@mozilla/properties-to-ftl
v0.1.0
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Migrate strings from .properties to Fluent in mozilla-central
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Mozilla Properties-to-Fluent Migration Helper
This tool is intended to help automate most parts of moving messages
from .properties
files in mozilla-central
to Fluent .ftl
files.
On the way there, it can also update .js
, .jsm
and .xhtml
files that use these messages,
as well as writing a .py
migration script for non-English locales.
Because this migration includes a move from indexed to named placeholders/variables,
it's run as a two-step process.
On the first run, a .migration.yaml
config file is generated next to each .properties
file.
This may then be manually verified and updated before running the same command again,
which then applies the full migration.
Install & Setup
You will need Node.js version 14 or greater to use this tool. Then:
npm install --global @mozilla/properties-to-ftl
After this, the script may be run from anywhere as properties-to-ftl
.
If you install it locally, use npx properties-to-ftl
instead.
To verify that setup was successful and see a list of command-line options, run:
properties-to-ftl --help
Usage
When migrating legacy messages, multiple things change:
- The message file extension changes, possible as well as its name.
- The file's location within
mozilla-central
changes. - Message keys change, and often gain an identifying prefix in addition to being kebab-cased.
- The syntax for referring to variables in messages changes.
- The JavaScript API for formatting messages changes.
To help with the first three, you need to either use the --ftl-path
and --ftl-prefix
options
or add some metadata comments to each .properties
file that you're migrating:
# FTL path: foo/bar/baz.ftl
# FTL prefix: foobar
These comments don't need to be stored in the repo,
but keeping them there might help if a properties file is migrated in multiple patches.
If using the corresponding command-line arguments
and the .properties
file is only partially migrated,
these metadata comments will be added to it automatically.
- The
FTL path
may use either the repo root or thelocales/en-US/
directory as its root. - An
FTL prefix
is not required, but if set, may only contain lower-case letters and dashes:^[a-z-]+$
. If set, it will be included as a prefix for all FTL message keys.
On the first run, a .migration.yaml
config file is generated next to each .properties
file.
This may then be manually verified and updated before running the same command again,
which then applies the full migration.
Command-line arguments
For full usage, run this command:
properties-to-ftl --help
When targeting a JS file, it is parsed for chrome://
references to .properties
and .xhtml
files,
which are then parsed in turn.
XHTML may include <stringbundle>
elements which are detected (and their source .properties
also parsed),
and properties files may include FTL path
references, which are also parsed.
All of those files are then modified in-place
once the migration config has been reviewed and the CLI command is run again.
When targeting a .properties
file, all of its strings are migrated to Fluent.
In this use, JS and XHTML files are not parsed or migrated,
and the placeholder variables are forced to use var#
names.
These should be individually fixed in the migration config; they will have # FIXME
comments.
Your Attention is Required
Because so many things change, it's unlikely that the script will catch everything.
Where possible, a comment /* L10N-FIXME */
is injected
immediately after points in the JS source that require human attention.
In the generated FTL file, particular care should be given to reviewing the comments, which will at least approximate the recommended metadata structurefor placeholders, but may not match exactly or be complete.
You will also need to manually make any necessary updates to jar.mn
manifest files
if a .properties
file is removed.
Migration config files should not be added to the soruce repository;
they may be safely removed at the end of the migration.
Tutorials
To best learn how all of this works, play around with it!
Follow the setup instructions,
then find a JS file in mozilla-central
that calls Services.strings.createBundle()
,
and run:
properties-to-ftl path/to/file.jsm
Based on the CLI output,
you might need to first --include
or --exclude
some .properties
file paths
and provide an --ftl-path
argument in order to generate a .migration.yaml
file
next to its source .properties
file.
Open it and the .js
or .jsm
file in an editor,
and see if you can resolve the FIXME
comments.
Then run the same CLI command again to apply your transformation.
Sometimes, everything is already perfect,
but often additional manual work is required to polish up the migration patch.
An Example Migration
As an example, the file browser/locales/en-US/chrome/browser/feeds/subscribe.properties
currently contains these messages:
addProtocolHandlerMessage=Add “%1$S” as an application for %2$S links?
addProtocolHandlerAddButton=Add application
addProtocolHandlerAddButtonAccesskey=A
Running the following command will generate a config file subscribe.migration.yaml
next to it:
properties-to-ftl --ftl-path protocolhandler.ftl \
browser/locales/en-US/chrome/browser/feeds/subscribe.properties
meta:
bug: xxxxxx # FIXME
title: Convert subscribe.properties to Fluent
ftl:
root: browser/locales/en-US
path: protocolhandler.ftl
migrate:
addProtocolHandlerMessage: # Add “%1$S” as an application for %2$S links?
key: add-protocol-handler-message
varNames:
- var1 # FIXME
- var2 # FIXME
addProtocolHandlerAddButton: # Add application
key: add-protocol-handler-add-button
addProtocolHandlerAddButtonAccesskey: # A
key: add-protocol-handler-add-button-accesskey
For a proper migration, a few things ought to be fixed here:
- The bug id needs to be included; this'll be a part of the generated Python migration script's filename.
- The
add-protocol-handler-message
variable names need to be specified. In many cases, if the command is run against a.js
or.jsm
file, these can be autodetected. In this case, based on an inspection of WebProtocolHandlerRegistrar.jsm, these should probably behost
andprotocol
. - The access key ought to be an attribute rather than a separate message.
After these changes, the migration config will look like this:
meta:
bug: 123456
title: Convert subscribe.properties to Fluent
ftl:
root: browser/locales/en-US
path: protocolhandler.ftl
migrate:
addProtocolHandlerMessage: # Add “%1$S” as an application for %2$S links?
key: add-protocol-handler-message
varNames:
- host
- protocol
addProtocolHandlerAddButton: # Add application
key: add-protocol-handler-add-button
addProtocolHandlerAddButtonAccesskey: # A
key: add-protocol-handler-add-button
attr: accesskey
Now running the properties-to-ftl
command again:
properties-to-ftl browser/locales/en-US/chrome/browser/feeds/subscribe.properties
finds the config file, and generates a new protocolhandler.ftl
:
add-protocol-handler-message = Add “{ $host }” as an application for { $protocol } links?
add-protocol-handler-add-button = Add application
.accesskey = A
as well as a corresponding bug_123456_protocolhandler.py
migration script for other locales.
NOTE: If these commands were run against WebProtocolHandlerRegistrar.jsm
(The only JS file that uses these messages) instead of subscribe.properties
,
that would have modified its source as well,
automating some of the changes needed there and marking the rest with /* L10N-FIXME */
comments.
Hacking It
This is an imperfect tool, because there's a limit to how much it makes sense to automate it. If/when you encounter issues with it, you are invited and expected to gauge for yourself how much it's really helping you, and whether it might make sense to either 1) submit a PR with a fix or 2) just deal with it.
In total, at the time of writing this, there are only about 5000 messages in properties files in mozilla-central, and many of the corner cases are relatively rarely used. So if you're encounter a problem, it may well be easier to fix it directly rather than improving this tool.
Some specific situations are recognised:
Often moving from
.properties
to Fluent should include a switch from using imperative formatting methods to e.g. DOM localization. That's a transform that can't really be automated, so the best we can do is provide a much more Fluent-ish base for your work. Applying the transformation via the JS file should also allow for decent variable name mapping, which you'd have to otherwise do manually.Much of the code under
devtools/
is using custom wrappers for localization code. While these wrappers are not directly supported, but it's still possible to force theproperties-to-ftl
JS processor to transform at least the message keys by adding a line like this to the file:Services.strings.createBundle('chrome://fake/locale/foo/bar.properties')
and as long as the
bar.properties
filename is unique, literal key value strings in that file can get appropriately transformedWhen migrating messages with plural forms, the JS calls targeting the
PluralForm
global are not automatically migrated. If such messages include#1
/#2
variables, you need to include their mapping to Fluent variables manually in the generated FTL file as well as the Python migration script, and remove the wrapping JS code that applies.replace("#1", ...)
transformations on the result.When migrating messages that are used from C++, you'll probably need to target the
.properties
file directly, and manually fill out more variable names in the migration config. Some examples for manually constructing the C++ arguments required by theLocalization
class are available inTestLocalization.cpp
.
Development
If you do find a reason to fix/improve this tool, please do file a PR to this repository with your work.
When getting started you'll need to run:
git submodule update --init
npm install
The resolve-chrome-uri
dependency is vendored in as a git submodule
because it's honestly too hacky to release for wider use.
The "tests" that are included are a couple of example migration files.