '%s'", prefix);
> +		if (len < needle_len)
> +			die("unexpected prefix '%s'", prefix);
> +
> +		/*
> +		 * The path could be relative (t/unit-tests/test-lib.c)
> +		 * or full (/home/user/git/t/unit-tests/test-lib.c).
> +		 * Check the slash between "t" and "unit-tests".
> +		 */
> +		prefix_len = len - needle_len;
> +		if (prefix[prefix_len + 1] == '/') {
> +			/* Oh, we're not Windows */
> +			for (size_t i = 0; i < needle_len; i++)
> +				if (needle[i] == '\\')
> +					needle[i] = '/';
> +			need_bs_to_fs = 0;
> +		} else {
> +			need_bs_to_fs = 1;
> +		}
>   
> -		/* let it end in a directory separator */
> -		prefix_len = len - needle_len + 1;
> +		/*
> +		 * prefix_len == 0 if the compiler gives paths relative
> +		 * to the root of the working tree.  Otherwise, we want
> +		 * to see that we did find the needle[] at a directory
> +		 * boundary.  Again we rely on that needle[] begins with
> +		 * "t" followed by the directory separator.
> +		 */
> +		if (fspathcmp(needle, prefix + prefix_len) ||
> +		    (prefix_len && prefix[prefix_len - 1] != needle[1]))
> +			die("unexpected suffix of '%s'", prefix);
>   	}
>   
> -	/* Does it not start with the expected prefix? */
> -	if (fspathncmp(location, prefix, prefix_len))
> +	/*
> +	 * Does it not start with the expected prefix?
> +	 * Return it as-is without making it worse.
> +	 */
> +	if (prefix_len && fspathncmp(location, prefix, prefix_len))
>   		return location;
>   
> -	strlcpy(buf, location + prefix_len, sizeof(buf));
> +	/*
> +	 * If we do not need to munge directory separator, we can return
> +	 * the substring at the tail of the location.
> +	 */
> +	if (!need_bs_to_fs)
> +		return location + prefix_len;
> +
>   	/* convert backslashes to forward slashes */
> +	strlcpy(buf, location + prefix_len, sizeof(buf));
>   	for (p = buf; *p; p++)
>   		if (*p == '\\')
>   			*p = '/';
> -
>   	return buf;
>   }
> -#endif
>   
>   static void msg_with_prefix(const char *prefix, const char *format, va_list ap)
>   {