findprog-in: Make exec optimization optional.

* lib/findprog.h: Add double-inclusion guard. Include <stdbool.h>.
(find_in_given_path): Add optimize_for_exec parameter.
* lib/findprog-in.c (find_in_given_path): Likewise.

3 files changed, 97 insertions, 22 deletions

diff --git a/ChangeLog b/ChangeLog
index b2d2b00448..8ca2a33052 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,6 +1,13 @@
+2019-09-09  Bruno Haible  <bruno@clisp.org>
+
+	findprog-in: Make exec optimization optional.
+	* lib/findprog.h: Add double-inclusion guard. Include <stdbool.h>.
+	(find_in_given_path): Add optimize_for_exec parameter.
+	* lib/findprog-in.c (find_in_given_path): Likewise.
+
 2019-09-08  Bruno Haible  <bruno@clisp.org>
 
 	Add option to assume the best, not the worst, when cross-compiling.
 	Suggested by Jonas Termansen <sortie@maxsi.org>.
 	* m4/gnulib-common.m4 (gl_COMMON_BODY): Add --enable-cross-guesses=...
 	option. Set gl_cross_guess_normal and gl_cross_guess_inverted.
diff --git a/lib/findprog-in.c b/lib/findprog-in.c
index 3d70b7b393..99b3c314d9 100644
--- a/lib/findprog-in.c
+++ b/lib/findprog-in.c
@@ -68,32 +68,90 @@ static const char * const suffixes[] =
     #else /* Unix */
     ""
     #endif
   };
 
 const char *
-find_in_given_path (const char *progname, const char *path)
+find_in_given_path (const char *progname, const char *path,
+                    bool optimize_for_exec)
 {
   {
     bool has_slash = false;
-    const char *p;
+    {
+      const char *p;
 
-    for (p = progname; *p != '\0'; p++)
-      if (ISSLASH (*p))
-        {
-          has_slash = true;
-          break;
-        }
+      for (p = progname; *p != '\0'; p++)
+        if (ISSLASH (*p))
+          {
+            has_slash = true;
+            break;
+          }
+    }
     if (has_slash)
-      /* If progname contains a slash, it is either absolute or relative to
-         the current directory.  PATH is not used.
-         We could try the various suffixes and see whether one of the files
-         with such a suffix is actually executable.  But this is not needed,
-         since the execl/execv/execlp/execvp functions will do these tests
-         anyway.  */
-      return progname;
+      {
+        /* If progname contains a slash, it is either absolute or relative to
+           the current directory.  PATH is not used.  */
+        if (optimize_for_exec)
+          /* The execl/execv/execlp/execvp functions will try the various
+             suffixes anyway and fail if no executable is found.  */
+          return progname;
+        else
+          {
+            /* Try the various suffixes and see whether one of the files
+               with such a suffix is actually executable.  */
+            size_t i;
+            #if defined _WIN32 && !defined __CYGWIN__ /* Native Windows */
+            const char *progbasename;
+
+            {
+              const char *p;
+
+              progbasename = progname;
+              for (p = progname; *p != '\0'; p++)
+                if (ISSLASH (*p))
+                  progbasename = p + 1;
+            }
+            #endif
+
+            /* Try all platform-dependent suffixes.  */
+            for (i = 0; i < sizeof (suffixes) / sizeof (suffixes[0]); i++)
+              {
+                const char *suffix = suffixes[i];
+
+                #if defined _WIN32 && !defined __CYGWIN__ /* Native Windows */
+                /* File names without a '.' are not considered executable.  */
+                if (*suffix != '\0' || strchr (progbasename, '.') != NULL)
+                #endif
+                  {
+                    /* Concatenate progname and suffix.  */
+                    char *progpathname =
+                      xconcatenated_filename ("", progname, suffix);
+
+                    /* On systems which have the eaccess() system call, let's
+                       use it.  On other systems, let's hope that this program
+                       is not installed setuid or setgid, so that it is ok to
+                       call access() despite its design flaw.  */
+                    if (eaccess (progpathname, X_OK) == 0)
+                      {
+                        /* Found!  */
+                        if (strcmp (progpathname, progname) == 0)
+                          {
+                            free (progpathname);
+                            return progname;
+                          }
+                        else
+                          return progpathname;
+                      }
+
+                    free (progpathname);
+                  }
+              }
+
+            return NULL;
+          }
+      }
   }
 
   if (path == NULL)
     /* If PATH is not set, the default search path is implementation dependent.
        In practice, it is treated like an empty PATH.  */
     path = "";
@@ -128,20 +186,20 @@ find_in_given_path (const char *progname, const char *path)
 
             #if defined _WIN32 && !defined __CYGWIN__ /* Native Windows */
             /* File names without a '.' are not considered executable.  */
             if (*suffix != '\0' || strchr (progname, '.') != NULL)
             #endif
               {
-                /* Concatenate dir and progname.  */
+                /* Concatenate dir, progname, and suffix.  */
                 char *progpathname =
                   xconcatenated_filename (dir, progname, suffix);
 
-                /* On systems which have the eaccess() system call, let's use
-                   it.  On other systems, let's hope that this program is not
-                   installed setuid or setgid, so that it is ok to call
-                   access() despite its design flaw.  */
+                /* On systems which have the eaccess() system call, let's
+                   use it.  On other systems, let's hope that this program
+                   is not installed setuid or setgid, so that it is ok to
+                   call access() despite its design flaw.  */
                 if (eaccess (progpathname, X_OK) == 0)
                   {
                     /* Found!  */
                     if (strcmp (progpathname, progname) == 0)
                       {
                         free (progpathname);
diff --git a/lib/findprog.h b/lib/findprog.h
index 9bc8a60da2..f7b44071fb 100644
--- a/lib/findprog.h
+++ b/lib/findprog.h
@@ -12,12 +12,16 @@
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.
 
    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
 
+#ifndef _FINDPROG_H
+#define _FINDPROG_H
+
+#include <stdbool.h>
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
 
@@ -38,13 +42,19 @@ extern const char *find_in_path (const char *progname);
    singleton list that contains only the current directory.
    Determines the pathname that would be called by execlp/execvp of PROGNAME.
    - If successful, it returns a pathname containing a slash (either absolute
      or relative to the current directory).  The returned string can be used
      with either execl/execv or execlp/execvp.  It is freshly malloc()ed if it
      is != PROGNAME.
-   - Otherwise, it returns NULL.  */
-extern const char *find_in_given_path (const char *progname, const char *path);
+   - Otherwise, it returns NULL.
+   If OPTIMIZE_FOR_EXEC is true, the function saves some work, under the
+   assumption that the resulting pathname will not be accessed directly,
+   only through execl/execv or execlp/execvp.  */
+extern const char *find_in_given_path (const char *progname, const char *path,
+                                       bool optimize_for_exec);
 
 
 #ifdef __cplusplus
 }
 #endif
+
+#endif /* _FINDPROG_H */