Migrate `libs-through-symlink` to rmake.rs
Part of https://github.com/rust-lang/rust/issues/121876.
This PR migrates `tests/run-make/libs-through-symlink/` to use rmake.rs.
- Regression test for #13890.
- Original fix PR is #13903.
- Document test intent, backlink to #13890 and fix PR #13903.
- Fix the test logic: the `Makefile` version seems to not actually be exercising the "library search traverses symlink" logic, because the actual symlinked-to-library is present under the `$(TMPDIR)` directory tree when `bar.rs` is compiled, because the `$(RUSTC)` invocation has an implicit `-L $(TMPDIR)`. The symlink itself was actually broken, i.e. it should've been `ln -nsf $(TMPDIR)/outdir/$(NAME) $(TMPDIR)` but it used `ln -nsf outdir/$(NAME) $(TMPDIR)`. The rmake.rs version now explicitly separates the two directory trees and sets the CWD of the `bar.rs` rustc invocation so that the actual library is *not* present under its CWD tree.
I.e. it is now
```
$test_output/ # rustc foo.rs -o actual_lib_dir/libfoo.rlib
actual_lib_dir/
libfoo.rlib
symlink_lib_dir/ # CWD set; rustc -L . bar.rs
libfoo.rlib --> $test_output/actual_lib_dir/libfoo.rlib
```
Partially supersedes #129011.
This PR is co-authored with `@Oneirical.`
r? compiler
The run-make test suite contains tests which are the most flexible out of all
the rust-lang/rust test suites. run-make
tests can basically contain arbitrary code, and are supported by the
run_make_support library.
Infrastructure
There are two kinds of run-make tests:
The new rmake.rs version: this allows run-make tests to be written in Rust
(with rmake.rs as the main test file).
The legacy Makefile version: this is what run-make tests were written with
before support for rmake.rs was introduced.
The implementation for collecting and building the rmake.rs recipes (or
Makefiles) are in
src/tools/compiletest/src/runtest.rs,
in run_rmake_v2_test and run_rmake_legacy_test.
Rust-based run-make tests: rmake.rs
The setup for the rmake.rs version is a 3-stage process:
First, we build the run_make_support library in bootstrap as a tool lib.
Then, we compile the rmake.rs "recipe" linking the support library and its
dependencies in, and provide a bunch of env vars. We setup a directory
structure within build/<target>/test/run-make/
<test-name>/
rmake.exe # recipe binary
rmake_out/ # sources from test sources copied over
and copy non-rmake.rs input support files over to rmake_out/. The
support library is made available as an extern prelude.
Finally, we run the recipe binary and set rmake_out/ as the working
directory.
Formatting
Note that files under tests/ are not formatted by ./x fmt,
use rustfmt tests/path/to/file.rs to format a specific file if desired.
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