Commit 37bb02c3 authored by Erik Nordin's avatar Erik Nordin Committed by enordin@mozilla.com
Browse files

Bug 1967792 - Do not re-translate translated attributes r=translations-reviewers,gregtatum 

This patch fixes an edge case where the page itself may replace
an attribute with content that has already been translated.
This would previously cause the TranslationsDocument to translate
the text a second time, which, depending on the model, may reduce
the quality of the translation.

This is a common occurrence on Wikipedia, which will delete the
"title" attributes on `<a>` elements when moused over, and replace
them when the curor leaves.

The caching mechanism is now updated such that we will not re-translate
text that we know to be the output of a recent translation. This does
not, however, guard against the page inserting new text that happens
to be in the target language, which was not the previous result of
a translation request.

Differential Revision: https://phabricator.services.mozilla.com/D249978
parent 43f8333c

toolkit/components/translations/content/translations-document.sys.mjs

+61 −6
Original line number Diff line number Diff line
@@ -95,6 +95,23 @@ export class LRUCache { 
   */

  #textCacheMap = new Map();



  /**

   * A Set containing strings of translated plain text output.

   *

   * This cache is used to check if the text has already been translated,

   * to help avoid sending already-translated text to be translated a second time.

   *

   * Ideally, a translation model that receives source text that is already in the

   * target translation language should just pass it through, but this is not always

   * the case in practice. Depending on the model, sending already-translated text to

   * be translated again may change the translation or even produce garbage as a response.

   *

   * Best to avoid this situation altogether if we can.

   *

   * @type {Set<string>}

   */

  #textCacheSet = new Set();



  /**

   * The language pair for this cache. All cached translations will be for the given pair.

   *
@@ -189,9 +206,36 @@ export class LRUCache { 
    }

    cacheMap.set(sourceString, targetString);



    if (!isHTML) {

      if (this.#textCacheSet.has(targetString)) {

        // The Set already has this value, so we must delete it to

        // re-insert it at the most-recently-used position of the Set.

        this.#textCacheSet.delete(targetString);

      } else if (this.#textCacheSet.size === this.#cacheLimit) {

        // The Set is at capacity, so we must evict the least-recently-used value.

        const oldestKey = this.#textCacheSet.keys().next().value;

        // @ts-ignore: We can ensure that oldestKey is not undefined.

        this.#textCacheSet.delete(oldestKey);

      }

      this.#textCacheSet.add(targetString);

    }



    this.keepAlive();

  }



  /**

   * Returns true if the source text is text that has already been translated

   * into the target language, otherwise false. If so, we want to avoid sending

   * this text to be translated a second time. Depending on the model, retranslating

   * text that is already in the target language may produce garbage output.

   *

   * @param {string} sourceText

   * @returns {boolean}

   */

  isAlreadyTranslated(sourceText) {

    return this.#textCacheSet.has(sourceText);

  }



  /**

   * Returns true if the given pair matches the language pair for this cache, otherwise false.

   *
@@ -246,6 +290,7 @@ export class LRUCache { 
      this.#keepAliveTimeoutId = lazy.setTimeout(() => {

        this.#htmlCacheMap = new Map();

        this.#textCacheMap = new Map();

        this.#textCacheSet = new Set();

      }, this.#cacheExpirationMS);

    }, 0);

  }
@@ -441,6 +486,7 @@ const MUTATION_OBSERVER_OPTIONS = { 
  childList: true,

  subtree: true,

  attributes: true,

  attributeOldValue: true,

  attributeFilter: [...TRANSLATABLE_ATTRIBUTES.keys()],

};
@@ -820,18 +866,27 @@ export class TranslationsDocument { 
              // Ignore others such as the comment node.

              // https://developer.mozilla.org/en-US/docs/Web/API/CharacterData

              if (node.nodeType === Node.TEXT_NODE) {

                this.#processedContentNodes.delete(node);

                this.#markNodeContentMutated(node);

              }

            }

            break;

          }

          case "attributes": {

            if (mutation.target && mutation.attributeName) {

              this.#maybeMarkElementAttributeMutated(

                mutation.target,

                mutation.attributeName

              );

            const element = asElement(mutation.target);

            if (element && mutation.attributeName) {

              const { oldValue, attributeName } = mutation;

              const newValue = element.getAttribute(attributeName);



              if (

                // The new attribute value must have content to translate.

                newValue?.length &&

                // The new attribute value must not be exactly the same as the old value.

                oldValue !== newValue &&

                // The new attribute value must not be already-translated text.

                !this.#translationsCache.isAlreadyTranslated(newValue)

              ) {

                this.#maybeMarkElementAttributeMutated(element, attributeName);

              }

            }

            break;

          }