Fix 'oneof' in syntax-directed operations

src/lint/utils.ts

@@ -73,7 +73,10 @@ export function rhsMatches(a: RightHandSide | OneOfList, b: RightHandSide | OneO
       }
       return symbolSpanMatches(aHead, bHead);
     }
+    case SyntaxKind.OneOfList:
+      return oneOfListMatches(a, b as OneOfList);
     default:
+      // @ts-expect-error: Callers might pass other kinds of nodes.
       throw new Error('unknown rhs type ' + a.constructor.name);
   }
 }
@@ -171,6 +174,14 @@ function argumentListMatches(a: ArgumentList, b: ArgumentList) {
   );
 }
 
+function oneOfListMatches(a: OneOfList, b: OneOfList) {
+  if (a.terminals === undefined || b.terminals === undefined) {
+    throw new Error('OneOfList must have terminals');
+  }
+  // The terminals in a must be a subset of the terminals in b.
+  return a.terminals.every(ae => b.terminals!.find(be => ae.text === be.text));
+}
+
 // this is only for use with single-file grammars
 export function getLocationInGrammarFile(file: SourceFile, pos: number) {
   const posWithoutWhitespace = skipTrivia(file.text, pos, file.text.length);

test/errors.js

@@ -1106,6 +1106,31 @@ ${M}      </pre>
       );
     });
 
+    it('unknown oneof', async () => {
+      await assertError(
+        positioned`
+        <emu-grammar type="definition">
+          Foo :: one of \`a\` \`b\` \`c\`
+        </emu-grammar>
+
+        <emu-clause id="sec-example" type="sdo">
+        <h1>Static Semantics: Example</h1>
+        <dl class='header'></dl>
+          <emu-grammar>
+            Foo :: ${M}one of \`d\` \`e\`
+          </emu-grammar>
+          <emu-alg>
+            1. Return *true*.
+          </emu-alg>
+        </emu-clause>`,
+        {
+          ruleId: 'grammar-shape',
+          nodeType: 'emu-grammar',
+          message: 'could not find definition for rhs "d e"',
+        },
+      );
+    });
+
     it('negative', async () => {
       await assertErrorFree(`
         <emu-grammar type="definition">
@@ -1167,5 +1192,49 @@ ${M}      </pre>
         },
       );
     });
+
+    it('negative: oneof', async () => {
+      await assertErrorFree(`
+        <emu-grammar type="definition">
+          Foo :: one of \`a\` \`b\` \`c\`
+        </emu-grammar>
+
+        <emu-clause id="sec-example" type="sdo">
+        <h1>Static Semantics: Example</h1>
+        <dl class='header'></dl>
+          <emu-grammar>
+            Foo :: one of \`a\` \`b\` \`c\`
+          </emu-grammar>
+          <emu-alg>
+            1. Return *true*.
+          </emu-alg>
+        </emu-clause>
+      `);
+    });
+
+    it('negative: oneof (subset)', async () => {
+      await assertErrorFree(`
+        <emu-grammar type="definition">
+          Foo :: one of \`a\` \`b\` \`c\` \`d\`
+        </emu-grammar>
+
+        <emu-clause id="sec-example" type="sdo">
+        <h1>Static Semantics: Example</h1>
+        <dl class='header'></dl>
+          <emu-grammar>
+            Foo :: one of \`a\` \`b\`
+          </emu-grammar>
+          <emu-alg>
+            1. Return *true*.
+          </emu-alg>
+          <emu-grammar>
+            Foo :: one of \`c\` \`d\`
+          </emu-grammar>
+          <emu-alg>
+            1. Return *false*.
+          </emu-alg>
+        </emu-clause>
+      `);
+    });
   });
 });