cmd/shfmt: add a way to ignore directory entries when walking

This piggybacks on v3's EditorConfig feature, obeying the "ignore =
true" property.

The provided example uses a "/**" suffix, since that's the best way to
match a directory sub-tree right now. "third_party" alone could match a
non-directory with that name, and EditorConfig doesn't support patterns
like "third_party/". We could add support for that later if needed.

Once a directory is ignored, it's not walked at all. This way, huge
directories containing uninteresting files can be skipped entirely.

Fixes #288.

README.md

@@ -55,6 +55,10 @@ binary_next_line   = true  # like -bn
 switch_case_indent = true  # like -ci
 space_redirects    = true  # like -sr
 keep_padding       = true  # like -kp
+
+# Ignore the entire "third_party" directory.
+[third_party/**]
+ignore = true
 ```
 
 Packages are available on [Alpine], [Arch], [Docker], [FreeBSD], [Homebrew],

cmd/shfmt/main.go

@@ -215,6 +215,19 @@ func walk(path string, onError func(error)) {
 		if info.IsDir() && vcsDir.MatchString(info.Name()) {
 			return filepath.SkipDir
 		}
+		if useEditorConfig {
+			props, err := ecQuery.Find(path)
+			if err != nil {
+				return err
+			}
+			if props.Get("ignore") == "true" {
+				if info.IsDir() {
+					return filepath.SkipDir
+				} else {
+					return nil
+				}
+			}
+		}
 		conf := fileutil.CouldBeScript(info)
 		if conf == fileutil.ConfNotScript {
 			return nil
@@ -227,7 +240,7 @@ func walk(path string, onError func(error)) {
 	})
 }
 
-var query = editorconfig.Query{
+var ecQuery = editorconfig.Query{
 	FileCache:   make(map[string]*editorconfig.File),
 	RegexpCache: make(map[string]*regexp.Regexp),
 }
@@ -287,7 +300,7 @@ func formatPath(path string, checkShebang bool) error {
 
 func formatBytes(src []byte, path string) error {
 	if useEditorConfig {
-		props, err := query.Find(path)
+		props, err := ecQuery.Find(path)
 		if err != nil {
 			return err
 		}

cmd/shfmt/testdata/scripts/editorconfig.txt

@@ -39,6 +39,12 @@ shfmt -l otherknobs
 ! stdout .
 ! stderr .
 
+# Ignore directories when walking, if they match ignore=true.
+shfmt -l ignored
+stdout 'regular\.sh'
+! stdout 'ignored\.sh'
+! stderr .
+
 -- .editorconfig --
 root = true
 
@@ -107,3 +113,23 @@ esac
 echo foo > bar
 -- otherknobs/keep_padding.sh --
 echo  foo    bar
+-- ignored/.editorconfig --
+root = true
+
+[third_party/**]
+ignore = true
+
+[1_lone_ignored.sh]
+ignore = true
+
+[2_dir_ignored]
+ignore = true
+
+-- ignored/third_party/ignored.sh --
+bad (syntax
+-- ignored/1_lone_ignored.sh
+echo   foo
+-- ignored/2_dir_ignored/ignored.sh --
+echo   foo
+-- ignored/3_regular/regular.sh --
+echo   foo