Transition to C99

[JohnoKing]

This commit is a compilation of many old patches of mine. It removes obsolete code and enforces C99 as a build requirement.

Changes:

• Remove many unused tests and useless feature tests. (This was a bit more involved for <sys/types.h>, which had annoying special casing.) This included the "check for global headers" in the iffe script.
• Assume fchmod is present and use it instead of chmod in shcomp for very slightly better performance.
• dotpaths_lib(): Use fstat rather than stat for the PWD for better performance.
• Scrap pre-C99 fallbacks for iswblank(3).
• Replaced usage of the obsolescent timeofday() macro with the more portable tvgettime() function in libast, which itself uses the modern clock_gettime internally when it's available.
• Replaced usage of strcopy with either strcpy or stpcpy in cases where no buffer overlap occurs. There are perhaps more places where replacement is possible (ksh93v- and ksh2020 do this far more liberally), but I'm trying to be conservative with these changes to avoid accidentally introducing bugs.
• Replaced an instance of strncopy with strlcpy in keytrap() because the buffers don't overlap.
  • Also replaced some instances of strncpy with strlcpy (vide ksh2020 commit f63ebd0 and associated issue Replace uses of strncpy() with strlcpy() att/ast#266).
• Add pertinent documentation as it relates to str*copy's usage with overlapping buffers.
• Backported a modified version of ksh93v-'s stpcpy fallback.
• Introduced usage of C99 restrict, primarily for standards compliance in compatibility functions (though some regular functions like sfopen() will also use restrict now).
• Assume C99 __func__ is available and drop now unnecessary C90 feature tests.
• Added a few casts to fix some compiler warnings.
• Remove basic iffe probes for various C99 multibyte functions (excluding those that still need tests due to platform-specific bugs). Also removed other unnecessary probes for C99 and POSIX functionality.
• Remove unnecessary mktime.c, wc.c and wordexp.c compat files (the operating system should provide these functions).
• Switched to using C99-style struct init throughout the codebase.
• Removed usage of bzero, bcopy, memclear and memzero in favor of standard memset and memcpy.
• Minor bugfix: avoid passing overlapping buffers to getaddrinfo in io.c because that violates the POSIX standard.
• make.probe: Automatically use the latest C standard available (i.e. C23) because GCC/Clang may use something older by default whilst having support for newer standards.

I have additional changes for using C99-style for loops and bools, but those have been excluded because this patch is big enough as it is. I also encountered crashing bugs when I attempted to remove widespread usage of the struct hack, so the struct hack was only removed if it was already disabled by a preexisting __STDC_VERSION__ check.

Progresses #777 (this commit doesn't include or fix the removed _c99_in_the_wild code).

[McDutchie]

I have additional changes for using C99-style for loops and bools, but those have been excluded because this patch is big enough as it is.

I would also like to think about/discuss this some more before committing to these, because so far I'm failing to see an actual advantage to either of these.

I quite like the C90 norm that all variables are declared at the beginning of each braces block that they're scoped to; it's good for clarity, IMHO.

As for bools, are they really any more than syntactic sugar? I could be missing something, e.g., do they improve performance? If not, I don't feel the need for them.

[McDutchie]

Alright, I think we're going to a need C99 flexible struct member to fix the alignment issue in #964 without more hackery. So, it's time for this.

[McDutchie]

Unfortunately, the PR doesn't build on macOS.

# src/lib/libast/Mamfile: 2305-2311: make strntold.o
+ compile /usr/local/src/ksh93/ksh/src/lib/libast/string/strntold.c -Iport -I/usr/local/src/ksh93/ksh/src/lib/libast/port -Isfio -I/usr/local/src/ksh93/ksh/src/lib/libast/sfio
+ s=/usr/local/src/ksh93/ksh/src/lib/libast/string/strntold.c
+ shift
+ cc -D_BLD_ast '-std=gnu23' -O0 -g -Wall -funsigned-char -fno-strict-aliasing -I. -I/usr/local/src/ksh93/ksh/src/lib/libast -Icomp -I/usr/local/src/ksh93/ksh/src/lib/libast/comp -Iport -I/usr/local/src/ksh93/ksh/src/lib/libast/port -Isfio -I/usr/local/src/ksh93/ksh/src/lib/libast/sfio -Iinclude -I/usr/local/src/ksh93/ksh/src/lib/libast/include -Istd -I/usr/local/src/ksh93/ksh/src/lib/libast/std -c /usr/local/src/ksh93/ksh/src/lib/libast/string/strntold.c
In file included from /usr/local/src/ksh93/ksh/src/lib/libast/string/strntold.c:29:
/usr/local/src/ksh93/ksh/src/lib/libast/sfio/sfstrtof.h:160:1: error: conflicting types for 'strntold'
  160 | S2F_function(const char* str, size_t size, char** end)
      | ^
/usr/local/src/ksh93/ksh/src/lib/libast/string/strntold.c:25:22: note: expanded from macro 'S2F_function'
   25 | #define S2F_function    strntold
      |                         ^
/usr/local/src/ksh93/ksh/src/lib/libast/include/ast.h:378:20: note: previous declaration is here
  378 | extern long double      strntold(const char*, size_t, char**);
      |                         ^
1 error generated.
mamake [lib/libast]: *** exit code 1 making strntold.o
mamake: *** exit code 1 making lib/libast
mamake: *** exit code 1 making all
package: make failed at Sat Apr  4 22:13:28 BST 2026 in /usr/local/src/ksh93/ksh/arch/darwin.arm64-64,d

[JohnoKing]

I quite like the C90 norm that all variables are declared at the beginning of each braces block that they're scoped to; it's good for clarity, IMHO.

As for bools, are they really any more than syntactic sugar? I could be missing something, e.g., do they improve performance? If not, I don't feel the need for them.

Local variables in for loops via for(int i = 0; etc) and bools are ultimately secondary, being primarily useful for readability (the former helps with large functions that repeatedly use an i variable, since it can be unclear whether the value is actually used outside of the loop if the function is exceedingly long).
I primarily want to utilize C99's restrict, struct initializers and (for a later PR) variadic macros.

Unfortunately, the PR doesn't build on macOS.

I don't have anything running macOS, but perhaps that's caused by sfstrtof.h using double instead of long double. Test patch:

--- a/src/lib/libast/sfio/sfstrtof.h
+++ b/src/lib/libast/sfio/sfstrtof.h
@@ -59,11 +59,6 @@
 #endif
 #endif
 
-#if S2F_type == 2 && _ast_fltmax_double
-#undef	S2F_type
-#define S2F_type	1
-#endif
-
 #if S2F_type == 0
 #define S2F_number	float
 #define S2F_ldexp	ldexp