C99: remove hardcoded-out !HAVE_VARIADIC_MACROS code

Remove the "else" branches of the HAVE_VARIADIC_MACROS macro, which
have been unconditionally omitted since 765dc168882 (git-compat-util:
always enable variadic macros, 2021-01-28).

Since were always omitted, anyone trying to use a compiler without
variadic macro support to compile a git since version
git v2.31.0 or later would have had a compilation error. 10 months
across a few releases since then should have been enough time for
anyone who cared to run into that and report the issue.

In addition to that, for anyone unsetting HAVE_VARIADIC_MACROS we've
been emitting extremely verbose warnings since at least
ee4512ed481 (trace2: create new combined trace facility,
2019-02-22). That's because there is no such thing as a
"region_enter_printf" or "region_leave_printf" format, so at least
under GCC and Clang everything that includes trace.h (almost every
file) emits a couple of warnings about that.

There's a large benefit to being able to have a hard dependency rely
on variadic macros, the code surrounding usage.c is hard to maintain
if we need to write two implementations of everything, and by relying
on "__FILE__" and "__LINE__" along with "__VA_ARGS__" we can in the
future make error(), die() etc. log where they were called from. We've
also recently merged d67fc4bf0ba (Merge branch 'bc/require-c99',
2021-12-10) which further cements our hard dependency on C99.

So let's delete the fallback code, and update our CodingGuidelines to
note that we depend on this. The added bullet-point starts with
lower-case for consistency with other bullet-points in that section.

The diff in "trace.h" is relatively hard to read, since we need to
retain the existing API docs, which were comments on the code used if
HAVE_VARIADIC_MACROS was not defined.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 58 insertions, 70 deletions

diff --git a/trace.h b/trace.h
index e259840..4e771f8 100644
--- a/trace.h
+++ b/trace.h
@@ -126,71 +126,6 @@ void trace_command_performance(const char **argv);
 void trace_verbatim(struct trace_key *key, const void *buf, unsigned len);
 uint64_t trace_performance_enter(void);
 
-#ifndef HAVE_VARIADIC_MACROS
-
-/**
- * Prints a formatted message, similar to printf.
- */
-__attribute__((format (printf, 1, 2)))
-void trace_printf(const char *format, ...);
-
-__attribute__((format (printf, 2, 3)))
-void trace_printf_key(struct trace_key *key, const char *format, ...);
-
-/**
- * Prints a formatted message, followed by a quoted list of arguments.
- */
-__attribute__((format (printf, 2, 3)))
-void trace_argv_printf(const char **argv, const char *format, ...);
-
-/**
- * Prints the strbuf, without additional formatting (i.e. doesn't
- * choke on `%` or even `\0`).
- */
-void trace_strbuf(struct trace_key *key, const struct strbuf *data);
-
-/**
- * Prints elapsed time (in nanoseconds) if GIT_TRACE_PERFORMANCE is enabled.
- *
- * Example:
- * ------------
- * uint64_t t = 0;
- * for (;;) {
- * 	// ignore
- * t -= getnanotime();
- * // code section to measure
- * t += getnanotime();
- * // ignore
- * }
- * trace_performance(t, "frotz");
- * ------------
- */
-__attribute__((format (printf, 2, 3)))
-void trace_performance(uint64_t nanos, const char *format, ...);
-
-/**
- * Prints elapsed time since 'start' if GIT_TRACE_PERFORMANCE is enabled.
- *
- * Example:
- * ------------
- * uint64_t start = getnanotime();
- * // code section to measure
- * trace_performance_since(start, "foobar");
- * ------------
- */
-__attribute__((format (printf, 2, 3)))
-void trace_performance_since(uint64_t start, const char *format, ...);
-
-__attribute__((format (printf, 1, 2)))
-void trace_performance_leave(const char *format, ...);
-
-#else
-
-/*
- * Macros to add file:line - see above for C-style declarations of how these
- * should be used.
- */
-
 /*
  * TRACE_CONTEXT may be set to __FUNCTION__ if the compiler supports it. The
  * default is __FILE__, as it is consistent with assert(), and static function
@@ -204,7 +139,10 @@ void trace_performance_leave(const char *format, ...);
 # define TRACE_CONTEXT __FILE__
 #endif
 
-/*
+/**
+ * Macros to add the file:line of the calling code, instead of that of
+ * the trace function itself.
+ *
  * Note: with C99 variadic macros, __VA_ARGS__ must include the last fixed
  * parameter ('format' in this case). Otherwise, a call without variable
  * arguments will have a surplus ','. E.g.:
@@ -220,6 +158,16 @@ void trace_performance_leave(const char *format, ...);
  * comma, but this is non-standard.
  */
 
+/**
+ * trace_printf(), accepts "const char *format, ...".
+ *
+ * Prints a formatted message, similar to printf.
+ */
+#define trace_printf(...) trace_printf_key(&trace_default_key, __VA_ARGS__)
+
+/**
+ * trace_printf_key(), accepts "struct trace_key *key, const char *format, ...".
+ */
 #define trace_printf_key(key, ...)					    \
 	do {								    \
 		if (trace_pass_fl(key))					    \
@@ -227,8 +175,11 @@ void trace_performance_leave(const char *format, ...);
 					    __VA_ARGS__);		    \
 	} while (0)
 
-#define trace_printf(...) trace_printf_key(&trace_default_key, __VA_ARGS__)
-
+/**
+ * trace_argv_printf(), accepts "struct trace_key *key, const char *format, ...)".
+ *
+ * Prints a formatted message, followed by a quoted list of arguments.
+ */
 #define trace_argv_printf(argv, ...)					    \
 	do {								    \
 		if (trace_pass_fl(&trace_default_key))			    \
@@ -236,12 +187,36 @@ void trace_performance_leave(const char *format, ...);
 					    argv, __VA_ARGS__);		    \
 	} while (0)
 
+/**
+ * trace_strbuf(), accepts "struct trace_key *key, const struct strbuf *data".
+ *
+ * Prints the strbuf, without additional formatting (i.e. doesn't
+ * choke on `%` or even `\0`).
+ */
 #define trace_strbuf(key, data)						    \
 	do {								    \
 		if (trace_pass_fl(key))					    \
 			trace_strbuf_fl(TRACE_CONTEXT, __LINE__, key, data);\
 	} while (0)
 
+/**
+ * trace_performance(), accepts "uint64_t nanos, const char *format, ...".
+ *
+ * Prints elapsed time (in nanoseconds) if GIT_TRACE_PERFORMANCE is enabled.
+ *
+ * Example:
+ * ------------
+ * uint64_t t = 0;
+ * for (;;) {
+ * 	// ignore
+ * t -= getnanotime();
+ * // code section to measure
+ * t += getnanotime();
+ * // ignore
+ * }
+ * trace_performance(t, "frotz");
+ * ------------
+ */
 #define trace_performance(nanos, ...)					    \
 	do {								    \
 		if (trace_pass_fl(&trace_perf_key))			    \
@@ -249,6 +224,18 @@ void trace_performance_leave(const char *format, ...);
 					     __VA_ARGS__);		    \
 	} while (0)
 
+/**
+ * trace_performance_since(), accepts "uint64_t start, const char *format, ...".
+ *
+ * Prints elapsed time since 'start' if GIT_TRACE_PERFORMANCE is enabled.
+ *
+ * Example:
+ * ------------
+ * uint64_t start = getnanotime();
+ * // code section to measure
+ * trace_performance_since(start, "foobar");
+ * ------------
+ */
 #define trace_performance_since(start, ...)				    \
 	do {								    \
 		if (trace_pass_fl(&trace_perf_key))			    \
@@ -257,6 +244,9 @@ void trace_performance_leave(const char *format, ...);
 					     __VA_ARGS__);		    \
 	} while (0)
 
+/**
+ * trace_performance_leave(), accepts "const char *format, ...".
+ */
 #define trace_performance_leave(...)					    \
 	do {								    \
 		if (trace_pass_fl(&trace_perf_key))			    \
@@ -285,6 +275,4 @@ static inline int trace_pass_fl(struct trace_key *key)
 	return key->fd || !key->initialized;
 }
 
-#endif /* HAVE_VARIADIC_MACROS */
-
 #endif /* TRACE_H */