Incorrect linker flags when using cc_common.link
#2413
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UebelAndre
added
bug
bindgen
ghost
mentioned this issue
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Thank you for filling this issue @daivinhtran, I should have done it myself… I've opened a PR to attempt to fix this issue: #2415 I've never used |
daivinhtran
pushed a commit
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Feb 16, 2024
### 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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See #2407 (comment) for more context. I believe #2407 breaks any user that uses
cc_common.linkfor linking.Filing a bug so we can triage and prioritize fixing it.
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