util.executable.which: handle path separators like /bin/which (#17668)

* util.executable.which: handle path separators like /bin/which

Co-authored-by: Massimiliano Culpo <massimiliano.culpo@gmail.com>

lib/spack/spack/test/util/executable.py

@@ -40,6 +40,36 @@ def test_read_unicode(tmpdir, working_env):
         assert u'\xc3' == script(output=str).strip()
 
 
+def test_which_relative_path_with_slash(tmpdir, working_env):
+    tmpdir.ensure('exe')
+    path = str(tmpdir.join('exe'))
+    os.environ['PATH'] = ''
+
+    with tmpdir.as_cwd():
+        no_exe = ex.which('./exe')
+        assert no_exe is None
+
+        fs.set_executable(path)
+        exe = ex.which('./exe')
+        assert exe.path == path
+
+
+def test_which_with_slash_ignores_path(tmpdir, working_env):
+    tmpdir.ensure('exe')
+    tmpdir.ensure('bin{0}exe'.format(os.path.sep))
+
+    path = str(tmpdir.join('exe'))
+    wrong_path = str(tmpdir.join('bin', 'exe'))
+    os.environ['PATH'] = os.path.dirname(wrong_path)
+
+    fs.set_executable(path)
+    fs.set_executable(wrong_path)
+
+    with tmpdir.as_cwd():
+        exe = ex.which('./exe')
+        assert exe.path == path
+
+
 def test_which(tmpdir):
     os.environ["PATH"] = str(tmpdir)
     assert ex.which("spack-test-exe") is None

lib/spack/spack/util/executable.py

@@ -233,10 +233,15 @@ def which_string(*args, **kwargs):
         path = path.split(os.pathsep)
 
     for name in args:
-        for directory in path:
-            exe = os.path.join(directory, name)
+        if os.path.sep in name:
+            exe = os.path.abspath(name)
             if os.path.isfile(exe) and os.access(exe, os.X_OK):
                 return exe
+        else:
+            for directory in path:
+                exe = os.path.join(directory, name)
+                if os.path.isfile(exe) and os.access(exe, os.X_OK):
+                    return exe
 
     if required:
         raise CommandNotFoundError(