Support indented code blocks as task scripts

doc/content/task-syntax/scripts.md

@@ -37,6 +37,20 @@ echo "Hello ертөнц!"
 #+end_src
 ```
 
+## Indented code blocks
+
+A script can also be written as an indented code block, using four spaces or a tab
+instead of a ``` fence. This is handy when the surrounding document already uses
+fenced blocks for something else.
+
+````markdown
+## Tasks
+### Task1
+
+    echo "Hello 世界!"
+    echo "Hello العالمية!"
+````
+
 ## Shebangs
 
 To define an alternative interpreter such as python, then include a shebang, similar to the unix style.

parser/parsemd/parsemd.go

@@ -16,6 +16,7 @@ var ErrNoTasksHeading = errors.New("no xc block found")
 const (
 	trimValues           = "_*` "
 	codeBlockStarter     = "```"
+	indentedCodeIndent   = "    "
 	defaultHeading       = "tasks"
 	headingMarkerComment = "<!-- xc-heading -->"
 )
@@ -244,6 +245,42 @@ func (p *parser) parseCodeBlock() error {
 	return nil
 }
 
+func isIndentedCode(line string) bool {
+	return strings.HasPrefix(line, indentedCodeIndent) || strings.HasPrefix(line, "\t")
+}
+
+func trimCodeIndent(line string) string {
+	if strings.HasPrefix(line, "\t") {
+		return line[1:]
+	}
+	return strings.TrimPrefix(line, indentedCodeIndent)
+}
+
+// parseIndentedCodeBlock handles a script written as an indented code block,
+// where each line is indented with four spaces or a tab instead of being
+// wrapped in a ``` fence. A blank line does not end the block if more indented
+// code follows it, so chunks separated by a blank line are treated as one
+// script, the same way a fenced block ignores blank lines.
+func (p *parser) parseIndentedCodeBlock() error {
+	if !isIndentedCode(p.currentLine) {
+		return nil
+	}
+	if len(p.currTask.Script) > 0 {
+		return fmt.Errorf("command block already exists for task %s", p.currTask.Name)
+	}
+	for {
+		if isIndentedCode(p.currentLine) {
+			p.currTask.Script += trimCodeIndent(p.currentLine) + "\n"
+		} else if strings.TrimSpace(p.currentLine) != "" {
+			break
+		}
+		if !p.scan() {
+			break
+		}
+	}
+	return nil
+}
+
 func (p *parser) findTaskHeading() (heading string, done bool, err error) {
 	for {
 		tok, level, text, markerFound := p.parseHeading(true)
@@ -283,6 +320,9 @@ func (p *parser) parseTaskBody() (bool, error) {
 		if err != nil {
 			return false, err
 		}
+		if err = p.parseIndentedCodeBlock(); err != nil {
+			return false, err
+		}
 		tok, level, _, _ := p.parseHeading(false)
 		if tok && level <= p.rootHeadingLevel {
 			return false, nil

parser/parsemd/parsemd_test.go

@@ -24,6 +24,9 @@ var tillEOF string
 //go:embed testdata/notasks.md
 var e string
 
+//go:embed testdata/indented.md
+var indented string
+
 func assertTask(t *testing.T, expected, actual models.Task) {
 	t.Helper()
 	if expected.Name != actual.Name {
@@ -282,6 +285,61 @@ some code
 	}
 }
 
+func TestParseIndentedScripts(t *testing.T) {
+	p, err := NewParser(strings.NewReader(indented), nil)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	result, err := p.Parse()
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	expected := models.Tasks{
+		{Name: "list", Description: []string{"Lists files"}, Script: "ls\n"},
+		{
+			Name:        "greet",
+			Description: []string{"Print a message"},
+			Script:      "echo \"Hello, world!\"\necho \"Hello, world2!\"\n",
+		},
+	}
+	if len(result) != len(expected) {
+		t.Fatalf("want %d tasks got %d", len(expected), len(result))
+	}
+	for i, exp := range expected {
+		assertTask(t, exp, result[i])
+	}
+}
+
+func TestIndentedBlockSeparatedByBlankLine(t *testing.T) {
+	p, _ := NewParser(strings.NewReader(`
+# Tasks
+## a task
+    echo one
+
+    echo two
+`), nil)
+	_, err := p.parseTask()
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := "echo one\necho two\n"
+	if p.currTask.Script != want {
+		t.Fatalf("script want=%q got=%q", want, p.currTask.Script)
+	}
+}
+
+func TestIndentedBlockAfterFencedBlock(t *testing.T) {
+	var p parser
+	p.scanner = bufio.NewScanner(strings.NewReader("    echo hi"))
+	p.scan()
+	p.scan()
+	p.currTask.Script = "an existing script"
+	err := p.parseIndentedCodeBlock()
+	if err == nil {
+		t.Fatal("expected error got nil")
+	}
+}
+
 func TestMultipleCodeBlocks(t *testing.T) {
 	var p parser
 	p.scanner = bufio.NewScanner(strings.NewReader("```\ncode\n```"))

parser/parsemd/testdata/indented.md

@@ -0,0 +1,16 @@
+# My readme
+
+## Tasks
+
+### list
+
+Lists files
+
+    ls
+
+### greet
+
+Print a message
+
+	echo "Hello, world!"
+	echo "Hello, world2!"