In output-mode inject do not fail if file not found

The following scenarios can happen for --output-mode inject:

- file exists, comments exist: inject output between comments
- file exists, comments not found: append output at the end of file
- file exists, but empty: save the whole output into the file
- file not found: create the target file and save the ooutput into it

Signed-off-by: Khosrow Moossavi <khos2ow@gmail.com>

docs/user-guide/configuration.md

@@ -185,9 +185,9 @@ flag) is not empty. Insersion behavior can be controlled by `output.mode` (or
 
 - `inject` (default)
 
-  Partially replace the `output-file` with generated output. This will fail if
-  `output-file` doesn't exist. Also will fail if `output-file` doesn't already
-  have surrounding comments.
+  Partially replace the `output-file` with generated output. This will create
+  the `output-file` if it doesn't exist. It will also append to `output-file`
+  if it doesn't have surrounding comments.
 
 - `replace`
 

internal/cli/testdata/writer/mode-inject-empty-file.golden

@@ -0,0 +1,3 @@
+<!-- BEGIN_TF_DOCS -->
+Lorem ipsum dolor sit amet, consectetur adipiscing elit
+<!-- END_TF_DOCS -->

internal/cli/testdata/writer/mode-inject-file-missing.golden

@@ -0,0 +1,3 @@
+<!-- BEGIN_TF_DOCS -->
+Lorem ipsum dolor sit amet, consectetur adipiscing elit
+<!-- END_TF_DOCS -->

internal/cli/testdata/writer/mode-inject-no-comment.golden

@@ -0,0 +1,22 @@
+# Foo
+
+Lorem ipsum dolor sit amet, consectetur adipiscing elit.
+
+## Bar
+
+sed do eiusmod tempor incididunt ut labore et dolore magna
+aliqua.
+
+- Ut enim ad minim veniam
+- quis nostrud exercitation
+
+ullamco laboris nisi ut aliquip ex ea commodo consequat.
+Duis aute irure dolor in reprehenderit in voluptate velit
+
+## Baz
+
+esse cillum dolore eu fugiat nulla pariatur.
+
+<!-- BEGIN_TF_DOCS -->
+Lorem ipsum dolor sit amet, consectetur adipiscing elit
+<!-- END_TF_DOCS -->

internal/cli/testdata/writer/mode-inject-no-comment.md

@@ -0,0 +1,18 @@
+# Foo
+
+Lorem ipsum dolor sit amet, consectetur adipiscing elit.
+
+## Bar
+
+sed do eiusmod tempor incididunt ut labore et dolore magna
+aliqua.
+
+- Ut enim ad minim veniam
+- quis nostrud exercitation
+
+ullamco laboris nisi ut aliquip ex ea commodo consequat.
+Duis aute irure dolor in reprehenderit in voluptate velit
+
+## Baz
+
+esse cillum dolore eu fugiat nulla pariatur.

internal/cli/writer.go

@@ -21,7 +21,6 @@ import (
 )
 
 const (
-	errFileEmpty             = "file content is empty"
 	errTemplateEmpty         = "template is missing"
 	errBeginCommentMissing   = "begin comment is missing"
 	errEndCommentMissing     = "end comment is missing"
@@ -31,6 +30,7 @@ const (
 // stdoutWriter writes content to os.Stdout.
 type stdoutWriter struct{}
 
+// Write content to Stdout
 func (sw *stdoutWriter) Write(p []byte) (int, error) {
 	return os.Stdout.Write([]byte(string(p) + "\n"))
 }
@@ -60,11 +60,10 @@ type fileWriter struct {
 	writer io.Writer
 }
 
+// Write content to target file
 func (fw *fileWriter) Write(p []byte) (int, error) {
 	filename := fw.fullFilePath()
 
-	var buf bytes.Buffer
-
 	if fw.template == "" {
 		// template is optional for mode replace
 		if fw.mode == outputModeReplace {
@@ -73,61 +72,97 @@ func (fw *fileWriter) Write(p []byte) (int, error) {
 		return 0, errors.New(errTemplateEmpty)
 	}
 
-	tmpl := template.Must(template.New("content").Parse(fw.template))
-	if err := tmpl.ExecuteTemplate(&buf, "content", struct {
-		Content string
-	}{
-		Content: string(p),
-	}); err != nil {
+	// apply template to generated output
+	buf, err := fw.apply(p)
+	if err != nil {
 		return 0, err
 	}
 
 	// Replace the content of 'filename' with generated output,
-	// no further processing is reequired for mode 'replace'.
+	// no further processing is required for mode 'replace'.
 	if fw.mode == outputModeReplace {
 		return fw.write(filename, buf.Bytes())
 	}
 
-	content := buf.String()
-
-	f, err := os.ReadFile(filename)
+	content, err := os.ReadFile(filename)
 	if err != nil {
-		return 0, err
+		// In mode 'inject', if target file not found:
+		// create it and save the generated output into it.
+		return fw.write(filename, buf.Bytes())
+	}
+
+	if len(content) == 0 {
+		// In mode 'inject', if target file is found BUT it's empty:
+		// save the generated output into it.
+		return fw.write(filename, buf.Bytes())
+	}
+
+	return fw.inject(filename, string(content), buf.String())
+}
+
+// fullFilePath of the target file. If file is absolute path it will be
+// used as is, otherwise dir (i.e. module root folder) will be joined to
+// it.
+func (fw *fileWriter) fullFilePath() string {
+	if filepath.IsAbs(fw.file) {
+		return fw.file
+	}
+	return filepath.Join(fw.dir, fw.file)
+}
+
+// apply template to generated output
+func (fw *fileWriter) apply(p []byte) (bytes.Buffer, error) {
+	type content struct {
+		Content string
 	}
 
-	fc := string(f)
-	if fc == "" {
-		return 0, errors.New(errFileEmpty)
+	var buf bytes.Buffer
+
+	tmpl := template.Must(template.New("content").Parse(fw.template))
+	err := tmpl.ExecuteTemplate(&buf, "content", content{string(p)})
+
+	return buf, err
+}
+
+// inject generated output into file.
+func (fw *fileWriter) inject(filename string, content string, generated string) (int, error) {
+	before := strings.Index(content, fw.begin)
+	after := strings.Index(content, fw.end)
+
+	// current file content doesn't have surrounding
+	// so we're going to append the generated output
+	// to current file.
+	if before < 0 && after < 0 {
+		return fw.write(filename, []byte(content+"\n"+generated))
 	}
 
-	before := strings.Index(fc, fw.begin)
+	// begin comment is missing
 	if before < 0 {
 		return 0, errors.New(errBeginCommentMissing)
 	}
-	content = fc[:before] + content
 
-	after := strings.Index(fc, fw.end)
+	generated = content[:before] + generated
+
+	// end comment is missing
 	if after < 0 {
 		return 0, errors.New(errEndCommentMissing)
 	}
+
+	// end comment is before begin comment
 	if after < before {
 		return 0, errors.New(errEndCommentBeforeBegin)
 	}
-	content += fc[after+len(fw.end):]
 
-	return fw.write(filename, []byte(content))
+	generated += content[after+len(fw.end):]
+
+	return fw.write(filename, []byte(generated))
 }
 
+// wrtie the content to io.Writer. If no io.Writer is available,
+// it will be written to 'filename'.
 func (fw *fileWriter) write(filename string, p []byte) (int, error) {
 	if fw.writer != nil {
 		return fw.writer.Write(p)
 	}
 	return len(p), os.WriteFile(filename, p, 0644)
 }
-
-func (fw *fileWriter) fullFilePath() string {
-	if filepath.IsAbs(fw.file) {
-		return fw.file
-	}
-	return filepath.Join(fw.dir, fw.file)
-}

internal/cli/writer_test.go

@@ -80,6 +80,42 @@ func TestFileWriter(t *testing.T) {
 			wantErr:  false,
 			errMsg:   "",
 		},
+		"ModeInjectEmptyFile": {
+			file:     "empty-file.md",
+			mode:     "inject",
+			template: OutputTemplate,
+			begin:    outputBeginComment,
+			end:      outputEndComment,
+			writer:   &bytes.Buffer{},
+
+			expected: "mode-inject-empty-file",
+			wantErr:  false,
+			errMsg:   "",
+		},
+		"ModeInjectNoCommentAppend": {
+			file:     "mode-inject-no-comment.md",
+			mode:     "inject",
+			template: OutputTemplate,
+			begin:    outputBeginComment,
+			end:      outputEndComment,
+			writer:   &bytes.Buffer{},
+
+			expected: "mode-inject-no-comment",
+			wantErr:  false,
+			errMsg:   "",
+		},
+		"ModeInjectFileMissing": {
+			file:     "file-missing.md",
+			mode:     "inject",
+			template: OutputTemplate,
+			begin:    outputBeginComment,
+			end:      outputEndComment,
+			writer:   &bytes.Buffer{},
+
+			expected: "mode-inject-file-missing",
+			wantErr:  false,
+			errMsg:   "",
+		},
 		"ModeReplaceWithComment": {
 			file:     "mode-replace.md",
 			mode:     "replace",
@@ -92,6 +128,30 @@ func TestFileWriter(t *testing.T) {
 			wantErr:  false,
 			errMsg:   "",
 		},
+		"ModeReplaceWithCommentEmptyFile": {
+			file:     "mode-replace.md",
+			mode:     "replace",
+			template: OutputTemplate,
+			begin:    outputBeginComment,
+			end:      outputEndComment,
+			writer:   &bytes.Buffer{},
+
+			expected: "mode-replace-with-comment",
+			wantErr:  false,
+			errMsg:   "",
+		},
+		"ModeReplaceWithCommentFileMissing": {
+			file:     "file-missing.md",
+			mode:     "replace",
+			template: OutputTemplate,
+			begin:    outputBeginComment,
+			end:      outputEndComment,
+			writer:   &bytes.Buffer{},
+
+			expected: "mode-replace-with-comment",
+			wantErr:  false,
+			errMsg:   "",
+		},
 		"ModeReplaceWithoutComment": {
 			file:     "mode-replace.md",
 			mode:     "replace",
@@ -118,18 +178,6 @@ func TestFileWriter(t *testing.T) {
 		},
 
 		// Error writes
-		"ModeInjectNoFile": {
-			file:     "file-missing.md",
-			mode:     "inject",
-			template: OutputTemplate,
-			begin:    outputBeginComment,
-			end:      outputEndComment,
-			writer:   nil,
-
-			expected: "",
-			wantErr:  true,
-			errMsg:   "open testdata/writer/file-missing.md: no such file or directory",
-		},
 		"EmptyTemplate": {
 			file:     "not-applicable.md",
 			mode:     "inject",
@@ -142,18 +190,6 @@ func TestFileWriter(t *testing.T) {
 			wantErr:  true,
 			errMsg:   "template is missing",
 		},
-		"EmptyFile": {
-			file:     "empty-file.md",
-			mode:     "inject",
-			template: OutputTemplate,
-			begin:    outputBeginComment,
-			end:      outputEndComment,
-			writer:   nil,
-
-			expected: "",
-			wantErr:  true,
-			errMsg:   "file content is empty",
-		},
 		"BeginCommentMissing": {
 			file:     "begin-comment-missing.md",
 			mode:     "inject",