cmd/shfmt: support editorconfig language sections

That is, support `[[shell]]` EditorConfig sections when formatting
any shell file, and `[[bash]]` when formatting Bash files.

This is mainly helpful when formatting files with a shebang
but no extension, as then the formatter does use the right language
when parsing and formatting the code, but EditorConfig doesn't kick in
as it only knows how to match by filename per the spec.

This feature is out of the EditorConfig spec,
and upstream is tracking a feature like this at
editorconfig/editorconfig#404 since 2019.
Due to the lack of progress upstream, and how useful this feature
is for shfmt, go ahead and add it ourselves,
with a note that we may change or remove it at any time.

Fixes #664.

cmd/shfmt/main.go

@@ -320,7 +320,11 @@ func walkPath(path string, entry fs.DirEntry) error {
 		return filepath.SkipDir
 	}
 	if useEditorConfig {
-		props, err := ecQuery.Find(path)
+		// We don't know the language variant at this point yet, as we are walking directories
+		// and we first want to tell if we should skip a path entirely.
+		// TODO: Should the call to Find with the language name check "ignore" too, then?
+		// Otherwise a [[bash]] section with ignore=true is effectively never used.
+		props, err := ecQuery.Find(path, []string{"shell"})
 		if err != nil {
 			return err
 		}
@@ -420,9 +424,23 @@ func formatPath(path string, checkShebang bool) error {
 	return formatBytes(readBuf.Bytes(), path, fileLang)
 }
 
+func editorConfigLangs(l syntax.LangVariant) []string {
+	// All known shells match [[shell]].
+	// As a special case, bash and the bash-like bats also match [[bash]]
+	// We can later consider others like [[mksh]] or [[posix-shell]],
+	// just consider what list of languages the EditorConfig spec might eventually use.
+	switch l {
+	case syntax.LangBash, syntax.LangBats:
+		return []string{"shell", "bash"}
+	case syntax.LangPOSIX, syntax.LangMirBSDKorn, syntax.LangAuto:
+		return []string{"shell"}
+	}
+	return nil
+}
+
 func formatBytes(src []byte, path string, fileLang syntax.LangVariant) error {
 	if useEditorConfig {
-		props, err := ecQuery.Find(path)
+		props, err := ecQuery.Find(path, editorConfigLangs(fileLang))
 		if err != nil {
 			return err
 		}

cmd/shfmt/shfmt.1.scd

@@ -139,6 +139,10 @@ function_next_line = true
 ignore = true
 ```
 
+EditorConfig sections may also use `[[shell]]` or `[[bash]]` to match any shell or bash scripts,
+which is particularly useful when scripts use a shebang but no extension.
+Note that this feature is outside of the EditorConfig spec and may be changed in the future.
+
 shfmt can also replace *bash -n* to check shell scripts for syntax errors. It is
 more exhaustive, as it parses all syntax statically and requires valid UTF-8:
 

cmd/shfmt/testdata/script/editorconfig.txtar

@@ -53,6 +53,11 @@ stdout 'regular\.sh'
 ! stdout 'ignored\.sh'
 ! stderr .
 
+# Check EditorConfig [[language]] sections, used primarily for extension-less strings with shebangs.
+exec shfmt -d shebang
+! stdout .
+! stderr .
+
 -- .editorconfig --
 root = true
 
@@ -156,3 +161,29 @@ echo   foo
 echo   foo
 -- ignored/3_regular/regular.sh --
 echo   foo
+-- shebang/.editorconfig --
+root = true
+
+[*]
+indent_style = space
+indent_size = 1
+
+[[shell]]
+indent_size = 2
+
+[[bash]]
+indent_size = 4
+
+-- shebang/binsh --
+#!/bin/sh
+
+{
+  indented
+}
+-- shebang/binbash --
+#!/bin/bash
+
+{
+    indented
+}
+array=(elem)

go.mod

@@ -12,7 +12,7 @@ require (
 	golang.org/x/sync v0.5.0
 	golang.org/x/sys v0.15.0
 	golang.org/x/term v0.15.0
-	mvdan.cc/editorconfig v0.2.0
+	mvdan.cc/editorconfig v0.2.1-0.20231228180347-1925077f8eb2
 )
 
 require (

go.sum

@@ -25,5 +25,7 @@ golang.org/x/term v0.15.0 h1:y/Oo/a/q3IXu26lQgl04j/gjuBDOBlx7X6Om1j2CPW4=
 golang.org/x/term v0.15.0/go.mod h1:BDl952bC7+uMoWR75FIrCDx79TPU9oHkTZ9yRbYOrX0=
 golang.org/x/tools v0.1.12 h1:VveCTK38A2rkS8ZqFY25HIDFscX5X9OoEhJd3quQmXU=
 golang.org/x/tools v0.1.12/go.mod h1:hNGJHUnrk76NpqgfD5Aqm5Crs+Hm0VOH/i9J2+nxYbc=
-mvdan.cc/editorconfig v0.2.0 h1:XL+7ys6ls/RKrkUNFQvEwIvNHh+JKx8Mj1pUV5wQxQE=
-mvdan.cc/editorconfig v0.2.0/go.mod h1:lvnnD3BNdBYkhq+B4uBuFFKatfp02eB6HixDvEz91C0=
+mvdan.cc/editorconfig v0.2.1-0.20231227223507-ad7477e883b4 h1:SUMDYCoRUx5kuz3pkNWvsvpO0b4gN4pxXll47TsWHe0=
+mvdan.cc/editorconfig v0.2.1-0.20231227223507-ad7477e883b4/go.mod h1:r8RiQJRtzrPrZdcdEs5VCMqvRxAzYDUu9a4S9z7fKh8=
+mvdan.cc/editorconfig v0.2.1-0.20231228180347-1925077f8eb2 h1:8nmqQGVnHUtHuT+yvuA49lQK0y5il5IOr2PtCBkDI2M=
+mvdan.cc/editorconfig v0.2.1-0.20231228180347-1925077f8eb2/go.mod h1:r8RiQJRtzrPrZdcdEs5VCMqvRxAzYDUu9a4S9z7fKh8=