feat: add slim output

docs/command-usage.md

@@ -90,7 +90,7 @@ The string array flags can be a bit confusing. See the [String Array Flags](#str
 | KYAML                 | `-kyaml`              | bool              | `yamlfmat -kyaml`                                         | Enable the alternate [KYAML formatter](./config-file.md#kyaml-formatter). Note that using this option will completely override any formatter configuration from detected config file. |
 | Formatter Config      | `-formatter`          | []string          | `yamlfmt -formatter indent=2,include_document_start=true` | Provide configuration values for the formatter. See [Formatter Configuration Options](./config-file.md#basic-formatter) for options. Each field is specified as `configkey=value`. |
 | Debug Logging         | `-debug`              | []string          | `yamlfmt -debug paths,config`                             | Enable debug logging. See [Debug Logging](#debug-logging) for more information. |
-| Output Format         | `-output_format`      | `default`, `line` | `yamlfmt -output_format line`                             | Choose a different output format. Defaults to `default`. See [Output docs](./output.md) for more information. |
+| Output Format         | `-output_format`      | `default`, `line`, `slim`, `gitlab` | `yamlfmt -output_format slim`                             | Choose a different output format. Defaults to `default`. See [Output docs](./output.md) for more information. |
 
 #### String Array Flags
 

docs/config-file.md

@@ -47,7 +47,7 @@ The command package defines the main command engine that `cmd/yamlfmt` uses. It
 | `regex_exclude`          | []string            | []            | Regex patterns to match file contents for, if the file content matches the regex the file will be excluded. Use [Go regexes](https://regex101.com/). |
 | `extensions`             | []string            | []            | The extensions to use for standard mode path collection. See [Specifying Paths][] for more details. |
 | `formatter`              | map[string]any      | `type: basic` | Formatter settings. See [Formatter](#formatter) for more details. |
-| `output_format`          | `default` or `line` | `default`     | The output format to use. See [Output docs](./output.md) for more details. |
+| `output_format`          | `default`, `line`, `slim`, or `gitlab` | `default`     | The output format to use. See [Output docs](./output.md) for more details. |
 
 ## Formatter
 

docs/output.md

@@ -33,6 +33,22 @@ y.yaml: formatting difference found
 z.yaml: formatting difference found
 ```
 
+## `slim`
+
+Prints a unified diff with nearby context lines instead of the full side-by-side file view.
+
+Example:
+```
+The following formatting differences were found:
+
+--- x.yaml
++++ x.yaml
+@@ -1,2 +1,2 @@
+ a:
+- b:1
++ b: 1
+```
+
 ## `gitlab`
 
 Generates a [GitLab Code Quality report](https://docs.gitlab.com/ee/ci/testing/code_quality.html#code-quality-report-format).

engine.go

@@ -113,7 +113,7 @@ func (fds FileDiffs) Add(diff *FileDiff) error {
 
 func (fds FileDiffs) StrOutput() string {
 	result := ""
-	sortedPaths := fds.sortedPaths()
+	sortedPaths := fds.SortedPaths()
 	for _, path := range sortedPaths {
 		fd := fds[path]
 		if fd.Diff.Changed() {
@@ -125,7 +125,7 @@ func (fds FileDiffs) StrOutput() string {
 
 func (fds FileDiffs) StrOutputQuiet() string {
 	result := ""
-	sortedPaths := fds.sortedPaths()
+	sortedPaths := fds.SortedPaths()
 	for _, path := range sortedPaths {
 		fd := fds[path]
 		if fd.Diff.Changed() {
@@ -155,7 +155,7 @@ func (fds FileDiffs) ChangedCount() int {
 	return changed
 }
 
-func (fds FileDiffs) sortedPaths() []string {
+func (fds FileDiffs) SortedPaths() []string {
 	pathKeys := []string{}
 	for path := range fds {
 		pathKeys = append(pathKeys, path)

engine/output.go

@@ -22,13 +22,17 @@ import (
 
 	"github.com/google/yamlfmt"
 	"github.com/google/yamlfmt/internal/gitlab"
+	"github.com/hexops/gotextdiff"
+	"github.com/hexops/gotextdiff/myers"
+	"github.com/hexops/gotextdiff/span"
 )
 
 type EngineOutputFormat string
 
 const (
 	EngineOutputDefault   EngineOutputFormat = "default"
 	EngineOutputSingeLine EngineOutputFormat = "line"
+	EngineOutputSlim      EngineOutputFormat = "slim"
 	EngineOutputGitlab    EngineOutputFormat = "gitlab"
 )
 
@@ -38,6 +42,8 @@ func getEngineOutput(t EngineOutputFormat, operation yamlfmt.Operation, files ya
 		return engineOutput{Operation: operation, Files: files, Quiet: quiet, Verbose: verbose}, nil
 	case EngineOutputSingeLine:
 		return engineOutputSingleLine{Operation: operation, Files: files, Quiet: quiet}, nil
+	case EngineOutputSlim:
+		return engineOutputSlim{Operation: operation, Files: files, Quiet: quiet, Verbose: verbose}, nil
 	case EngineOutputGitlab:
 		return engineOutputGitlab{Operation: operation, Files: files, Compact: quiet}, nil
 
@@ -104,6 +110,70 @@ func (eosl engineOutputSingleLine) String() string {
 	return msg
 }
 
+type engineOutputSlim struct {
+	Operation yamlfmt.Operation
+	Files     yamlfmt.FileDiffs
+	Quiet     bool
+	Verbose   bool
+}
+
+func (eos engineOutputSlim) String() string {
+	var msg string
+	switch eos.Operation {
+	case yamlfmt.OperationFormat:
+		// Formatting only produces output in verbose mode.
+		if !eos.Verbose {
+			return ""
+		}
+		msg = "The following files were modified:"
+	case yamlfmt.OperationLint:
+		msg = "The following formatting differences were found:"
+		if eos.Quiet {
+			msg = "The following files had formatting differences:"
+		}
+	case yamlfmt.OperationDry:
+		if eos.Files.ChangedCount() == 0 {
+			return "No files will be formatted."
+		}
+		msg = "The following files would be formatted:"
+	}
+
+	var b strings.Builder
+	if msg != "" {
+		b.WriteString(msg + "\n\n")
+	}
+
+	if eos.Quiet {
+		b.WriteString(eos.Files.StrOutputQuiet())
+		return b.String()
+	}
+
+	for _, fileDiff := range eos.changedFileDiffs() {
+		output := slimFileDiff(fileDiff)
+		b.WriteString(output)
+	}
+	return b.String()
+}
+
+func (eos engineOutputSlim) changedFileDiffs() []*yamlfmt.FileDiff {
+	changed := make([]*yamlfmt.FileDiff, 0, eos.Files.ChangedCount())
+	for _, path := range eos.Files.SortedPaths() {
+		fileDiff := eos.Files[path]
+		if !fileDiff.Diff.Changed() {
+			continue
+		}
+		changed = append(changed, fileDiff)
+	}
+	return changed
+}
+
+func slimFileDiff(fileDiff *yamlfmt.FileDiff) string {
+	original := fileDiff.Diff.GetOriginal()
+	formatted := fileDiff.Diff.GetFormatted()
+	edits := myers.ComputeEdits(span.URIFromPath(fileDiff.Path), original, formatted)
+	return fmt.Sprint(gotextdiff.ToUnified(fileDiff.Path, fileDiff.Path, original, edits))
+}
+
 type engineOutputGitlab struct {
 	Operation yamlfmt.Operation
 	Files     yamlfmt.FileDiffs

go.mod

@@ -7,6 +7,7 @@ toolchain go1.24.8
 require (
 	github.com/bmatcuk/doublestar/v4 v4.7.1
 	github.com/google/go-cmp v0.6.0
+	github.com/hexops/gotextdiff v1.0.3
 	github.com/mitchellh/mapstructure v1.5.0
 	github.com/sabhiram/go-gitignore v0.0.0-20210923224102-525f6e181f06
 	github.com/santhosh-tekuri/jsonschema/v6 v6.0.1

go.sum

@@ -7,6 +7,8 @@ github.com/dlclark/regexp2 v1.11.0 h1:G/nrcoOa7ZXlpoa/91N3X7mM3r8eIlMBBJZvsz/mxK
 github.com/dlclark/regexp2 v1.11.0/go.mod h1:DHkYz0B9wPfa6wondMfaivmHpzrQ3v9q8cnmRbL6yW8=
 github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
 github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
+github.com/hexops/gotextdiff v1.0.3 h1:gitA9+qJrrTCsiCl7+kh75nPqQt1cx4ZkudSTLoUqJM=
+github.com/hexops/gotextdiff v1.0.3/go.mod h1:pSWU5MAI3yDq+fZBTazCSJysOMbxWL1BSow5/V2vxeg=
 github.com/mitchellh/mapstructure v1.5.0 h1:jeMsZIYE/09sWLaz43PL7Gy6RuMjD2eJVyuac5Z2hdY=
 github.com/mitchellh/mapstructure v1.5.0/go.mod h1:bFUtVrKA4DC2yAKiSyO/QUcy7e+RRV2QTWOzhPopBRo=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=

integrationtest/command/command_test.go

@@ -93,6 +93,15 @@ func TestDry(t *testing.T) {
 	}.Run(t)
 }
 
+func TestSlimOutput(t *testing.T) {
+	TestCase{
+		Dir:     "slim_output",
+		Command: yamlfmtWithArgs("-lint -output_format slim ."),
+		Update:  *updateFlag,
+		IsError: true,
+	}.Run(t)
+}
+
 func TestDryQuiet(t *testing.T) {
 	TestCase{
 		Dir:     "dry_quiet",

integrationtest/command/testdata/slim_output/after/x.yaml

@@ -0,0 +1,2 @@
+a:
+  b : 1

integrationtest/command/testdata/slim_output/before/x.yaml

@@ -0,0 +1,2 @@
+a:
+  b : 1

integrationtest/command/testdata/slim_output/stdout/stderr.txt

@@ -0,0 +1,8 @@
+The following formatting differences were found:
+
+--- x.yaml
++++ x.yaml
+@@ -1,2 +1,2 @@
+ a:
+-  b : 1
++  b: 1

schema.json

@@ -83,7 +83,9 @@
       "type": "string",
       "enum": [
         "default",
-        "line"
+        "line",
+        "slim",
+        "gitlab"
       ],
       "default": "default",
       "description": "The output format to use. See Output docs for more details."