fa883cb647
Add PROC_MACRO_TEST_TOOLCHAIN environment variable
This allows overriding the toolchain used to run `proc-macro-srv` tests.
---
Sample usage.
Testing the current ABI (variable unset/empty):
```shell
amos@tails ~/bearcove/rust-analyzer/crates/proc-macro-srv proc-macro-test-toolchain*
❯ PROC_MACRO_TEST_TOOLCHAIN="" cargo test --quiet
running 16 tests
................
test result: ok. 16 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.01s
```
Testing an older ABI:
```shell
amos@tails ~/bearcove/rust-analyzer/crates/proc-macro-srv proc-macro-test-toolchain*
❯ PROC_MACRO_TEST_TOOLCHAIN="1.58" cargo test --quiet
running 16 tests
................
test result: ok. 16 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.01s
```
Testing current nightly ABI:
```shell
❯ rustc +nightly --version
rustc 1.64.0-nightly (
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imp | ||
src | ||
build.rs | ||
Cargo.toml |