d2parser: Add not ampersand support

See #1567

d2ast/d2ast.go

@@ -613,6 +613,9 @@ type Key struct {
 	// Indicates this MapKey is a filter selector.
 	Ampersand bool `json:"ampersand,omitempty"`
 
+	// Indicates this MapKey is a not filter selector.
+	NotAmpersand bool `json:"not_ampersand,omitempty"`
+
 	// At least one of Key and Edges will be set but all four can also be set.
 	// The following are all valid MapKeys:
 	// Key:

d2parser/parse.go

@@ -660,16 +660,27 @@ func (p *parser) parseMapKey() (mk *d2ast.Key) {
 		}
 	}()
 
-	// Check for ampersand/@.
+	// Check for not ampersand/@.
 	r, eof := p.peek()
 	if eof {
 		return mk
 	}
-	if r != '&' {
-		p.rewind()
-	} else {
+	if r == '!' {
+		r, eof := p.peek()
+		if eof {
+			return mk
+		}
+		if r == '&' {
+			p.commit()
+			mk.NotAmpersand = true
+		} else {
+			p.rewind()
+		}
+	} else if r == '&' {
 		p.commit()
 		mk.Ampersand = true
+	} else {
+		p.rewind()
 	}
 
 	r, eof = p.peek()

d2parser/parse_test.go

@@ -380,6 +380,18 @@ b-
 c-
 `,
 		},
+		{
+			name: "not-amper",
+			text: `
+&k: amper
+!&k: not amper
+`,
+			assert: func(t testing.TB, ast *d2ast.Map, err error) {
+				assert.Success(t, err)
+				assert.True(t, ast.Nodes[0].MapKey.Ampersand)
+				assert.True(t, ast.Nodes[1].MapKey.NotAmpersand)
+			},
+		},
 		{
 			name: "whitespace_range",
 			text: ` a -> b -> c `,