Add very basic "comptime" fn implementation by oli-obk · Pull Request #148820 · rust-lang/rust

Add very basic "comptime" fn implementation

Implements functions that cannot be called at runtime (and thus also not from normal const functions, as those could be called from runtime).

This is done via the internal attribute `rustc_comptime` that can be added to normal functions, turning them into compile-time-only functions.

Because @fee1-dead and @compiler-errors did amazing work, we even get trait bounds that work inside comptime fns: via unconditionally-const `const Trait` bounds.

Use cases are

* rust-lang#146923
* const heap intrinsics
* and the other various intrinsics (e.g. size_of 😆) that will just ICE in codegen or panic at runtime if they actually end up in runtime code

project goal issue: rust-lang/rust-project-goals#406

no tracking issue until we have a feature gate and some sort of syntax

cc @scottmcm as the T-lang goal champion

…uwer

Rollup of 13 pull requests

Successful merges:

 - #147302 (asm! support for the Xtensa architecture)
 - #148820 (Add very basic "comptime" fn implementation)
 - #157299 (Fix unstable diagnostics in tests)
 - #143511 (Improve TLS codegen by marking the panic/init path as cold)
 - #154608 (Add `_value` API for number literals in proc-macro)
 - #156762 (xfs support in `test_rename_directory_to_non_empty_directory`)
 - #157300 (Relax test requirements for consistency)
 - #157383 (tests: codegen-llvm: Ignore BPF targets in c-variadic-opt)
 - #157413 (fix: don't suggest .into_iter() for .cloned()/.copied() on non-reference Option)
 - #157578 (Fix diagnostics for non-exhaustive destructuring assignments (#157553))
 - #157587 (explain that the size_of constant also serves to avoid optimizing away 'unused' size_of calls)
 - #157596 (test: remove ineffective link-extern-crate-with-drop-type test)
 - #157602 (rustdoc: Remove unnecessary fast path)

Rollup merge of #148820 - oli-obk:comptime, r=fee1-dead

Add very basic "comptime" fn implementation

Implements functions that cannot be called at runtime (and thus also not from normal const functions, as those could be called from runtime).

This is done via the internal attribute `rustc_comptime` that can be added to normal functions, turning them into compile-time-only functions.

Because @fee1-dead and @compiler-errors did amazing work, we even get trait bounds that work inside comptime fns: via unconditionally-const `const Trait` bounds.

Use cases are

* #146923
* const heap intrinsics
* and the other various intrinsics (e.g. size_of 😆) that will just ICE in codegen or panic at runtime if they actually end up in runtime code

project goal issue: rust-lang/rust-project-goals#406

no tracking issue until we have a feature gate and some sort of syntax

cc @scottmcm as the T-lang goal champion

…e1-dead

Start using comptime for reflection intrinsics and their wrapper functions

r? @fee1-dead

follow-up to rust-lang#148820

I needed to add some more rustc code because turns out I forgot to add tests to the previous PR which actually codegen while using comptime fns. Check builds never try to create optimized MIR, so no code ever hit the assert that prevents creating optimized MIR for comptime fns.

Start using comptime for reflection intrinsics and their wrapper functions

r? @fee1-dead 

follow-up to #148820 

I needed to add some more rustc code because turns out I forgot to add tests to the previous PR which actually codegen while using comptime fns. Check builds never try to create optimized MIR, so no code ever hit the assert that prevents creating optimized MIR for comptime fns.

…e1-dead

Start using comptime for reflection intrinsics and their wrapper functions

r? @fee1-dead

follow-up to rust-lang#148820

I needed to add some more rustc code because turns out I forgot to add tests to the previous PR which actually codegen while using comptime fns. Check builds never try to create optimized MIR, so no code ever hit the assert that prevents creating optimized MIR for comptime fns.

…e1-dead

Start using comptime for reflection intrinsics and their wrapper functions

r? @fee1-dead

follow-up to rust-lang#148820

I needed to add some more rustc code because turns out I forgot to add tests to the previous PR which actually codegen while using comptime fns. Check builds never try to create optimized MIR, so no code ever hit the assert that prevents creating optimized MIR for comptime fns.

…e1-dead

Start using comptime for reflection intrinsics and their wrapper functions

r? @fee1-dead

follow-up to rust-lang#148820

I needed to add some more rustc code because turns out I forgot to add tests to the previous PR which actually codegen while using comptime fns. Check builds never try to create optimized MIR, so no code ever hit the assert that prevents creating optimized MIR for comptime fns.

…e1-dead

Start using comptime for reflection intrinsics and their wrapper functions

r? @fee1-dead

follow-up to rust-lang#148820

I needed to add some more rustc code because turns out I forgot to add tests to the previous PR which actually codegen while using comptime fns. Check builds never try to create optimized MIR, so no code ever hit the assert that prevents creating optimized MIR for comptime fns.

…e1-dead

Start using comptime for reflection intrinsics and their wrapper functions

r? @fee1-dead

follow-up to rust-lang#148820

I needed to add some more rustc code because turns out I forgot to add tests to the previous PR which actually codegen while using comptime fns. Check builds never try to create optimized MIR, so no code ever hit the assert that prevents creating optimized MIR for comptime fns.

…e1-dead

Start using comptime for reflection intrinsics and their wrapper functions

r? @fee1-dead

follow-up to rust-lang#148820

I needed to add some more rustc code because turns out I forgot to add tests to the previous PR which actually codegen while using comptime fns. Check builds never try to create optimized MIR, so no code ever hit the assert that prevents creating optimized MIR for comptime fns.

…e1-dead

Start using comptime for reflection intrinsics and their wrapper functions

r? @fee1-dead

follow-up to rust-lang#148820

I needed to add some more rustc code because turns out I forgot to add tests to the previous PR which actually codegen while using comptime fns. Check builds never try to create optimized MIR, so no code ever hit the assert that prevents creating optimized MIR for comptime fns.

…e1-dead

Start using comptime for reflection intrinsics and their wrapper functions

r? @fee1-dead

follow-up to rust-lang#148820

I needed to add some more rustc code because turns out I forgot to add tests to the previous PR which actually codegen while using comptime fns. Check builds never try to create optimized MIR, so no code ever hit the assert that prevents creating optimized MIR for comptime fns.

Rollup merge of #157647 - oli-obk:start-using-comptime, r=fee1-dead

Start using comptime for reflection intrinsics and their wrapper functions

r? @fee1-dead

follow-up to #148820

I needed to add some more rustc code because turns out I forgot to add tests to the previous PR which actually codegen while using comptime fns. Check builds never try to create optimized MIR, so no code ever hit the assert that prevents creating optimized MIR for comptime fns.