Fix parser failure on empty task content (#175)

* Initial plan

* Fix task parsing error for empty content and improve error messages

- Handle empty/whitespace-only task content gracefully in ParseTask
- Add file path to "failed to parse task content" error message
- Add unit tests for newline-only and whitespace-only inputs
- Add integration tests for tasks with empty content

Co-authored-by: alexec <1142830+alexec@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: alexec <1142830+alexec@users.noreply.github.com>

Author: Copilot

integration_test.go

@@ -1632,3 +1632,73 @@ This is a rule from a local directory without protocol.
 		}
 	}
 }
+
+// TestTaskWithEmptyContent verifies that tasks with only frontmatter
+// and empty or whitespace-only content are handled gracefully.
+func TestTaskWithEmptyContent(t *testing.T) {
+	tests := []struct {
+		name        string
+		taskName    string
+		taskContent string
+	}{
+		{
+			name:     "empty content",
+			taskName: "empty-task",
+			taskContent: `---
+task_name: empty-task
+---
+`,
+		},
+		{
+			name:     "single newline",
+			taskName: "newline-task",
+			taskContent: `---
+task_name: newline-task
+---
+
+`,
+		},
+		{
+			name:     "multiple newlines",
+			taskName: "newlines-task",
+			taskContent: `---
+task_name: newlines-task
+---
+
+
+`,
+		},
+		{
+			name:     "whitespace only",
+			taskName: "whitespace-task",
+			taskContent: `---
+task_name: whitespace-task
+---
+   
+	
+`,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			dirs := setupTestDirs(t)
+
+			// Create task file with empty or whitespace content
+			// Use the task name in the filename
+			taskFile := filepath.Join(dirs.tasksDir, tt.taskName+".md")
+			if err := os.WriteFile(taskFile, []byte(tt.taskContent), 0o644); err != nil {
+				t.Fatalf("failed to write task file: %v", err)
+			}
+
+			// Run the program - should not error
+			output := runTool(t, "-C", dirs.tmpDir, tt.taskName)
+
+			// The output should contain the frontmatter but not fail
+			// (exact output format may vary, but it should succeed)
+			if output == "" {
+				t.Errorf("expected some output, got empty string")
+			}
+		})
+	}
+}

pkg/codingcontext/context.go

@@ -152,7 +152,7 @@ func (cc *Context) findTask(taskName string) error {
 		// Parse the task content (including user_prompt) to separate text blocks from slash commands
 		task, err := taskparser.ParseTask(taskContent)
 		if err != nil {
-			return fmt.Errorf("failed to parse task content: %w", err)
+			return fmt.Errorf("failed to parse task content in file %s: %w", path, err)
 		}
 
 		// Build the final content by processing each block

pkg/codingcontext/taskparser/taskparser.go

@@ -110,6 +110,12 @@ import (
 //	task, _ := ParseTask("Introduction text\n/fix-bug 123\nSome text after")
 //	// len(task) == 3 (text, command, text)
 func ParseTask(text string) (Task, error) {
+	// Handle empty or whitespace-only content gracefully
+	// TrimSpace returns empty string for whitespace-only input
+	if strings.TrimSpace(text) == "" {
+		return Task{}, nil
+	}
+
 	input, err := parser().ParseString("", text)
 	if err != nil {
 		return nil, err

pkg/codingcontext/taskparser/taskparser_test.go

@@ -22,6 +22,36 @@ func TestParseTask(t *testing.T) {
 				}
 			},
 		},
+		{
+			name:    "single newline",
+			input:   "\n",
+			wantErr: false,
+			check: func(t *testing.T, task Task) {
+				if len(task) != 0 {
+					t.Errorf("expected empty task, got %d blocks", len(task))
+				}
+			},
+		},
+		{
+			name:    "multiple newlines",
+			input:   "\n\n\n",
+			wantErr: false,
+			check: func(t *testing.T, task Task) {
+				if len(task) != 0 {
+					t.Errorf("expected empty task, got %d blocks", len(task))
+				}
+			},
+		},
+		{
+			name:    "whitespace only",
+			input:   "   \t  \n  \n",
+			wantErr: false,
+			check: func(t *testing.T, task Task) {
+				if len(task) != 0 {
+					t.Errorf("expected empty task, got %d blocks", len(task))
+				}
+			},
+		},
 		{
 			name:    "simple text block",
 			input:   "This is a simple text block.",