diff contrib/chg/chg.c @ 45551:4c8d9b53b1c7

chg: make is possible to call by default an hg binary located next to chg

When a single version of hg is in use and it's in the PATH, using chg
is just a matter of calling chg.

But when there are multiple installations of hg+chg around, and hg is
referred to with an absolute path, using chg is more annoying because
it requires both changing the invocation to hg to use chg, but also
setting CHGHG.

Currently, we set HGPATH when we build chg to remove the need to set
CHGHG in the previous paragraph. But that means chg now hardcodes its
installation path, which makes the installation not relocatable. Hence
this proposal to make chg find ./hg relative to itself (as opposed to
CHGHG=./hg which find hg relative to cwd).

This only works on linux as written, but since it's opt-in, it sounds
fine.

Tested by hand, as I'm not sure how else to test this.

Differential Revision: https://phab.mercurial-scm.org/D9006

--- a/contrib/chg/chg.c	Wed Sep 23 14:44:21 2020 +0200
+++ b/contrib/chg/chg.c	Thu Sep 03 11:07:47 2020 -0400
@@ -184,13 +184,46 @@
 		abortmsg("too long TMPDIR or CHGSOCKNAME (r = %d)", r);
 }
 
+/* If the current program is, say, /a/b/c/chg, returns /a/b/c/hg. */
+static char *getrelhgcmd(void)
+{
+	ssize_t n;
+	char *res, *slash;
+	int maxsize = 4096;
+	res = malloc(maxsize);
+	if (res == NULL)
+		goto cleanup;
+	n = readlink("/proc/self/exe", res, maxsize);
+	if (n < 0 || n >= maxsize)
+		goto cleanup;
+	res[n] = '\0';
+	slash = strrchr(res, '/');
+	if (slash == NULL)
+		goto cleanup;
+	/* 4 is strlen("/hg") + nul byte */
+	if (slash + 4 >= res + maxsize)
+		goto cleanup;
+	memcpy(slash, "/hg", 4);
+	return res;
+cleanup:
+	free(res);
+	return NULL;
+}
+
 static const char *gethgcmd(void)
 {
 	static const char *hgcmd = NULL;
+#ifdef HGPATHREL
+	int tryrelhgcmd = 1;
+#else
+	int tryrelhgcmd = 0;
+#endif
 	if (!hgcmd) {
 		hgcmd = getenv("CHGHG");
 		if (!hgcmd || hgcmd[0] == '\0')
 			hgcmd = getenv("HG");
+		if (tryrelhgcmd && (!hgcmd || hgcmd[0] == '\0'))
+			hgcmd = getrelhgcmd();
 		if (!hgcmd || hgcmd[0] == '\0')
 #ifdef HGPATH
 			hgcmd = (HGPATH);