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emscripten docs: reword introduction

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in particular, remove mention of `nix-env`

Co-authored by: Henrik Karlsson <i97henka@gmail.com>
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Valentin Gagarin 2023-10-02 16:57:21 +02:00 committed by fricklerhandwerk
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doc/languages-frameworks/emscripten.section.md
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@ -2,37 +2,16 @@
[Emscripten](https://github.com/kripken/emscripten): An LLVM-to-JavaScript Compiler
This section of the manual covers how to use `emscripten` in nixpkgs.
If you want to work with `emcc`, `emconfigure` and `emmake` as you are used to from Ubuntu and similar distributions,
Minimal requirements:
* nix
* nixpkgs
Modes of use of `emscripten`:
* **Imperative usage** (on the command line):
If you want to work with `emcc`, `emconfigure` and `emmake` as you are used to from Ubuntu and similar distributions you can use these commands:
* `nix-env -f "<nixpkgs>" -iA emscripten`
* `nix-shell -p emscripten`
* **Declarative usage**:
This mode is far more power full since this makes use of `nix` for dependency management of emscripten libraries and targets by using the `mkDerivation` which is implemented by `pkgs.emscriptenStdenv` and `pkgs.buildEmscriptenPackage`. The source for the packages is in `pkgs/top-level/emscripten-packages.nix` and the abstraction behind it in `pkgs/development/em-modules/generic/default.nix`. From the root of the nixpkgs repository:
* build and install all packages:
* `nix-env -iA emscriptenPackages`
* dev-shell for zlib implementation hacking:
* `nix-shell -A emscriptenPackages.zlib`
## Imperative usage {#imperative-usage}
```console
nix-shell -p emscripten
```
A few things to note:
* `export EMCC_DEBUG=2` is nice for debugging
* `~/.emscripten`, the build artifact cache sometimes creates issues and needs to be removed from time to time
* The build artifact cache in `~/.emscripten` sometimes creates issues and needs to be removed from time to time
## Declarative usage {#declarative-usage}
@ -41,16 +20,13 @@ Let's see two different examples from `pkgs/top-level/emscripten-packages.nix`:
* `pkgs.zlib.override`
* `pkgs.buildEmscriptenPackage`
Both are interesting concepts.
A special requirement of the `pkgs.buildEmscriptenPackage` is the `doCheck = true`.
This means each Emscripten package requires that a [`checkPhase`](#ssec-check-phase) is implemented.
A special requirement of the `pkgs.buildEmscriptenPackage` is the `doCheck = true` is a default meaning that each emscriptenPackage requires a `checkPhase` implemented.
* Use `export EMCC_DEBUG=2` from within a phase to get more detailed debug output what is going wrong.
* The cache at `~/.emscripten` requires to set `HOME=$TMPDIR` in individual phases.
This makes compilation slower but also more deterministic.
* Use `export EMCC_DEBUG=2` from within a emscriptenPackage's `phase` to get more detailed debug output what is going wrong.
* ~/.emscripten cache is requiring us to set `HOME=$TMPDIR` in individual phases. This makes compilation slower but also makes it more deterministic.
### Usage 1: pkgs.zlib.override {#usage-1-pkgs.zlib.override}
This example uses `zlib` from nixpkgs but instead of compiling **C** to **ELF** it compiles **C** to **JS** since we were using `pkgs.zlib.override` and changed stdenv to `pkgs.emscriptenStdenv`. A few adaptions and hacks were set in place to make it working. One advantage is that when `pkgs.zlib` is updated, it will automatically update this package as well. However, this can also be the downside...
See the `zlib` example:
@ -174,9 +150,3 @@ Use `nix-shell -I nixpkgs=/some/dir/nixpkgs -A emscriptenPackages.libz` and from
5. `configurePhase`
6. `buildPhase`
7. ... happy hacking...
## Summary {#summary}
Using this toolchain makes it easy to leverage `nix` from NixOS, MacOSX or even Windows (WSL+ubuntu+nix). This toolchain is reproducible, behaves like the rest of the packages from nixpkgs and contains a set of well working examples to learn and adapt from.
If in trouble, ask the maintainers.