fix: skip impossible TypeScript type offset scans (#445)

Author: levivilet

src/tokenizeTypeScript.js

@@ -483,6 +483,9 @@ const addTypeOffsets = (offsets, type, typeOffset) => {
 
 const getFunctionParameterTypeOffsets = (line) => {
   const offsets = new Map()
+  if (!line.includes(':')) {
+    return offsets
+  }
   for (const match of line.matchAll(RE_FUNCTION_PARAMETER_TYPE)) {
     const type = match[1]
     const typeOffset = match.index + match[0].lastIndexOf(type)
@@ -536,6 +539,9 @@ const getArrowFunctionTypeOffsets = (line) => {
 
 const getGenericTypeArgumentOffsets = (line) => {
   const offsets = new Map()
+  if (!line.includes('<') || !line.includes(',')) {
+    return offsets
+  }
   for (const match of line.matchAll(RE_GENERIC_TYPE_ARGUMENTS)) {
     for (const argumentIndex of [1, 2]) {
       const typeArguments = match[argumentIndex]

test/offsetScans.test.js

@@ -0,0 +1,51 @@
+import assert from 'node:assert/strict'
+import { test } from 'node:test'
+import {
+  initialLineState,
+  TokenMap,
+  tokenizeLine,
+} from '../src/tokenizeTypeScript.js'
+
+const tokenize = (source) => {
+  let state = structuredClone(initialLineState)
+  const result = []
+  for (const line of source.split('\n')) {
+    state = tokenizeLine(line, state)
+    let offset = 0
+    for (let index = 0; index < state.tokens.length; index += 2) {
+      const length = state.tokens[index + 1]
+      result.push([
+        TokenMap[state.tokens[index]],
+        line.slice(offset, offset + length),
+      ])
+      offset += length
+    }
+    assert.equal(offset, line.length)
+  }
+  return result
+}
+
+test('preserves parameter and generic type classifications across scan fast paths', () => {
+  const tokens = tokenize(`const value = 1
+function first(value: number) {}
+const plain = value
+const table: Map<string, User> = new Map()
+const identity = (value: User): User => value
+/* open
+comment */
+function last(value: boolean) {}`)
+  assert.ok(
+    tokens.some(([type, text]) => type === 'TypePrimitive' && text === 'number')
+  )
+  assert.ok(
+    tokens.some(
+      ([type, text]) => type === 'TypePrimitive' && text === 'boolean'
+    )
+  )
+  assert.ok(tokens.some(([type, text]) => type === 'Type' && text === 'User'))
+  assert.ok(
+    tokens.some(
+      ([type, text]) => type === 'Comment' && text.includes('comment')
+    )
+  )
+})