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[Bazel] Support generating a secondary cache (#1405)

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This is a working solution for generating a separate Emscripten cache.
Note that this requires an additional entry in the workspace as follows:
```starlark
load("@emsdk//:emscripten_cache.bzl", emsdk_emscripten_cache = "emscripten_cache")
emsdk_emscripten_cache()
```
When used like this, the default Emscripten cache will be used. However,
if the entry is as follows:
```starlark
load("@emsdk//:emscripten_cache.bzl", emsdk_emscripten_cache = "emscripten_cache")
emsdk_emscripten_cache(flags = ["--lto"])
```
Then embuilder will be called to build all system libraries and ports
(i.e., the `ALL` option to embuilder) with the LTO option enabled. This
can take awhile, so I have also made possible to specify which libraries
you want to build explicitly:
```starlark
load("@emsdk//:emscripten_cache.bzl", emsdk_emscripten_cache = "emscripten_cache")
emsdk_emscripten_cache(
    flags = ["--lto"],
    libraries = [
        "crtbegin",
        "libprintf_long_double-debug",
        "libstubs-debug",
        "libnoexit",
        "libc-debug",
        "libdlmalloc",
        "libcompiler_rt",
        "libc++-noexcept",
        "libc++abi-debug-noexcept",
        "libsockets"
    ]
)
```

Resolves #807, resolves #971, resolves #1099, resolves #1362, resolves
#1401
This commit is contained in:
Michael Allwright
2024-07-01 18:23:07 +02:00
committed by GitHub
parent 7fbd555dbe
commit 82d41a76d3
14 changed files with 199 additions and 3 deletions
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26
bazel/README.md
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@@ -66,4 +66,30 @@ rules.
and all of its dependencies, and does not require amending `.bazelrc`. This
is the preferred way, since it also unpacks the resulting tarball.
The Emscripten cache shipped by default does not include LTO, 64-bit or PIC
builds of the system libraries and ports. If you wish to use these features you
will need to declare the cache when you register the toolchain as follows. Note
that the configuration consists of the same flags that can be passed to
embuilder. If `targets` is not provided, all system libraries and ports will be
built, i.e., the `ALL` option to embuilder.
```starlark
load("@emsdk//:toolchains.bzl", "register_emscripten_toolchains")
register_emscripten_toolchains(cache = {
"configuration": ["--lto"],
"targets": [
"crtbegin",
"libprintf_long_double-debug",
"libstubs-debug",
"libnoexit",
"libc-debug",
"libdlmalloc",
"libcompiler_rt",
"libc++-noexcept",
"libc++abi-debug-noexcept",
"libsockets"
]
})
```
See `test_external/` for an example using [embind](https://emscripten.org/docs/porting/connecting_cpp_and_javascript/embind.html).