win32: another BB_OVERRIDE_APPLETS fix

Support for conditionally replacing applets with external commands
requires the ability to check whether a given command name is
present on PATH.  This was being done using the PATH environment
variable, which works in commands run by the shell but not in the
shell itself.

- The shell uses the *shell* variable PATH to look for executables.
  This may not be the same as the *environment* variable.

- 'command -p' uses an entirely different PATH.

Applet look-up in the shell is now treated as a special case, with
the actual PATH being used passed to the look-up code in a global
variable.

This doesn't affect tab completion in the shell:  whether a
completion is an applet or an external command is irrelevant.

Costs 152-288 bytes.

(GitHub issue #329)

3 files changed, 48 insertions, 6 deletions

diff --git a/include/libbb.h b/include/libbb.h
index a4eebab99..1200e636a 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -1330,6 +1330,9 @@ int find_preferred_applet_by_name(const char *name) FAST_FUNC;
 int is_applet_preferred(const char *name) FAST_FUNC;
 # if ENABLE_PLATFORM_MINGW32 && \
                 (ENABLE_FEATURE_PREFER_APPLETS || ENABLE_FEATURE_SH_STANDALONE)
+#  if ENABLE_ASH
+extern const char *ash_path;
+#  endif
 #  define find_applet_by_name(n) find_preferred_applet_by_name(n)
 # else
 #  define is_applet_preferred(n) (1)
diff --git a/libbb/appletlib.c b/libbb/appletlib.c
index b5ea90ffd..10268b982 100644
--- a/libbb/appletlib.c
+++ b/libbb/appletlib.c
@@ -263,9 +263,16 @@ int FAST_FUNC find_applet_by_name(const char *name)
 
 #if ENABLE_PLATFORM_MINGW32 && NUM_APPLETS > 1 && \
                 (ENABLE_FEATURE_PREFER_APPLETS || ENABLE_FEATURE_SH_STANDALONE)
+# if ENABLE_ASH
+const char *ash_path = NULL;
+# else
+#  define ash_path NULL
+# endif
+
 static int external_exists(const char *name)
 {
-        char *ret = find_first_executable(name);
+        char *path = ash_path ? auto_string(xstrdup(ash_path)) : getenv("PATH");
+        char *ret = find_executable(name, &path);
         free(ret);
         return ret != NULL;
 }
diff --git a/shell/ash.c b/shell/ash.c
index 07319dbdf..7fa75721e 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -426,6 +426,38 @@ static void forkshell_print(FILE *fp0, struct forkshell *fs, const char **notes)
 # endif
 #endif
 
+#if ENABLE_PLATFORM_MINGW32 && NUM_APPLETS > 1 && \
+                (ENABLE_FEATURE_PREFER_APPLETS || ENABLE_FEATURE_SH_STANDALONE)
+static int
+ash_preferred_applet_by_name(const char *name, const char *path)
+{
+        int ret;
+
+        ash_path = path;
+        ret = find_preferred_applet_by_name(name);
+        ash_path = NULL;
+
+        return ret;
+}
+
+static int
+ash_applet_preferred(const char *name, const char *path)
+{
+        int ret;
+
+        ash_path = path;
+        ret = is_applet_preferred(name);
+        ash_path = NULL;
+
+        return ret;
+}
+# undef find_applet_by_name
+# define find_applet_by_name(n, p) ash_preferred_applet_by_name(n, p)
+# define is_applet_preferred(n, p) ash_applet_preferred(n, p)
+#else
+# define find_applet_by_name(n, p) find_applet_by_name(n)
+#endif
+
 /* ============ Hash table sizes. Configurable. */
 
 #define VTABSIZE 39
@@ -9113,7 +9145,7 @@ static void shellexec(char *prog, char **argv, const char *path, int idx)
         if (has_path(prog)
 #endif
 #if ENABLE_FEATURE_SH_STANDALONE
-         || (applet_no = find_applet_by_name(prog)) >= 0
+         || (applet_no = find_applet_by_name(prog, path)) >= 0
 #endif
         ) {
 #if ENABLE_PLATFORM_MINGW32
@@ -9134,7 +9166,7 @@ static void shellexec(char *prog, char **argv, const char *path, int idx)
                 if (unix_path(prog)) {
                         const char *name = bb_basename(prog);
 # if ENABLE_FEATURE_SH_STANDALONE
-                        if ((applet_no = find_applet_by_name(name)) >= 0) {
+                        if ((applet_no = find_applet_by_name(name, path)) >= 0) {
                                 tryexec(applet_no, name, argv, envp);
                                 e = errno;
                         }
@@ -14939,7 +14971,7 @@ find_command(char *name, struct cmdentry *entry, int act, const char *path)
                         name = (char *)bb_basename(name);
                         if (
 # if ENABLE_FEATURE_SH_STANDALONE
-                                        find_applet_by_name(name) >= 0 ||
+                                        find_applet_by_name(name, path) >= 0 ||
 # endif
                                         !find_builtin(bb_basename(name))
                         ) {
@@ -15010,7 +15042,7 @@ find_command(char *name, struct cmdentry *entry, int act, const char *path)
 
 #if ENABLE_FEATURE_SH_STANDALONE
         {
-                int applet_no = find_applet_by_name(name);
+                int applet_no = find_applet_by_name(name, path);
                 if (applet_no >= 0) {
                         entry->cmdtype = CMDNORMAL;
                         entry->u.index = -2 - applet_no;
@@ -15259,7 +15291,7 @@ helpcmd(int argc UNUSED_PARAM, char **argv UNUSED_PARAM)
         {
                 const char *a = applet_names;
                 while (*a) {
-                        if (is_applet_preferred(a)) {
+                        if (is_applet_preferred(a, pathval())) {
                                 col += out1fmt("%c%s", ((col == 0) ? '\t' : ' '), a);
                                 if (col > 60) {
                                         out1fmt("\n");