add lint rule to catch for-each-in (#691)

Author: michaelficarra

src/lint/collect-algorithm-diagnostics.ts

@@ -11,6 +11,7 @@ import lintAlgorithmStepNumbering from './rules/algorithm-step-numbering';
 import lintAlgorithmStepLabels from './rules/algorithm-step-labels';
 import lintEnumCasing from './rules/enum-casing';
 import lintForEachElement from './rules/for-each-element';
+import lintForEachOf from './rules/for-each-of';
 import lintStepAttributes from './rules/step-attributes';
 import lintIfElseConsistency from './rules/if-else-consistency';
 import lintAlgorithmSpelling from './rules/algorithm-spelling';
@@ -31,6 +32,7 @@ const stepRules: LineRule[] = [
   lintAlgorithmStepLabels,
   lintEnumCasing,
   lintForEachElement,
+  lintForEachOf,
   lintStepAttributes,
   lintIfElseConsistency,
   lintAlgorithmSpelling,

src/lint/rules/for-each-of.ts

@@ -0,0 +1,40 @@
+import type { Reporter } from '../algorithm-error-reporter-type';
+import type { Seq } from '../../expr-parser';
+import type { OrderedListItemNode } from 'ecmarkdown';
+import { offsetToLineAndColumn } from '../../utils';
+
+const ruleId = 'for-each-of';
+
+/*
+Checks that "For each" loops use "of", not "in".
+*/
+export default function (
+  report: Reporter,
+  step: OrderedListItemNode,
+  algorithmSource: string,
+  parsedSteps: Map<OrderedListItemNode, Seq>,
+) {
+  const stepSeq = parsedSteps.get(step);
+  if (stepSeq == null || stepSeq.items.length < 3) {
+    return;
+  }
+  const first = stepSeq.items[0];
+  if (!(first.name === 'text' && first.contents.startsWith('For each '))) {
+    return;
+  }
+  // Find the loop variable (underscore), then check the text after it
+  for (let i = 1; i < stepSeq.items.length - 1; i++) {
+    const item = stepSeq.items[i];
+    if (item.name === 'underscore') {
+      const next = stepSeq.items[i + 1];
+      if (next.name === 'text' && /^ in\b/.test(next.contents)) {
+        report({
+          ruleId,
+          ...offsetToLineAndColumn(algorithmSource, next.location.start.offset + 1),
+          message: 'expected "of" instead of "in" in "for each"',
+        });
+      }
+      break;
+    }
+  }
+}

test/lint-algorithms.ts

@@ -524,6 +524,36 @@ describe('linting algorithms', () => {
     });
   });
 
+  describe('for each of', () => {
+    const ruleId = 'for-each-of';
+    it('rejects "in" instead of "of"', async () => {
+      await assertLint(
+        positioned`
+        <emu-alg>
+          1. Let _y_ be a List.
+          1. For each String _x_ ${M}in _y_, do foo.
+        </emu-alg>`,
+        {
+          ruleId,
+          nodeType,
+          message: 'expected "of" instead of "in" in "for each"',
+        },
+      );
+    });
+
+    it('negative', async () => {
+      await assertLintFree(`
+        <emu-alg>
+          1. Let _y_ be a List.
+          1. Let _S_ be a Set.
+          1. For each String _x_ of _y_, do foo.
+          1. For each element _x_ of _y_, do foo.
+          1. For each integer _x_ such that _x_ &in; _S_, do foo.
+        </emu-alg>
+      `);
+    });
+  });
+
   describe('if/else consistency', () => {
     const ruleId = 'if-else-consistency';
     it('rejects single-line if with multiline else', async () => {