hooks: Fail ReadDir if a configured hook executable is missing

The continue here is from 5676597f (hooks/read: Ignore IsNotExist for
JSON files in ReadDir, 2018-04-27, #686), where it was intended to
silently ignore missing JSON files.  However, the old logic was also
silently ignoring not-exist errors from the os.Stat(hook.Hook.Path)
from 68eb128f (pkg/hooks: Version the hook structure and add 1.0.0
hooks, 2018-04-27, #686).  This commit adjusts the check so JSON
not-exist errors continue to be silently ignored while hook executable
not-exist errors become fatal.

Signed-off-by: W. Trevor King <wking@tremily.us>

Closes: #887
Approved by: rhatdan

pkg/hooks/read.go

@@ -67,13 +67,16 @@ func ReadDir(path string, extensionStages []string, hooks map[string]*current.Ho
 	}
 
 	for _, file := range files {
-		hook, err := Read(filepath.Join(path, file.Name()), extensionStages)
+		filePath := filepath.Join(path, file.Name())
+		hook, err := Read(filePath, extensionStages)
 		if err != nil {
 			if err == ErrNoJSONSuffix {
 				continue
 			}
 			if os.IsNotExist(err) {
-				continue
+				if err2, ok := err.(*os.PathError); ok && err2.Path == filePath {
+					continue
+				}
 			}
 			return err
 		}

pkg/hooks/read_test.go

@@ -191,3 +191,24 @@ func TestBadDir(t *testing.T) {
 	}
 	assert.Regexp(t, "^parsing hook \"[^\"]*a.json\": unrecognized hook version: \"-1\"$", err.Error())
 }
+
+func TestHookExecutableDoesNotExit(t *testing.T) {
+	dir, err := ioutil.TempDir("", "hooks-test-")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(dir)
+
+	jsonPath := filepath.Join(dir, "hook.json")
+	err = ioutil.WriteFile(jsonPath, []byte("{\"version\": \"1.0.0\", \"hook\": {\"path\": \"/does/not/exist\"}, \"when\": {\"always\": true}, \"stages\": [\"prestart\"]}"), 0644)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	hooks := map[string]*current.Hook{}
+	err = ReadDir(dir, []string{}, hooks)
+	if err == nil {
+		t.Fatal("unexpected success")
+	}
+	assert.Regexp(t, "^stat /does/not/exist: no such file or directory$", err.Error())
+}