mingw: help debugging by optionally executing bash with strace

MSYS2's strace facility is very useful for debugging... With this patch,
the bash will be executed through strace if the environment variable
GIT_STRACE_COMMANDS is set, which comes in real handy when investigating
issues in the test suite.

Also support passing a path to a log file via GIT_STRACE_COMMANDS to
force Git to call strace.exe with the `-o <path>` argument, i.e. to log
into a file rather than print the log directly.

That comes in handy when the output would otherwise misinterpreted by a
calling process as part of Git's output.

Note: the values "1", "yes" or "true" are *not* specifying paths, but
tell Git to let strace.exe log directly to the console.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/compat/mingw.c b/compat/mingw.c
index f2c94f9d0849c7fd19890e17df57adffa4ad6c83..178a70df61fd2417de7fc0aeb4b8019f27b9536f 100644 (file)
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -1488,6 +1488,7 @@ static pid_t mingw_spawnve_fd(const char *cmd, const char **argv, char **deltaen
        const char *(*quote_arg)(const char *arg) =
                is_msys2_sh(cmd ? cmd : *argv) ?
                quote_arg_msys2 : quote_arg_msvc;
+       const char *strace_env;
 
        /* Make sure to override previous errors, if any */
        errno = 0;
@@ -1571,6 +1572,31 @@ static pid_t mingw_spawnve_fd(const char *cmd, const char **argv, char **deltaen
                        free(quoted);
        }
 
+       strace_env = getenv("GIT_STRACE_COMMANDS");
+       if (strace_env) {
+               char *p = path_lookup("strace.exe", 1);
+               if (!p)
+                       return error("strace not found!");
+               if (xutftowcs_path(wcmd, p) < 0) {
+                       free(p);
+                       return -1;
+               }
+               free(p);
+               if (!strcmp("1", strace_env) ||
+                   !strcasecmp("yes", strace_env) ||
+                   !strcasecmp("true", strace_env))
+                       strbuf_insert(&args, 0, "strace ", 7);
+               else {
+                       const char *quoted = quote_arg(strace_env);
+                       struct strbuf buf = STRBUF_INIT;
+                       strbuf_addf(&buf, "strace -o %s ", quoted);
+                       if (quoted != strace_env)
+                               free((char *)quoted);
+                       strbuf_insert(&args, 0, buf.buf, buf.len);
+                       strbuf_release(&buf);
+               }
+       }
+
        ALLOC_ARRAY(wargs, st_add(st_mult(2, args.len), 1));
        xutftowcs(wargs, args.buf, 2 * args.len + 1);
        strbuf_release(&args);