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Move all nixpkgs doc files in to the doc directory
This makes a makefile-driven developer workflow nicer.
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Graham Christensen
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16 changed files with 242 additions and 239 deletions
185
doc/languages-frameworks/emscripten.section.md
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doc/languages-frameworks/emscripten.section.md
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# User's Guide to Emscripten in Nixpkgs
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[Emscripten](https://github.com/kripken/emscripten): An LLVM-to-JavaScript Compiler
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This section of the manual covers how to use `emscripten` in nixpkgs.
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Minimal requirements:
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* nix
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* nixpkgs
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Modes of use of `emscripten`:
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* **Imperative usage** (on the command line):
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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:
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* `nix-env -i emscripten`
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* `nix-shell -p emscripten`
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* **Declarative usage**:
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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`.
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* build and install all packages:
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* `nix-env -iA emscriptenPackages`
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* dev-shell for zlib implementation hacking:
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* `nix-shell -A emscriptenPackages.zlib`
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## Imperative usage
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A few things to note:
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* `export EMCC_DEBUG=2` is nice for debugging
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* `~/.emscripten`, the build artifact cache sometimes creates issues and needs to be removed from time to time
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## Declarative usage
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Let's see two different examples from `pkgs/top-level/emscripten-packages.nix`:
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* `pkgs.zlib.override`
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* `pkgs.buildEmscriptenPackage`
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Both are interesting concepts.
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A special requirement of the `pkgs.buildEmscriptenPackage` is the `doCheck = true` is a default meaning that each emscriptenPackage requires a `checkPhase` implemented.
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* Use `export EMCC_DEBUG=2` from within a emscriptenPackage's `phase` to get more detailed debug output what is going wrong.
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* ~/.emscripten cache is requiring us to set `HOME=$TMPDIR` in individual phases. This makes compilation slower but also makes it more deterministic.
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### Usage 1: pkgs.zlib.override
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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...
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See the `zlib` example:
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zlib = (pkgs.zlib.override {
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stdenv = pkgs.emscriptenStdenv;
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}).overrideDerivation
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(old: rec {
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buildInputs = old.buildInputs ++ [ pkgconfig ];
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# we need to reset this setting!
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NIX_CFLAGS_COMPILE="";
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configurePhase = ''
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# FIXME: Some tests require writing at $HOME
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HOME=$TMPDIR
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runHook preConfigure
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#export EMCC_DEBUG=2
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emconfigure ./configure --prefix=$out --shared
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runHook postConfigure
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'';
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dontStrip = true;
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outputs = [ "out" ];
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buildPhase = ''
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emmake make
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'';
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installPhase = ''
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emmake make install
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'';
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checkPhase = ''
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echo "================= testing zlib using node ================="
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echo "Compiling a custom test"
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set -x
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emcc -O2 -s EMULATE_FUNCTION_POINTER_CASTS=1 test/example.c -DZ_SOLO \
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libz.so.${old.version} -I . -o example.js
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echo "Using node to execute the test"
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${pkgs.nodejs}/bin/node ./example.js
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set +x
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if [ $? -ne 0 ]; then
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echo "test failed for some reason"
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exit 1;
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else
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echo "it seems to work! very good."
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fi
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echo "================= /testing zlib using node ================="
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'';
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postPatch = pkgs.stdenv.lib.optionalString pkgs.stdenv.isDarwin ''
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substituteInPlace configure \
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--replace '/usr/bin/libtool' 'ar' \
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--replace 'AR="libtool"' 'AR="ar"' \
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--replace 'ARFLAGS="-o"' 'ARFLAGS="-r"'
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'';
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});
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### Usage 2: pkgs.buildEmscriptenPackage
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This `xmlmirror` example features a emscriptenPackage which is defined completely from this context and no `pkgs.zlib.override` is used.
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xmlmirror = pkgs.buildEmscriptenPackage rec {
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name = "xmlmirror";
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buildInputs = [ pkgconfig autoconf automake libtool gnumake libxml2 nodejs openjdk json_c ];
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nativeBuildInputs = [ pkgconfig zlib ];
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src = pkgs.fetchgit {
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url = "https://gitlab.com/odfplugfest/xmlmirror.git";
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rev = "4fd7e86f7c9526b8f4c1733e5c8b45175860a8fd";
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sha256 = "1jasdqnbdnb83wbcnyrp32f36w3xwhwp0wq8lwwmhqagxrij1r4b";
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};
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configurePhase = ''
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rm -f fastXmlLint.js*
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# a fix for ERROR:root:For asm.js, TOTAL_MEMORY must be a multiple of 16MB, was 234217728
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# https://gitlab.com/odfplugfest/xmlmirror/issues/8
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sed -e "s/TOTAL_MEMORY=234217728/TOTAL_MEMORY=268435456/g" -i Makefile.emEnv
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# https://github.com/kripken/emscripten/issues/6344
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# https://gitlab.com/odfplugfest/xmlmirror/issues/9
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sed -e "s/\$(JSONC_LDFLAGS) \$(ZLIB_LDFLAGS) \$(LIBXML20_LDFLAGS)/\$(JSONC_LDFLAGS) \$(LIBXML20_LDFLAGS) \$(ZLIB_LDFLAGS) /g" -i Makefile.emEnv
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# https://gitlab.com/odfplugfest/xmlmirror/issues/11
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sed -e "s/-o fastXmlLint.js/-s EXTRA_EXPORTED_RUNTIME_METHODS='[\"ccall\", \"cwrap\"]' -o fastXmlLint.js/g" -i Makefile.emEnv
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'';
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buildPhase = ''
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HOME=$TMPDIR
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make -f Makefile.emEnv
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'';
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outputs = [ "out" "doc" ];
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installPhase = ''
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mkdir -p $out/share
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mkdir -p $doc/share/${name}
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cp Demo* $out/share
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cp -R codemirror-5.12 $out/share
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cp fastXmlLint.js* $out/share
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cp *.xsd $out/share
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cp *.js $out/share
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cp *.xhtml $out/share
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cp *.html $out/share
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cp *.json $out/share
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cp *.rng $out/share
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cp README.md $doc/share/${name}
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'';
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checkPhase = ''
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'';
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};
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### Declarative debugging
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Use `nix-shell -I nixpkgs=/some/dir/nixpkgs -A emscriptenPackages.libz` and from there you can go trough the individual steps. This makes it easy to build a good `unit test` or list the files of the project.
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1. `nix-shell -I nixpkgs=/some/dir/nixpkgs -A emscriptenPackages.libz`
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2. `cd /tmp/`
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3. `unpackPhase`
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4. cd libz-1.2.3
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5. `configurePhase`
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6. `buildPhase`
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7. ... happy hacking...
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## Summary
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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.
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If in trouble, ask the maintainers.
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