Preserve previous context when processing type-scoped contexts.

Author: dlongley

lib/compact.js

@@ -143,8 +143,8 @@ api.compact = ({
 
     const rval = {};
 
-    // revert type scoped terms
-    activeCtx = activeCtx.revertTypeScopedTerms();
+    // revert type scoped context
+    activeCtx = activeCtx.revertTypeScopedContext();
 
     if(options.link && '@id' in element) {
       // store linked element

lib/context.js

@@ -66,6 +66,23 @@ api.process = ({
     return activeCtx;
   }
 
+  // track the previous context
+  const previousContext = activeCtx;
+
+  // if context is property scoped and there's a previous context, amend it,
+  // not the current one
+  if(isPropertyTermScopedContext && activeCtx.previousContext) {
+    // TODO: consider optimizing to a shallow copy
+    activeCtx = activeCtx.clone();
+    activeCtx.previousContext = api.process({
+      activeCtx: activeCtx.previousContext,
+      localCtx: ctxs,
+      options,
+      isPropertyTermScopedContext
+    });
+    return activeCtx;
+  }
+
   // process each context in order, update active context
   // on each iteration to ensure proper caching
   let rval = activeCtx;
@@ -75,15 +92,6 @@ api.process = ({
     // update active context to one computed from last iteration
     activeCtx = rval;
 
-    // get context from cache if available
-    if(api.cache) {
-      const cached = api.cache.get(activeCtx, ctx);
-      if(cached) {
-        rval = activeCtx = cached;
-        continue;
-      }
-    }
-
     // reset to initial context
     if(ctx === null) {
       // We can't nullify if there are protected terms and we're
@@ -102,7 +110,7 @@ api.process = ({
           console.warn('WARNING: invalid context nullification');
           const oldActiveCtx = activeCtx;
           // copy all protected term definitions to fresh initial context
-          rval = activeCtx = api.getInitialContext(options);
+          rval = activeCtx = api.getInitialContext(options).clone();
           for(const [term, _protected] of
             Object.entries(oldActiveCtx.protected)) {
             if(_protected) {
@@ -124,10 +132,23 @@ api.process = ({
           'jsonld.SyntaxError',
           {code: 'invalid protected mode', context: localCtx, protectedMode});
       }
-      rval = activeCtx = api.getInitialContext(options);
+      rval = activeCtx = api.getInitialContext(options).clone();
+      // if context is type-scoped, ensure previous context has been set
+      if(isTypeScopedContext) {
+        rval.previousContext = previousContext.clone();
+      }
       continue;
     }
 
+    // get context from cache if available
+    if(api.cache) {
+      const cached = api.cache.get(activeCtx, ctx);
+      if(cached) {
+        rval = activeCtx = cached;
+        continue;
+      }
+    }
+
     // dereference @context key if present
     if(_isObject(ctx) && '@context' in ctx) {
       ctx = ctx['@context'];
@@ -140,6 +161,9 @@ api.process = ({
         'jsonld.SyntaxError', {code: 'invalid local context', context: ctx});
     }
 
+    // TODO: there is likely a `preivousContext` cloning optimization that
+    // could be applied here (no need to copy it under certain conditions)
+
     // clone context before updating it
     rval = rval.clone();
 
@@ -239,7 +263,12 @@ api.process = ({
     for(const key in ctx) {
       api.createTermDefinition(
         rval, ctx, key, defined, options,
-        isPropertyTermScopedContext, isTypeScopedContext);
+        isPropertyTermScopedContext);
+    }
+
+    // if context is type-scoped, ensure previous context has been set
+    if(isTypeScopedContext && !rval.previousContext) {
+      rval.previousContext = previousContext.clone();
     }
 
     // cache result
@@ -248,6 +277,11 @@ api.process = ({
     }
   }
 
+  // if context is type-scoped, ensure previous context has been set
+  if(isTypeScopedContext && !rval.previousContext) {
+    rval.previousContext = previousContext.clone();
+  }
+
   return rval;
 };
 
@@ -265,13 +299,10 @@ api.process = ({
  *   signal a warning.
  * @param isPropertyTermScopedContext `true` if `localCtx` is a scoped context
  *   from a property term.
- * @param isTypeScopedContext `true` if `localCtx` is a scoped context
- *   from a type.
  */
 api.createTermDefinition = (
   activeCtx, localCtx, term, defined, options,
-  isPropertyTermScopedContext = false,
-  isTypeScopedContext = false) => {
+  isPropertyTermScopedContext = false) => {
   if(defined.has(term)) {
     // term already defined
     if(defined.get(term)) {
@@ -301,10 +332,11 @@ api.createTermDefinition = (
       {code: 'invalid term definition', context: localCtx});
   }
 
+  // keep reference to previous mapping for potential `@protected` check
+  const previousMapping = activeCtx.mappings.get(term);
+
   // remove old mapping
-  let previousMapping = null;
   if(activeCtx.mappings.has(term)) {
-    previousMapping = activeCtx.mappings.get(term);
     activeCtx.mappings.delete(term);
   }
 
@@ -339,11 +371,6 @@ api.createTermDefinition = (
   // create new mapping
   const mapping = {};
   activeCtx.mappings.set(term, mapping);
-  if(isTypeScopedContext) {
-    activeCtx.hasTypeScopedTerms = true;
-    mapping.isTypeScopedTerm = true;
-    mapping.previousMapping = previousMapping;
-  }
   mapping.reverse = false;
 
   // make sure term definition only has expected keywords
@@ -785,7 +812,7 @@ api.getInitialContext = options => {
     inverse: null,
     getInverse: _createInverseContext,
     clone: _cloneActiveContext,
-    revertTypeScopedTerms: _revertTypeScopedTerms,
+    revertTypeScopedContext: _revertTypeScopedContext,
     protected: {}
   };
   // TODO: consider using LRU cache instead
@@ -961,7 +988,10 @@ api.getInitialContext = options => {
     child.inverse = null;
     child.getInverse = this.getInverse;
     child.protected = util.clone(this.protected);
-    child.revertTypeScopedTerms = this.revertTypeScopedTerms;
+    if(this.previousContext) {
+      child.previousContext = this.previousContext.clone();
+    }
+    child.revertTypeScopedContext = this.revertTypeScopedContext;
     if('@language' in this) {
       child['@language'] = this['@language'];
     }
@@ -972,35 +1002,14 @@ api.getInitialContext = options => {
   }
 
   /**
-   * Reverts any type-scoped terms in this active context to their previous
-   * mappings.
+   * Reverts any type-scoped context in this active context to the previous
+   * context.
    */
-  function _revertTypeScopedTerms() {
-    // optimization: no type-scoped terms to remove, reuse active context
-    if(!this.hasTypeScopedTerms) {
+  function _revertTypeScopedContext() {
+    if(!this.previousContext) {
       return this;
     }
-    // create clone without type scoped terms
-    const child = this.clone();
-    const entries = child.mappings.entries();
-    for(const [term, mapping] of entries) {
-      if(mapping.isTypeScopedTerm) {
-        if(mapping.previousMapping) {
-          child.mappings.set(term, mapping.previousMapping);
-          if(mapping.previousMapping.protected) {
-            child.protected[term] = true;
-          } else {
-            delete child.protected[term];
-          }
-        } else {
-          child.mappings.delete(term);
-          if(child.protected[term]) {
-            delete child.protected[term];
-          }
-        }
-      }
-    }
-    return child;
+    return this.previousContext.clone();
   }
 };
 

lib/expand.js

@@ -153,8 +153,8 @@ api.expand = ({
   // recursively expand object:
 
   if(!insideIndex) {
-    // revert type scoped terms
-    activeCtx = activeCtx.revertTypeScopedTerms();
+    // revert type scoped context
+    activeCtx = activeCtx.revertTypeScopedContext();
   }
 
   // if element has a context, process it
@@ -613,8 +613,8 @@ function _expandObject({
     } else if(container.includes('@type') && _isObject(value)) {
       // handle type container (skip if value is not an object)
       expandedValue = _expandIndexMap({
-        // since container is `@type`, revert type scoped terms when expanding
-        activeCtx: termCtx.revertTypeScopedTerms(),
+        // since container is `@type`, revert type scoped context when expanding
+        activeCtx: termCtx.revertTypeScopedContext(),
         options,
         activeProperty: key,
         value,