Update rust_bindgen_library to only link into the direct consumer
#2361
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UebelAndre
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rust_bindgen_library to only link cc_lib into the direct c…rust_bindgen_library to only link into the direct consumer
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Generally looks reasonable, added a few thoughts
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@illicitonion this good to go? |
Co-authored-by: Daniel Wagner-Hall <[email protected]>
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### Problem
As of now (before this PR), we seem to mix `link_flags` file into using
for two purposes.
For
```
cc_library(
name = "simple",
srcs = ["simple.cc"],
hdrs = ["simple.h"],
linkopts = ["-framework"],
)
rust_bindgen_library(
name = "simple_bindgen",
cc_lib = ":simple",
header = "simple.h",
)
rust_binary(
name = "simple_example",
srcs = ["main.rs"],
deps = [":simple_bindgen"],
)
```
`rust_bindgen_library` produces a `link_flags` file with
```
-lstatic=simple
-C
link-args=-framework
```
`-lstatic=simple` is consumed by `rustc` whereas `-framework` is
expected to be consumed by an actual linker (either invoked by `rustc`
or `cc_common.link`)
The flags are then passed to `rustc` command to compile
`libsimple_bindgen.rlib`. It does not yield any error because
`-lstatic=simple` is correctly used whereas `-framework` is no-op (there
is no linker being invoked for producing `rlib`). However, the rustc
***doesn't*** pass `-framework` to the linker that link the
`rust_binary` (which is where the cc linkopts matters).
Another problem is that this approach is not compatible with
`experimental_use_cc_common_link` option which let `cc_common.link`
instead of `rustc` invoke the linker. See #2413
### Solution
We're referring "link" as at least two things (which I think what causes
problem here):
1.
https://doc.rust-lang.org/rustc/command-line-arguments.html#-l-link-the-generated-crate-to-a-native-library
2. https://doc.rust-lang.org/rustc/codegen-options/index.html#linker
https://doc.rust-lang.org/rustc/codegen-options/index.html#link-args
As proposed in
#2415 (comment),
this PR splits `<rust_library_bindgen>__bindgen.link_flags` produced by
`rust_bindgen` rule into two files:
1. `rustc_flags`
```
-lstatic=simple
```
2. `linker_flags`
```
-framework
```
We "sort-of" (but not perfectly) had it correct before
#2361 when we link the
binary directly with the cc_library (aka both kinds of flags).
But since we want to support the Cargo style of linking
```
cc_lib -> bindgen -> lib_a -> bin
```
instead of
```
cc_lib -> bindgen -> lib_a -> bin
\___________________________^
```
we can pass `-lstatic=simple` to the `rustc` command that builds
`simple_bindgen` (rust_library) and propagate `linkopts` to
`simple_example` (rust_binary) so that the linker can use it.
```
cc_library -> rust_bindgen -> rust_library -> rust_binary
-lstatic=simple
-Clink-args="-framework"
```
This is long and sounds like a proposal. I'm open for suggestion
@UebelAndre @illicitonion @krasimirgg
Fixes #2413
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Most uses of bindgen are via build scripts which typically use either
-Lnative=to specify linker paths for the current target being built. The way the rules are currently defined, has the bindgen library linked directly into the final library which leads to some annoying ordering errors compared to the same project building with Cargo. This PR aims to support the Cargo style of linking via aleak_symbols = Falseflag, thus changing the dependency graph when linking from:to:
Note that
leak_symbolsis intended to be used as an escape hatch to restore the original behavior and will be deleted in the future.