fix(context): refuse an inline @context entry as a keyword redefinition

lib/ContextResolver.js

@@ -29,10 +29,16 @@ module.exports = class ContextResolver {
   }
 
   async resolve({
-    activeCtx, context, documentLoader, base, cycles = new Set()
+    activeCtx, context, documentLoader, base, cycles = new Set(),
+    isRemote = false
   }) {
-    // process `@context`
-    if(context && _isObject(context) && context['@context']) {
+    // process `@context`; only a dereferenced remote document is unwrapped
+    // (JSON-LD 1.1 API 4.1.2 step 5.2.5). An inline context map that carries
+    // an `@context` entry is a context definition: its `@context` key
+    // reaches Create Term Definition (step 5.13 -> 4.2.2 step 5) and is
+    // refused as a keyword redefinition, not silently unwrapped.
+    if(isRemote && context && _isObject(context) &&
+      context['@context']) {
       context = context['@context'];
     }
 
@@ -123,7 +129,7 @@ module.exports = class ContextResolver {
 
     // resolve, cache, and return context
     const resolved = await this.resolve(
-      {activeCtx, context, documentLoader, base, cycles});
+      {activeCtx, context, documentLoader, base, cycles, isRemote: true});
     this._cacheResolvedContext({key: url, resolved, tag: remoteDoc.tag});
     return resolved;
   }

lib/context.js

@@ -145,10 +145,12 @@ api.process = async ({
       continue;
     }
 
-    // dereference @context key if present
-    if(_isObject(ctx) && '@context' in ctx) {
-      ctx = ctx['@context'];
-    }
+    // Note: no `@context` dereference happens here. Only a dereferenced
+    // remote document is unwrapped (JSON-LD 1.1 API 4.1.2 step 5.2.5), and
+    // ContextResolver does that for remote contexts; an inline context map
+    // that carries an `@context` entry is a context definition, whose
+    // `@context` key reaches Create Term Definition (step 5.13 -> 4.2.2
+    // step 5) and is refused as a keyword redefinition instead.
 
     // context must be an object by now, all URLs retrieved before this call
     if(!_isObject(ctx)) {

tests/misc.js

@@ -8,6 +8,71 @@ const assert = require('assert');
 
 // TODO: need more tests for jsonld.link and jsonld.merge
 
+describe('inline context `@context` keyword redefinition (issue #588)', () => {
+  const REMOTE = 'https://example.org/remote-context.jsonld';
+  const held = {
+    [REMOTE]: {'@context': {name: 'http://example.org/name'}}
+  };
+  const documentLoader = async url => {
+    if(!(url in held)) {
+      throw new Error(`not held: ${url}`);
+    }
+    return {contextUrl: null, documentUrl: url, document: held[url]};
+  };
+
+  it('refuses an inline context map that carries an \'@context\' entry', async () => {
+    const doc = {
+      '@context': {'@context': {name: 'http://example.org/name'}},
+      name: 'x'
+    };
+    let error;
+    try {
+      await jsonld.expand(doc, {documentLoader});
+    } catch(e) {
+      error = e;
+    }
+    assert(error, 'expected a keyword redefinition error');
+    assert.equal(error.details.code, 'keyword redefinition');
+  });
+
+  it('refuses the same map as an element of a context array', async () => {
+    const doc = {
+      '@context': [{'@context': {name: 'http://example.org/name'}}],
+      name: 'x'
+    };
+    let error;
+    try {
+      await jsonld.expand(doc, {documentLoader});
+    } catch(e) {
+      error = e;
+    }
+    assert(error, 'expected a keyword redefinition error');
+    assert.equal(error.details.code, 'keyword redefinition');
+  });
+
+  it('still refuses other keywords as terms of an inline context', async () => {
+    const doc = {
+      '@context': {'@id': 'http://example.org/id'},
+      name: 'x'
+    };
+    let error;
+    try {
+      await jsonld.expand(doc, {documentLoader});
+    } catch(e) {
+      error = e;
+    }
+    assert(error, 'expected a keyword redefinition error');
+    assert.equal(error.details.code, 'keyword redefinition');
+  });
+
+  it('still unwraps a dereferenced remote context (control)', async () => {
+    const doc = {'@context': REMOTE, name: 'x'};
+    const expanded = await jsonld.expand(doc, {documentLoader});
+    assert.deepEqual(expanded,
+      [{'http://example.org/name': [{'@value': 'x'}]}]);
+  });
+});
+
 describe('link tests', () => {
   const doc = {
     "@id": "ex:1",