.. role:: bash(code) :language: bash .. role:: js(code) :language: javascript .. role:: python(code) :language: python ======================== Migrating Legacy Formats ======================== Migrating from legacy formats (.dtd, .properties) is different from migrating Fluent to Fluent. When migrating legacy code paths, you'll need to adjust the Fluent strings for the quirks Mozilla uses in the legacy code paths. You'll find a number of specialized functionalities here. Legacy Migration Tools ---------------------- To assist with legacy format migrations, some scripting tools are provided: - `XUL+DTD to Fluent`_ - `.properties to Fluent`_ When creating a migration, one or both of these tools may provide a good starting point for manual work by automating at least a part of the migration, including recipe generation and refactoring the calling code. .. _XUL+DTD to Fluent: https://github.com/zbraniecki/convert_xul_to_fluent .. _.properties to Fluent: https://github.com/mozilla/properties-to-ftl Basic Migration --------------- Let’s consider a basic example: one string needs to be migrated, without any further change, from a DTD file to Fluent. The legacy string is stored in :bash:`toolkit/locales/en-US/chrome/global/findbar.dtd`: .. code-block:: dtd The new Fluent string is stored in :bash:`toolkit/locales/en-US/toolkit/main-window/findbar.ftl`: .. code-block:: properties findbar-next = .tooltiptext = Find the next occurrence of the phrase This is how the migration recipe looks: .. code-block:: python # Any copyright is dedicated to the Public Domain. # http://creativecommons.org/publicdomain/zero/1.0/ from __future__ import absolute_import import fluent.syntax.ast as FTL from fluent.migrate.helpers import transforms_from def migrate(ctx): """Bug 1411707 - Migrate the findbar XBL binding to a Custom Element, part {index}.""" ctx.add_transforms( "toolkit/toolkit/main-window/findbar.ftl", "toolkit/toolkit/main-window/findbar.ftl", transforms_from( """ findbar-next = .tooltiptext = { COPY(from_path, "next.tooltip") } """, from_path="toolkit/chrome/global/findbar.dtd")) The first important thing to notice is that the migration recipe needs file paths relative to a localization repository, losing :bash:`locales/en-US/`: - :bash:`toolkit/locales/en-US/chrome/global/findbar.dtd` becomes :bash:`toolkit/chrome/global/findbar.dtd`. - :bash:`toolkit/locales/en-US/toolkit/main-window/findbar.ftl` becomes :bash:`toolkit/toolkit/main-window/findbar.ftl`. The :python:`context.add_transforms` function takes 3 arguments: - Path to the target l10n file. - Path to the reference (en-US) file. - An array of Transforms. Transforms are AST nodes which describe how legacy translations should be migrated. .. note:: For migrations of Firefox localizations, the target and reference path are the same. This isn't true for all projects that use Fluent, so both arguments are required. In this case there is only one Transform that migrates the string with ID :js:`next.tooltip` from :bash:`toolkit/chrome/global/findbar.dtd`, and injects it in the FTL fragment. The :python:`COPY` Transform allows to copy the string from an existing file as is, while :python:`from_path` is used to avoid repeating the same path multiple times, making the recipe more readable. Without :python:`from_path`, this could be written as: .. code-block:: python ctx.add_transforms( "toolkit/toolkit/main-window/findbar.ftl", "toolkit/toolkit/main-window/findbar.ftl", transforms_from( """ findbar-next = .tooltiptext = { COPY("toolkit/chrome/global/findbar.dtd", "next.tooltip") } """)) This method of writing migration recipes allows to take the original FTL strings, and simply replace the value of each message with a :python:`COPY` Transform. :python:`transforms_from` takes care of converting the FTL syntax into an array of Transforms describing how the legacy translations should be migrated. This manner of defining migrations is only suitable to simple strings where a copy operation is sufficient. For more complex use-cases which require some additional logic in Python, it’s necessary to resort to the raw AST. The example above is equivalent to the following syntax, which exposes the underlying AST structure: .. code-block:: python ctx.add_transforms( "toolkit/toolkit/main-window/findbar.ftl", "toolkit/toolkit/main-window/findbar.ftl", [ FTL.Message( id=FTL.Identifier("findbar-next"), attributes=[ FTL.Attribute( id=FTL.Identifier("tooltiptext"), value=COPY( "toolkit/chrome/global/findbar.dtd", "next.tooltip" ) ) ] ) ] ) This creates a :python:`Message`, taking the value from the legacy string :js:`findbar-next`. A message can have an array of attributes, each with an ID and a value: in this case there is only one attribute, with ID :js:`tooltiptext` and :js:`value` copied from the legacy string. Notice how both the ID of the message and the ID of the attribute are defined as an :python:`FTL.Identifier`, not simply as a string. .. tip:: It’s possible to concatenate arrays of Transforms defined manually, like in the last example, with those coming from :python:`transforms_from`, by using the :python:`+` operator. Alternatively, it’s possible to use multiple :python:`add_transforms`. The order of Transforms provided in the recipe is not relevant, the reference file is used for ordering messages. Replacing Content in Legacy Strings ----------------------------------- While :python:`COPY` allows to copy a legacy string as is, :python:`REPLACE` (from `fluent.migrate`) allows to replace content while performing the migration. This is necessary, for example, when migrating strings that include placeholders or entities that need to be replaced to adapt to Fluent syntax. Consider for example the following string: .. code-block:: DTD Which needs to be migrated to: .. code-block:: fluent features-title = { -brand-short-name } Features The entity :js:`&brandShortName;` needs to be replaced with a term reference: .. code-block:: python FTL.Message( id=FTL.Identifier("features-title"), value=REPLACE( "toolkit/chrome/global/aboutSupport.dtd", "aboutSupport.featuresTitle", { "&brandShortName;": TERM_REFERENCE("brand-short-name"), }, ) ), This creates an :python:`FTL.Message`, taking the value from the legacy string :js:`aboutSupport.featuresTitle`, but replacing the specified text with a Fluent term reference. .. note:: :python:`REPLACE` replaces all occurrences of the specified text. It’s also possible to replace content with a specific text: in that case, it needs to be defined as a :python:`TextElement`. For example, to replace :js:`example.com` with HTML markup: .. code-block:: python value=REPLACE( "browser/chrome/browser/preferences/preferences.properties", "searchResults.sorryMessageWin", { "example.com": FTL.TextElement('') } ) The situation is more complex when a migration recipe needs to replace :js:`printf` arguments like :js:`%S`. In fact, the format used for localized and source strings doesn’t need to match, and the two following strings using unordered and ordered argument are perfectly equivalent: .. code-block:: properties btn-quit = Quit %S btn-quit = Quit %1$S In this scenario, replacing :js:`%S` would work on the first version, but not on the second, and there’s no guarantee that the localized string uses the same format as the source string. Consider also the following string that uses :js:`%S` for two different variables, implicitly relying on the order in which the arguments appear: .. code-block:: properties updateFullName = %S (%S) And the target Fluent string: .. code-block:: fluent update-full-name = { $name } ({ $buildID }) As indicated, :python:`REPLACE` would replace all occurrences of :js:`%S`, so only one variable could be set. The string needs to be normalized and treated like: .. code-block:: properties updateFullName = %1$S (%2$S) This can be obtained by calling :python:`REPLACE` with :python:`normalize_printf=True`: .. code-block:: python FTL.Message( id=FTL.Identifier("update-full-name"), value=REPLACE( "toolkit/chrome/mozapps/update/updates.properties", "updateFullName", { "%1$S": VARIABLE_REFERENCE("name"), "%2$S": VARIABLE_REFERENCE("buildID"), }, normalize_printf=True ) ) .. attention:: To avoid any issues :python:`normalize_printf=True` should always be used when replacing :js:`printf` arguments. This is the default behaviour when working with .properties files. .. note:: :python:`VARIABLE_REFERENCE`, :python:`MESSAGE_REFERENCE`, and :python:`TERM_REFERENCE` are helper Transforms which can be used to save keystrokes in common cases where using the raw AST is too verbose. :python:`VARIABLE_REFERENCE` is used to create a reference to a variable, e.g. :js:`{ $variable }`. :python:`MESSAGE_REFERENCE` is used to create a reference to another message, e.g. :js:`{ another-string }`. :python:`TERM_REFERENCE` is used to create a reference to a `term`__, e.g. :js:`{ -brand-short-name }`. Both Transforms need to be imported at the beginning of the recipe, e.g. :python:`from fluent.migrate.helpers import VARIABLE_REFERENCE` __ https://projectfluent.org/fluent/guide/terms.html Trimming Unnecessary Whitespaces in Translations ------------------------------------------------ .. note:: This section was updated in May 2020 to reflect the change to the default behavior: legacy translations are now trimmed, unless the :python:`trim` parameter is set explicitly. It’s not uncommon to have strings with unnecessary leading or trailing spaces in legacy translations. These are not meaningful, don’t have practical results on the way the string is displayed in products, and are added mostly for formatting reasons. For example, consider this DTD string: .. code-block:: DTD Some of them might be confusing. Some are for diagnostic purposes only.
And some are omitted because they require query strings."> By default, the :python:`COPY`, :python:`REPLACE`, and :python:`PLURALS` transforms will strip the leading and trailing whitespace from each line of the translation, as well as the empty leading and trailing lines. The above string will be migrated as the following Fluent message, despite copious indentation on the second and the third line in the original: .. code-block:: fluent about-about-note = This is a list of “about” pages for your convenience.
Some of them might be confusing. Some are for diagnostic purposes only.
And some are omitted because they require query strings. To disable the default trimming behavior, set :python:`trim:"False"` or :python:`trim=False`, depending on the context: .. code-block:: python transforms_from( """ about-about-note = { COPY("toolkit/chrome/global/aboutAbout.dtd", "aboutAbout.note", trim:"False") } """) FTL.Message( id=FTL.Identifier("discover-description"), value=REPLACE( "toolkit/chrome/mozapps/extensions/extensions.dtd", "discover.description2", { "&brandShortName;": TERM_REFERENCE("-brand-short-name") }, trim=False ) ), Concatenating Strings --------------------- It's best practice to only expose complete phrases to localization, and to avoid stitching localized strings together in code. With `DTD` and `properties`, there were few options. So when migrating to Fluent, you'll find it quite common to concatenate multiple strings coming from `DTD` and `properties`, for example to create sentences with HTML markup. It’s possible to concatenate strings and text elements in a migration recipe using the :python:`CONCAT` Transform. Note that in case of simple migrations using :python:`transforms_from`, the concatenation is carried out implicitly by using the Fluent syntax interleaved with :python:`COPY()` transform calls to define the migration recipe. Consider the following example: .. code-block:: properties # %S is replaced by a link, using searchResults.needHelpSupportLink as text searchResults.needHelp = Need help? Visit %S # %S is replaced by "Firefox" searchResults.needHelpSupportLink = %S Support In Fluent: .. code-block:: fluent search-results-need-help-support-link = Need help? Visit { -brand-short-name } Support This is quite a complex migration: it requires to take 2 legacy strings, and concatenate their values with HTML markup. Here’s how the Transform is defined: .. code-block:: python FTL.Message( id=FTL.Identifier("search-results-help-link"), value=REPLACE( "browser/chrome/browser/preferences/preferences.properties", "searchResults.needHelp", { "%S": CONCAT( FTL.TextElement(''), REPLACE( "browser/chrome/browser/preferences/preferences.properties", "searchResults.needHelpSupportLink", { "%1$S": TERM_REFERENCE("brand-short-name"), }, normalize_printf=True ), FTL.TextElement("") ) } ) ), :js:`%S` in :js:`searchResults.needHelpSupportLink` is replaced by a reference to the term :js:`-brand-short-name`, migrating from :js:`%S Support` to :js:`{ -brand-short-name } Support`. The result of this operation is then inserted between two text elements to create the anchor markup. The resulting text is finally used to replace :js:`%S` in :js:`searchResults.needHelp`, and used as value for the FTL message. .. important:: When concatenating existing strings, avoid introducing changes to the original text, for example adding spaces or punctuation. Each language has its own rules, and this might result in poor migrated strings. In case of doubt, always ask for feedback. When more than 1 element is passed in to concatenate, :python:`CONCAT` disables whitespace trimming described in the section above on all legacy Transforms passed into it: :python:`COPY`, :python:`REPLACE`, and :python:`PLURALS`, unless the :python:`trim` parameters has been set explicitly on them. This helps ensure that spaces around segments are not lost during the concatenation. When only a single element is passed into :python:`CONCAT`, however, the trimming behavior is not altered, and follows the rules described in the previous section. This is meant to make :python:`CONCAT(COPY())` equivalent to a bare :python:`COPY()`. Plural Strings -------------- Migrating plural strings from `.properties` files usually involves two Transforms from :python:`fluent.migrate.transforms`: the :python:`REPLACE_IN_TEXT` Transform takes TextElements as input, making it possible to pass it as the foreach function of the :python:`PLURALS` Transform. Consider the following legacy string: .. code-block:: properties # LOCALIZATION NOTE (disableContainersOkButton): Semi-colon list of plural forms. # See: http://developer.mozilla.org/en/docs/Localization_and_Plurals # #1 is the number of container tabs disableContainersOkButton = Close #1 Container Tab;Close #1 Container Tabs In Fluent: .. code-block:: fluent containers-disable-alert-ok-button = { $tabCount -> [one] Close { $tabCount } Container Tab *[other] Close { $tabCount } Container Tabs } This is how the Transform for this string is defined: .. code-block:: python FTL.Message( id=FTL.Identifier("containers-disable-alert-ok-button"), value=PLURALS( "browser/chrome/browser/preferences/preferences.properties", "disableContainersOkButton", VARIABLE_REFERENCE("tabCount"), lambda text: REPLACE_IN_TEXT( text, { "#1": VARIABLE_REFERENCE("tabCount") } ) ) ) The `PLURALS` Transform will take care of creating the correct number of plural categories for each language. Notice how `#1` is replaced for each of these variants with :js:`{ $tabCount }`, using :python:`REPLACE_IN_TEXT` and :python:`VARIABLE_REFERENCE("tabCount")`. In this case it’s not possible to use :python:`REPLACE` because it takes a file path and a message ID as arguments, whereas here the recipe needs to operate on regular text. The replacement is performed on each plural form of the original string, where plural forms are separated by a semicolon. Explicit Variants ----------------- Explicitly creating variants of a string is useful for platform-dependent terminology, but also in cases where you want a one-vs-many split of a string. It’s always possible to migrate strings by manually creating the underlying AST structure. Consider the following complex Fluent string: .. code-block:: fluent use-current-pages = .label = { $tabCount -> [1] Use Current Page *[other] Use Current Pages } .accesskey = C The migration for this string is quite complex: the :js:`label` attribute is created from 2 different legacy strings, and it’s not a proper plural form. Notice how the first string is associated to the :js:`1` case, not the :js:`one` category used in plural forms. For these reasons, it’s not possible to use :python:`PLURALS`, the Transform needs to be crafted recreating the AST. .. code-block:: python FTL.Message( id=FTL.Identifier("use-current-pages"), attributes=[ FTL.Attribute( id=FTL.Identifier("label"), value=FTL.Pattern( elements=[ FTL.Placeable( expression=FTL.SelectExpression( selector=VARIABLE_REFERENCE("tabCount"), variants=[ FTL.Variant( key=FTL.NumberLiteral("1"), default=False, value=COPY( "browser/chrome/browser/preferences/main.dtd", "useCurrentPage.label", ) ), FTL.Variant( key=FTL.Identifier("other"), default=True, value=COPY( "browser/chrome/browser/preferences/main.dtd", "useMultiple.label", ) ) ] ) ) ] ) ), FTL.Attribute( id=FTL.Identifier("accesskey"), value=COPY( "browser/chrome/browser/preferences/main.dtd", "useCurrentPage.accesskey", ) ), ], ), This Transform uses several concepts already described in this document. Notable is the :python:`SelectExpression` inside a :python:`Placeable`, with an array of :python:`Variant` objects. Exactly one of those variants needs to have ``default=True``. This example can still use :py:func:`transforms_from()``, since existing strings are copied without interpolation. .. code-block:: python transforms_from( """ use-current-pages = .label = { $tabCount -> [1] { COPY(main_dtd, "useCurrentPage.label") } *[other] { COPY(main_dtd, "useMultiple.label") } } .accesskey = { COPY(main_dtd, "useCurrentPage.accesskey") } """, main_dtd="browser/chrome/browser/preferences/main.dtd" )