Add eof_newline option

This PR adds a new option to forcibly add the end of file newline if
it's not there. This is useful in the scenario where the
`retain_line_breaks` feature is disabled but the eof newline is still
wanted.

docs/config-file.md

@@ -82,7 +82,8 @@ The basic formatter is a barebones formatter that simply takes the data provided
 | `indentless_arrays`         | bool           | false   | Render `-` array items (block sequence items) without an increased indent. |
 | `drop_merge_tag`            | bool           | false   | Assume that any well formed merge using just a `<<` token will be a merge, and drop the `!!merge` tag from the formatted result. |
 | `pad_line_comments`         | int            | 1       | The number of padding spaces to insert before line comments. |
-| `trim_trailing_whitespace`  | bool           | false   | Whether to trim trailing whitespace from lines. |
+| `trim_trailing_whitespace`  | bool           | false   | Trim trailing whitespace from lines. |
+| `eof_newline`               | bool           | false   | Always add a newline at end of file. Useful in the scenario where `retain_line_breaks` is disabled but the trailing newline is still needed. |
 
 ### Note on `max_line_length`
 

formatters/basic/config.go

@@ -33,6 +33,7 @@ type Config struct {
 	DropMergeTag           bool                   `mapstructure:"drop_merge_tag"`
 	PadLineComments        int                    `mapstructure:"pad_line_comments"`
 	TrimTrailingWhitespace bool                   `mapstructure:"trim_trailing_whitespace"`
+	EOFNewline             bool                   `mapstructure:"eof_newline"`
 }
 
 func DefaultConfig() *Config {

formatters/basic/features.go

@@ -18,29 +18,35 @@ import (
 	"github.com/braydonk/yaml"
 	"github.com/google/yamlfmt"
 	"github.com/google/yamlfmt/formatters/basic/anchors"
+	"github.com/google/yamlfmt/internal/features"
 	"github.com/google/yamlfmt/internal/hotfix"
-	"github.com/google/yamlfmt/internal/trim"
 )
 
 func ConfigureFeaturesFromConfig(config *Config) yamlfmt.FeatureList {
 	lineSep, err := config.LineEnding.Separator()
 	if err != nil {
 		lineSep = "\n"
 	}
-	features := []yamlfmt.Feature{}
+	configuredFeatures := []yamlfmt.Feature{}
 	if config.RetainLineBreaks || config.RetainLineBreaksSingle {
-		features = append(
-			features,
+		configuredFeatures = append(
+			configuredFeatures,
 			hotfix.MakeFeatureRetainLineBreak(lineSep, config.RetainLineBreaksSingle),
 		)
 	}
 	if config.TrimTrailingWhitespace {
-		features = append(
-			features,
-			trim.MakeFeatureTrimTrailingWhitespace(lineSep),
+		configuredFeatures = append(
+			configuredFeatures,
+			features.MakeFeatureTrimTrailingWhitespace(lineSep),
 		)
 	}
-	return features
+	if config.EOFNewline {
+		configuredFeatures = append(
+			configuredFeatures,
+			features.MakeFeatureEOFNewline(lineSep),
+		)
+	}
+	return configuredFeatures
 }
 
 // These features will directly use the `yaml.Node` type and

formatters/basic/formatter_test.go

@@ -329,3 +329,25 @@ b: 2`
 		t.Fatalf("expected: '%s', got: '%s'", expectedYml, resultStr)
 	}
 }
+
+func TestEOFNewline(t *testing.T) {
+	config := basic.DefaultConfig()
+	config.RetainLineBreaks = false
+	config.EOFNewline = true
+	f := newFormatter(config)
+
+	yml := `a: 1
+b: 2`
+	expectedYml := `a: 1
+b: 2
+`
+
+	result, err := f.Format([]byte(yml))
+	if err != nil {
+		t.Fatalf("expected formatting to pass, returned error: %v", err)
+	}
+	resultStr := string(result)
+	if resultStr != expectedYml {
+		t.Fatalf("expected: '%s', got: '%s'", expectedYml, resultStr)
+	}
+}

integrationtest/command/command_test.go

@@ -131,3 +131,11 @@ func TestMultilineStringBug(t *testing.T) {
 		Update:  *updateFlag,
 	}.Run(t)
 }
+
+func TestEOFNewline(t *testing.T) {
+	TestCase{
+		Dir:     "eof_newline",
+		Command: yamlfmtWithArgs("-formatter eof_newline=true ."),
+		Update:  *updateFlag,
+	}.Run(t)
+}

integrationtest/command/testdata/eof_newline/after/a.yaml

@@ -0,0 +1,2 @@
+# no newline at end
+a: 1

integrationtest/command/testdata/eof_newline/before/a.yaml

@@ -0,0 +1,2 @@
+# no newline at end
+a: 1

integrationtest/command/testdata/print_conf_file/stdout/stdout.txt

@@ -14,6 +14,7 @@ regex_exclude: []
 formatter:
     disallow_anchors: false
     drop_merge_tag: false
+    eof_newline: false
     include_document_start: true
     indent: 2
     indentless_arrays: false

integrationtest/command/testdata/print_conf_flags/stdout/stdout.txt

@@ -13,6 +13,7 @@ regex_exclude: []
 formatter:
     disallow_anchors: false
     drop_merge_tag: false
+    eof_newline: false
     include_document_start: false
     indent: 2
     indentless_arrays: false

integrationtest/command/testdata/print_conf_flags_and_file/stdout/stdout.txt

@@ -14,6 +14,7 @@ regex_exclude: []
 formatter:
     disallow_anchors: false
     drop_merge_tag: false
+    eof_newline: false
     include_document_start: true
     indent: 2
     indentless_arrays: false

internal/features/eof_newline.go

@@ -0,0 +1,37 @@
+// Copyright 2024 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package features
+
+import (
+	"github.com/google/yamlfmt"
+)
+
+func MakeFeatureEOFNewline(linebreakStr string) yamlfmt.Feature {
+	return yamlfmt.Feature{
+		Name:        "EOF Newline",
+		AfterAction: eofNewlineFeature(linebreakStr),
+	}
+}
+
+func eofNewlineFeature(linebreakStr string) yamlfmt.FeatureFunc {
+	return func(content []byte) ([]byte, error) {
+		// This check works in both linebreak modes.
+		if content[len(content)-1] != '\n' {
+			linebreakBytes := []byte(linebreakStr)
+			content = append(content, linebreakBytes...)
+		}
+		return content, nil
+	}
+}

internal/trim/trim_whitespace.go → internal/features/trim_whitespace.go

@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package trim
+package features
 
 import (
 	"bufio"