Build bootstrap with an explicit target

[chenyukang]

Fixes #155651

[rustbot]

r? @Mark-Simulacrum

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[Kobzol]

This sounds like a hack to make bootstrap match a specific kind of Cargo config. We should instead ask Cargo where was the generated binary stored, or use cargo run, or something like that.

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[chenyukang]

oh, I did something wrong on Git and closed it.

[chenyukang]

This sounds like a hack to make bootstrap match a specific kind of Cargo config. We should instead ask Cargo where was the generated binary stored, or use cargo run, or something like that.

This is not trying to guess an arbitrary Cargo output path. We explicitly pass --target self.build, so the bootstrap binary location follows Cargo’s normal target-dir layout under CARGO_TARGET_DIR//debug. This relies on Cargo’s standard target-dir layout.

I tried to use cargo run directly, it will involve more changes because of CI testing.

By “ask Cargo where the generated binary was stored”, do you mean using Cargo’s JSON messages and reading the compiler-artifact.executable field?