feat(content): Expression, ExpressionMap

Signed-off-by: Lexus Drumgold <unicornware@flexdevelopment.llc>

src/content/__tests__/expression.spec-d.ts

@@ -0,0 +1,31 @@
+/**
+ * @file Type Tests - expression
+ * @module esast/content/tests/unit-d/expression
+ */
+
+import type { Identifier, LiteralMap } from '@flex-development/esast'
+import type * as TestSubject from '../expression'
+
+describe('unit-d:content/expression', () => {
+  describe('Expression', () => {
+    it('should equal ExpressionMap[keyof ExpressionMap]', () => {
+      // Arrange
+      type Expect = TestSubject.ExpressionMap[keyof TestSubject.ExpressionMap]
+
+      // Expect
+      expectTypeOf<TestSubject.Expression>().toEqualTypeOf<Expect>
+    })
+  })
+
+  describe('ExpressionMap', () => {
+    it('should extend LiteralMap', () => {
+      expectTypeOf<TestSubject.ExpressionMap>().toMatchTypeOf<LiteralMap>()
+    })
+
+    it('should match [identifier: Identifier]', () => {
+      expectTypeOf<TestSubject.ExpressionMap>()
+        .toHaveProperty('identifier')
+        .toEqualTypeOf<Identifier>
+    })
+  })
+})

src/content/expression.ts

@@ -0,0 +1,35 @@
+/**
+ * @file Content - expression
+ * @module esast/content/expression
+ */
+
+import type { Identifier, LiteralMap } from '@flex-development/esast'
+
+/**
+ * Union of registered esast nodes that can occur where an expression is
+ * expected.
+ *
+ * To register custom esast nodes, augment {@linkcode ExpressionMap}. They will
+ * be added to this union automatically.
+ */
+type Expression = ExpressionMap[keyof ExpressionMap]
+
+/**
+ * Registry of nodes that can occur where an {@linkcode Expression} is expected.
+ *
+ * This interface can be augmented to register custom node types.
+ *
+ * @example
+ *  declare module '@flex-development/docast' {
+ *    interface ExpressionMap {
+ *      customExpression: CustomExpression
+ *    }
+ *  }
+ *
+ * @extends {LiteralMap}
+ */
+interface ExpressionMap extends LiteralMap {
+  identifier: Identifier
+}
+
+export type { Expression, ExpressionMap }

src/content/index.ts

@@ -3,6 +3,7 @@
  * @module esast/content
  */
 
+export type * from './expression'
 export type * from './literal'
 export type * from './pattern'
 export type * from './primitive'