Fix showing current path again.

Avoid unnecessary heap allocations (though we added new ones in main())
if possible by using a PATH_MAX buffer.

Check for PWD matching current directory ourselves, which allows us to
save a stat syscall, by re-using the stat(".") result to compare to
stat("$HOME"). Improve how we check if HOME is actually part of pwd -
previous would get confused with "${HOME}char", which should not get the
prompt to display '~'.

Use strtok_r to scan characters now. Writing directly to p() makes more
sense than writing chars to a buffer, so remove that.

I'm somewhat unhappy with the rpwd and mrpwd solution, since while
coding I forgot to set one or the other a couple of times. It would be
nice if I could "unconst" the variable at some point, though I greatly
dislike that pattern.

ep.c

@@ -70,12 +70,18 @@ int main(int argc, char **argv)
 	if (chroot)
 		p("[chroot] ");
 
+	/* XXX: treat allocation failures as variables not existing in environment */
 	const char *home = getenv("HOME");
+	char *pwd = getenv("PWD");
+	#define cond_strdup(s) s = (s ? strdup(s) : s)
+	cond_strdup(home);
+	cond_strdup(pwd);
+	#undef cond_strdup
 
 	/* show we are on a different machine */
 	print_ssh();
 
-	print_pwd(home);
+	print_pwd(home, pwd);
 
 	/* git status */
 	void *git_info;

ep.h

@@ -24,7 +24,7 @@ void e(enum log_level_value, const char *, int);
 
 /* from path.c */
 extern const int fish_style_dir;
-void print_pwd(const char *);
+void print_pwd(const char *, char *);
 
 /* from git.c */
 void *git_thread(void *);

path.c

@@ -1,6 +1,8 @@
 #include <string.h>
 #include <stdlib.h>
 #include <unistd.h>
+#include <limits.h>
+#include <sys/stat.h>
 
 #include "ep.h"
 #include "info_strings.h"
@@ -8,41 +10,82 @@
 /* print current dir in fish style */
 const int fish_style_dir = 1;
 
-void print_pwd(const char *home)
+static inline int file_match(const struct stat *s1, const struct stat *s2)
 {
-	char *pwd = get_current_dir_name(), *rpwd = pwd;
+	return s1->st_dev == s2->st_dev && s1->st_ino == s2->st_ino;
+}
+
+void print_pwd(const char *home, char *envpwd)
+{
+	struct stat st_pwd, st_envpwd, st_home;
+	char pwd[PATH_MAX];
+	char *mrpwd = getcwd(pwd, sizeof pwd);
+	/* const alias to avoid accidentally modifying m(utable)rpwd.
+	 * remember to ALWAYS change both variables */
+	const char *rpwd = mrpwd;
 	if (!rpwd) {
-		/* get_current_dir_name failed */
+		/* getcwd failed */
 		p(unknowndir);
 	} else {
+		/* if envpwd exists and is valid (starts with '/' and matches current dir),
+		 * replace pwd with it */
+		if (envpwd && envpwd[0] == '/') {
+			/* if we can't stat current dir, bail */
+			if (stat(".", &st_pwd)) {
+				p(unknowndir);
+				return;
+			}
+			if (!stat(envpwd, &st_envpwd) && file_match(&st_pwd, &st_envpwd)) {
+				rpwd = mrpwd = envpwd;
+			}
+		} else {
+			/* invalidate envpwd so it can be used to determine if st_pwd was initialized */
+			envpwd = NULL;
+		}
 		/* strip HOME out if possible */
 		if (home) {
 			size_t l = strlen(home);
-			if (!strncmp(home, rpwd, l)) {
+			if (!strncmp(home, rpwd, l) && (rpwd[l] == 0 || rpwd[l] == '/')) {
 				/* found HOME in pwd */
 				p("~");
-				rpwd += l;
-				if (!*rpwd)
-					/* printing ~ is enough
-					 * if it goes on, it will print ~/ */
-					goto end;
+				/* advance both pwd pointers */
+				rpwd = (mrpwd += l);
+				/* check if we are in HOME.
+				 * if yes, printing '~' is all we want */
+				if (
+						/* pwd is only HOME */
+						rpwd[0] == 0 ||
+						/* current dir is HOME anyway */
+						!stat(home, &st_home) &&
+						(envpwd || !stat(".", &st_pwd)) && /* only stat(".") if it hasn't happened before */
+						file_match(&st_home, &st_pwd))
+					return;
 			}
 
-			if (fish_style_dir) {
-				/* short and sweet way of malloc-ing enough memory */
-				char *frpwd = strdup(rpwd);
+			/* starting from here, rpwd always starts with '/'.
+			 * it can be a path relative to HOME or an absolute path */
 
-				/* rpwd starts with a slash */
-				const char *c = rpwd, *co;
-				char *n = frpwd;
-				for (; c; co = c, c = strchr(co+1, '/')) {
-					*n++ = '/';
-					*n++ = *(c+1);
+			if (fish_style_dir) {
+				char *saveptr;
+				const char *tok, *oldtok = NULL;
+				while ((tok = strtok_r(mrpwd, "/", &saveptr))) {
+					mrpwd = NULL;
+					if (!strcmp(tok, "..")) {
+						p("/..");
+					} else {
+						char str[] = {'/', tok[0], 0};
+						p(str);
+					}
+
+					oldtok = tok;
+				}
+				/* print the last token in full */
+				if (oldtok)
+					p(oldtok+1);
+				/* if no token was found, we are in root */
+				if (mrpwd) {
+					p("/");
 				}
-				/* copy last path completely */
-				strcpy(--n, co+1);
-				p(frpwd);
-				free(frpwd);
 			} else {
 				p(rpwd);
 			}
@@ -51,7 +94,4 @@ void print_pwd(const char *home)
 			p(rpwd);
 		}
 	}
-
-end:
-	free(pwd);
 }