Setting a lower `RUST_MIN_STACK` than `DEFAULT_STACK_SIZE` increases stack??? about rust HOT 12 OPEN

The default stack size of new threads is 2 MiB. However, the default stack size of the main thread varies depending on the platform and possibly platform-dependent build configuration.

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Rust does not override every last platform-specific behavior. To do so would likely be quite harmful.

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Actually, wait. I'm confused. For rustc, this shouldn't matter because of the DEFAULT_STACK_SIZE (not to be confused with the default stack size).

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@biabbas What version of rustc did you test with?

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No repro on x86_64-unknown-linux-gnu.

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Wait, I misapplied some directions.

It... does repro? What.

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@biabbas What version of rustc did you test with?

I was able to reproduce this behavior on rust 1.75, 1.78, 1.79 stable.

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The default stack size of new threads is 2 MiB. However, the default stack size of the main thread varies depending on the platform and possibly platform-dependent build configuration.

You are right, default stack size for new threads is 2mb. I went through the std thread code and I see that min_stack uses this RUST_MIN_STACK variable to influence the size of thread builder stack size. In the test case what stack is overflowed and why RUST_MIN_STACK workaround fixes it?

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Actually, wait. I'm confused. For rustc, this shouldn't matter because of the DEFAULT_STACK_SIZE (not to be confused with the default stack size).

Could you please elaborate and differentiate between the two.

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@biabbas DEFAULT_STACK_SIZE is a constant used by rustc to set the thread builder's stack amount, the "default stack size" we've mentioned in a few cases in this thread is the platform's implicit stack size for the main thread.

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Can rustc be using parallelism( sub threads with limit around 2mb) for program compilation? In that case the error message should emit the actual stack that is overflowed. I know cargo uses parallelism for build but not sure if rustc also uses this.

I had access to reproduce and work on #113612. This example would compile with RUST_MIN_STACT set to 3mb.
Maybe the thread builder stack size is overwriting the main threads stack size, in which case it needs a fix.

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Yes, we deliberately set the stack size by spawning a thread.

However, I would expect we are setting it to 8MB.

We emit a suggestion that suggests setting RUST_MIN_STACK to double the previous value.

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