feat(sequence): actor declarations

mermaid's `actor` keyword declares a participant drawn as a stick figure;
in ASCII both render as the same labelled box, so actor parses exactly like
participant (aliases, spaces in names, case-insensitive keyword, mixing
with participant declarations — mirrors mermaid's apa12/apa13 spec cases).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: cgreeno

cmd/testdata/sequence-ascii/actor_alias.txt

@@ -0,0 +1,16 @@
+sequenceDiagram
+    actor A as Alice
+    actor B as Bob
+    A->>B: Hello Bob, how are you?
+    B-->>A: I am good thanks!
+---
++-------+     +-----+
+| Alice |     | Bob |
++---+---+     +--+--+
+    |            |
+    | Hello Bob, how are you?
+    +----------->|
+    |            |
+    | I am good thanks!
+    |<...........+
+    |            |

cmd/testdata/sequence-ascii/actor_participant_mix.txt

@@ -0,0 +1,16 @@
+sequenceDiagram
+    actor Alice as Alice2
+    participant John as John2
+    Alice->>John: Hi John
+    John->>Mandy: Hi Mandy
+---
++--------+     +-------+     +-------+
+| Alice2 |     | John2 |     | Mandy |
++----+---+     +---+---+     +---+---+
+     |             |             |
+     | Hi John     |             |
+     +------------>|             |
+     |             |             |
+     |             | Hi Mandy    |
+     |             +------------>|
+     |             |             |

cmd/testdata/sequence/actor_alias.txt

@@ -0,0 +1,16 @@
+sequenceDiagram
+    actor A as Alice
+    actor B as Bob
+    A->>B: Hello Bob, how are you?
+    B-->>A: I am good thanks!
+---
+┌───────┐     ┌─────┐
+│ Alice │     │ Bob │
+└───┬───┘     └──┬──┘
+    │            │
+    │ Hello Bob, how are you?
+    ├───────────►│
+    │            │
+    │ I am good thanks!
+    │◄┈┈┈┈┈┈┈┈┈┈┈┤
+    │            │

cmd/testdata/sequence/actor_participant_mix.txt

@@ -0,0 +1,16 @@
+sequenceDiagram
+    actor Alice as Alice2
+    participant John as John2
+    Alice->>John: Hi John
+    John->>Mandy: Hi Mandy
+---
+┌────────┐     ┌───────┐     ┌───────┐
+│ Alice2 │     │ John2 │     │ Mandy │
+└────┬───┘     └───┬───┘     └───┬───┘
+     │             │             │
+     │ Hi John     │             │
+     ├────────────►│             │
+     │             │             │
+     │             │ Hi Mandy    │
+     │             ├────────────►│
+     │             │             │

pkg/sequence/actor_test.go

@@ -0,0 +1,78 @@
+package sequence
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/AlexanderGrooff/mermaid-ascii/pkg/diagram"
+)
+
+// TestActorDeclarations mirrors mermaid's actor cases (sequenceDiagram.spec.js
+// apa13): `actor` declares a participant, with or without an `as` alias.
+// mermaid draws actors as stick figures; ASCII renders the same labelled box.
+func TestActorDeclarations(t *testing.T) {
+	tests := []struct {
+		name      string
+		input     string
+		wantID    string
+		wantLabel string
+	}{
+		{"actor with alias", "sequenceDiagram\nactor A as Alice\nactor B as Bob\nA->B: Hello Bob, how are you?\nB-->A: I am good thanks!", "A", "Alice"},
+		{"actor without alias", "sequenceDiagram\nactor Alice\nAlice->>Alice: Hi", "Alice", "Alice"},
+		{"uppercase AS", "sequenceDiagram\nactor A AS Database Server\nA->>A: q", "A", "Database Server"},
+		{"case-insensitive keyword", "sequenceDiagram\nActor A as Alice\nA->>A: hi", "A", "Alice"},
+		{"actor name with spaces", "sequenceDiagram\nactor cron job as Cron\ncron job->>cron job: tick", "cron job", "Cron"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			d, err := Parse(tt.input)
+			if err != nil {
+				t.Fatalf("unexpected error: %v", err)
+			}
+			if len(d.Participants) == 0 {
+				t.Fatal("expected at least one participant")
+			}
+			p := d.Participants[0]
+			if p.ID != tt.wantID || p.Label != tt.wantLabel {
+				t.Errorf("got %q/%q, want %q/%q", p.ID, p.Label, tt.wantID, tt.wantLabel)
+			}
+			output, err := Render(d, diagram.DefaultConfig())
+			if err != nil {
+				t.Fatalf("render error: %v", err)
+			}
+			if !strings.Contains(output, tt.wantLabel) {
+				t.Errorf("output should contain label %q:\n%s", tt.wantLabel, output)
+			}
+		})
+	}
+}
+
+// TestActorParticipantMix mirrors mermaid's apa12: actors and participants
+// coexist, keep declaration order, and undeclared names in messages are still
+// auto-created after them.
+func TestActorParticipantMix(t *testing.T) {
+	d, err := Parse("sequenceDiagram\nactor Alice as Alice2\nactor Bob\nparticipant John as John2\nparticipant Mandy\nAlice->>Bob: Hi Bob\nBob->>Alice: Hi Alice\nAlice->>John: Hi John\nJohn->>Mandy: Hi Mandy\nMandy ->>Joan: Hi Joan")
+	if err != nil {
+		t.Fatal(err)
+	}
+	wantOrder := []struct{ id, label string }{
+		{"Alice", "Alice2"}, {"Bob", "Bob"}, {"John", "John2"}, {"Mandy", "Mandy"}, {"Joan", "Joan"},
+	}
+	if len(d.Participants) != len(wantOrder) {
+		t.Fatalf("want %d participants, got %d", len(wantOrder), len(d.Participants))
+	}
+	for i, w := range wantOrder {
+		if p := d.Participants[i]; p.ID != w.id || p.Label != w.label {
+			t.Errorf("participant %d = %q/%q, want %q/%q", i, p.ID, p.Label, w.id, w.label)
+		}
+	}
+}
+
+// TestActorDuplicateRejected: redeclaring a name (whether via actor or
+// participant) is a duplicate, as for participant+participant.
+func TestActorDuplicateRejected(t *testing.T) {
+	if _, err := Parse("sequenceDiagram\nactor A as Alice\nparticipant A as Al\nA->>A: hi"); err == nil {
+		t.Error("expected duplicate participant error")
+	}
+}

pkg/sequence/parser.go

@@ -15,11 +15,12 @@ const (
 )
 
 var (
-	// participantRegex matches participant declarations: participant [rest].
-	// The rest ([ID] [as Label]) is split by parseParticipant, because IDs may
-	// contain spaces (mermaid's ID lexer state allows them: "participant cron
-	// job as Cron").
-	participantRegex = regexp.MustCompile(`(?i)^\s*participant\s+(.+)$`)
+	// participantRegex matches participant declarations: participant [rest] or
+	// actor [rest]. mermaid renders an actor as a stick figure; in ASCII both
+	// forms draw the same labelled box. The rest ([ID] [as Label]) is split by
+	// parseParticipant, because IDs may contain spaces (mermaid's ID lexer
+	// state allows them: "participant cron job as Cron").
+	participantRegex = regexp.MustCompile(`(?i)^\s*(?:participant|actor)\s+(.+)$`)
 
 	// participantAsRegex splits "ID as Label" at the FIRST " as ", matching
 	// mermaid's lexer for whitespace-free IDs. For IDs containing spaces this

pkg/sequence/renderer_test.go

@@ -40,6 +40,8 @@ func TestSequenceDiagramRendering(t *testing.T) {
 		"participant_names_spaces.txt",
 		"participant_names_dashes.txt",
 		"participant_names_alias_equals.txt",
+		"actor_alias.txt",
+		"actor_participant_mix.txt",
 		"central_connections.txt",
 		"central_connection_self.txt",
 		"cross_arrows.txt",
@@ -134,6 +136,8 @@ func TestSequenceDiagramRendering_ASCIISmokeTest(t *testing.T) {
 		"participant_names_spaces.txt",
 		"participant_names_dashes.txt",
 		"participant_names_alias_equals.txt",
+		"actor_alias.txt",
+		"actor_participant_mix.txt",
 		"central_connections.txt",
 		"central_connection_self.txt",
 		"cross_arrows.txt",