How to produce .WASM fille

[Buddy-87]

Hello

I would like to ask if it is possible to find out the exact process behind creating the icu_capi.wasm file inside the project 'https://www.npmjs.com/package/icu'.

The reason Why I am asking is that we would like to use just a part of the ICU for the application. Without the need to use/ship the whole 15 MB file. I know there is a possibility to use the 'icu4x-datagen' to select the data more specifically. But I was not able to find how specifically it is converted into the wasm format.

Let's say I want only limited number of locales and only Date and Time formatters.

Thank you

[robertbastian]

The WASM file is a build of the icu_capi Rust crate. There are multiple ways to make it smaller:

• exclude compiled data. This will then require using icu4x-datagen and managing your own data, which can be made smaller than the compiled data by selected fewer locales. See our tutorial here: https://icu4x.unicode.org/2_1/tutorials/date-picker-data/
  • Build icu_capi without the compiled_data feature
• exclude certain components, such as collation using Cargo (Rust's build system) features
  • Build icu_capi with only the datetime feature, for example
• exclude certain APIs using a linker script (advanced)
  • Example: https://github.com/unicode-org/icu4x/blob/main/examples/js-tiny/Makefile

To build icu_capi.wasm, you need a Rust toolchain. Check out the repo, and run this Makefile, with the desired FEATURES: https://github.com/unicode-org/icu4x/blob/release/2.1/ffi/npm/Makefile

[robertbastian]

The list of features for the icu_capi crate: https://docs.rs/crate/icu_capi/latest/features

[Buddy-87]

Hello I am not sure if this will be exactly in the scope of this question. But running that small example I have more questions than answers. I will start with the part that is not working for me.

Mac Machine

I am using Apple's sillicon and the MacOS seq. 17.2. And there is an issue which I do not fully understand in the Makefile. More specifically it is the line :

        # RUSTFLAGS="-Cpanic=abort -Copt-level=s -C link-arg=-zstack-size=${WASM_STACK_SIZE} -Clinker-plugin-lto -Ccodegen-units=1 -C linker=${BASEDIR}/ld.py -C linker-flavor=wasm-ld -$
        RUSTFLAGS="-Cpanic=abort -Copt-level=s -C link-arg=-zstack-size=${WASM_STACK_SIZE} -Clinker-plugin-lto -Ccodegen-units=1 -Clto -Cembed-bitcode -Zwasm-c-abi=spec"

Only with this change something actually compiled. Which means disable the linker. But the make test throws error. If has however compiled the 'icu_capi.wasm' file. That is quite large around 12 MB. But the cost is that it does not probably work as intended.

And basically the problem is most likely with the linker ld.py. Because no matter what I install the command on the line 35 inside the 'ld.py' is restult = subprocess.run(["lld-19"] + ...). The 'lld-19' simply does not exist. I have installed the llvm via brew and checked if the paths are exported in the '.zshrc' file, and point to the right locations. And yes they do exist, but this part does not work.

Linux Machine

So the second attempt was to run the same Makefile on my older Linux machine. Also I had issue with the same line in the python script. However. I did not change anything in the Makefile. Only thing I changed was the 'lld-19' to 'wasm-ld'. On that computer the make test returns the magical Output is ১০,০০০.০৭. Which I am assuming that is correct. But both times I had to edit the 'ld.py'. And I am not sure what is the correct way to go from here.

But also if I run the python script alone with the updated version of lld value I get: wasm-ld: error: no input files. This also adds to the confusion.

To sum it up

I have to my best knowledge on both the machines successfully installed the required tools. Such as rustup (like rustup target add wasm32-unknown-unknown --toolchain nightly-2025-02-17) and other tools. Both machines produces some output. But on MacOs I did not crack the correct solution.

So one of the important questions is also what does the 'pd.py' suppose to actually do.

[sffc]

It appears you are asking questions about the "advanced" option. As the author of that example (the Makefile and ld.py), I can say that there is woefully little documentation on this subject. Although I'm not in a good position to help you debug your bash script commands, I can try to offer more documentation on what all the different flags mean and what they are used for: #7255

[sffc]

You might find it helpful to see the GitHub Actions configurations for this test, in order to help reproduce it locally.