fix: Recompiles due to RUSTC_BOOTSTRAP #16621
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Some packages (e.g. thiserror) force a recompile if the value of the `RUSTC_BOOTSTRAP` env var changes. RA sets the variable to 1 in order to enable rustc / cargo unstable options it uses. This causes flapping recompiles when building outside of RA. As of Cargo 1.75 the `--keep-going` flag is stable. This change uses the flag without `RUSTC_BOOTSTRAP` if the Cargo version is >= 1.75, and drops `--keep-going` otherwise. This fixes build script recompilation.
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`cargo rustc -- <args>` first builds dependencies then calls `rustc <args>` for the current package. Here, we don't want to build dependencies, we just want to call `rustc --print`. An unstable `cargo rustc` `--print` command bypasses building dependencies first. This speeds up execution of this code path and ensures RA doesn't recompile dependencies with the `RUSTC_BOOTSRAP=1` env var flag set. Note that we must pass `-Z unstable-options` twice, first to enable the `cargo` unstable `--print` flag, then later to enable the unstable `rustc` `target-spec-json` print request.
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| .args([ | ||
| "rustc", | ||
| "-Z", | ||
| "unstable-options", | ||
| "--print", | ||
| "target-spec-json", | ||
| "--", | ||
| "-Z", | ||
| "unstable-options", | ||
| ]) |
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Is this an accidental change (from debugging perhaps)?
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While it looks wonky, it's intended. I explained it in the commit message for this change, which I'm pasting here:
cargo rustc -- <args>first builds dependencies then callsrustc <args>for the current package. Here, we don't want to build dependencies, we just want to callrustc --print. An unstablecargo rustcRUSTC_BOOTSRAP=1env var flag set.Note that we must pass
-Z unstable-optionstwice, first to enable thecargounstablerustctarget-spec-jsonprint request.
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Oh I see, I was very confused by the invoked command as it looks somewhat funny 😅
This is a great change thanks, I've been wondering if we could do better as one other downside of the current command is that it doesnt work in virtual workspaces, whereas this does!
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Thanks! This is a nice small change! |
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☀️ Test successful - checks-actions |
Some packages (e.g. thiserror) force a recompile if the value of the
RUSTC_BOOTSTRAPenv var changes. RA sets the variable to 1 in order to enable rustc / cargo unstable options. This causes flapping recompiles when building outside of RA.Fixes #15057