fix: Improve error when parsing a non-string value (fixes #459)

Author: eemeli

docs/04_documents.md

@@ -40,6 +40,14 @@ doc.contents
 //   range: [ 0, 180, 180 ] }
 ```
 
+These functions should never throw,
+provided that `str` is a string and the `options` are valid.
+Errors and warnings are included in the documents' `errors` and `warnings` arrays.
+In particular, if `errors` is not empty
+it's likely that the document's parsed `contents` are not entirely correct.
+
+The `contents` of a parsed document will always consist of `Scalar`, `Map`, `Seq` or `null` values.
+
 #### `parseDocument(str, options = {}): Document`
 
 Parses a single `Document` from the input `str`; used internally by `parse`.
@@ -56,10 +64,6 @@ See [Options](#options) for more information on the second parameter.
 
 <br/>
 
-These functions should never throw; errors and warnings are included in the documents' `errors` and `warnings` arrays. In particular, if `errors` is not empty it's likely that the document's parsed `contents` are not entirely correct.
-
-The `contents` of a parsed document will always consist of `Scalar`, `Map`, `Seq` or `null` values.
-
 ## Creating Documents
 
 #### `new Document(value, replacer?, options = {})`

src/parse/lexer.ts

@@ -174,6 +174,7 @@ export class Lexer {
    */
   *lex(source: string, incomplete = false) {
     if (source) {
+      if (typeof source !== 'string') throw TypeError('source is not a string')
       this.buffer = this.buffer ? this.buffer + source : source
       this.lineEndPos = null
     }

tests/doc/parse.ts

@@ -154,6 +154,15 @@ aliases:
   })
 })
 
+test('buffer as source (eemeli/yaml#459)', () => {
+  const buffer = readFileSync(
+    resolve(__dirname, '../artifacts/prettier-circleci-config.yml')
+  )
+  expect(() => YAML.parseDocument(buffer as any)).toThrow(
+    'source is not a string'
+  )
+})
+
 describe('eemeli/yaml#19', () => {
   test('map', () => {
     const src = 'a:\n  # 123'