Check for const declaration in for statement init

src/parser/__tests__/disallowed-syntax.ts

@@ -112,6 +112,37 @@ test('Cannot leave blank expressions in for loop - verbose', () => {
           `)
 })
 
+test('Cannot use const declaration in for loop init', () => {
+  return expectParsedError(
+    stripIndent`
+    let b = 1;
+    for (const a = 4; b < 10; b = b + 1) {
+      break;
+    }
+  `,
+    { chapter: Chapter.LIBRARY_PARSER }
+  ).toMatchInlineSnapshot(
+    `"Line 2: Const declaration in init part of for statement is not allowed."`
+  )
+})
+
+test('Cannot use const declaration in for loop init - verbose', () => {
+  return expectParsedError(
+    stripIndent`
+    "enable verbose";
+    let b = 1;
+    for (const a = 4; b < 10; b = b + 1) {
+      break;
+    }
+  `,
+    { chapter: Chapter.LIBRARY_PARSER }
+  ).toMatchInlineSnapshot(`
+            "Line 3, Column 0: Const declaration in init part of for statement is not allowed.
+            The init part of this statement cannot contain a const declaration, use a let declaration instead.
+            "
+          `)
+})
+
 test('Cannot leave while loop predicate blank', () => {
   return expectParsedError(
     stripIndent`

src/parser/source/rules/index.ts

@@ -4,6 +4,7 @@ import bracesAroundFor from './bracesAroundFor'
 import bracesAroundIfElse from './bracesAroundIfElse'
 import bracesAroundWhile from './bracesAroundWhile'
 import forStatementMustHaveAllParts from './forStatementMustHaveAllParts'
+import { noConstDeclarationInForLoopInit } from './noConstDeclarationInForLoopInit'
 import noDeclareMutable from './noDeclareMutable'
 import noDotAbbreviation from './noDotAbbreviation'
 import noEval from './noEval'
@@ -30,6 +31,7 @@ const rules: Rule<Node>[] = [
   bracesAroundIfElse,
   bracesAroundWhile,
   forStatementMustHaveAllParts,
+  noConstDeclarationInForLoopInit,
   noDeclareMutable,
   noDotAbbreviation,
   noExportNamedDeclarationWithDefault,

src/parser/source/rules/noConstDeclarationInForLoopInit.ts

@@ -0,0 +1,30 @@
+import type { ForStatement } from 'estree'
+import type { Rule } from '../../types'
+import { stripIndent } from '../../../utils/formatters'
+import { RuleError } from '../../errors'
+
+export class NoConstDeclarationInForLoopInit extends RuleError<ForStatement> {
+  public explain(): string {
+    return 'Const declaration in init part of for statement is not allowed.'
+  }
+  public elaborate(): string {
+    return stripIndent`
+      The init part of this statement cannot contain a const declaration, use a let declaration instead.
+    `
+  }
+}
+const noConstDeclarationInForLoopInit: Rule<ForStatement> = {
+  name: 'no-const-declaration-in-for-loop-init',
+
+  checkers: {
+    ForStatement(node) {
+      if (node.init && node.init.type === 'VariableDeclaration' && node.init.kind === 'const') {
+        return [new NoConstDeclarationInForLoopInit(node)]
+      }
+
+      return []
+    }
+  }
+}
+
+export { noConstDeclarationInForLoopInit }