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Unconditional recursion in a const fn produces a massive diagnostic #92796

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PatchMixolydic opened this issue Jan 11, 2022 · 1 comment · Fixed by #92802
Closed

Unconditional recursion in a const fn produces a massive diagnostic #92796

PatchMixolydic opened this issue Jan 11, 2022 · 1 comment · Fixed by #92802
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@compiler-errors
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A-const-fn Area: const fn foo(..) {..}. Pure functions which can be applied at compile time. A-diagnostics Area: Messages for errors, warnings, and lints D-verbose Diagnostics: Too much output caused by a single piece of incorrect code. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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@PatchMixolydic
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PatchMixolydic commented Jan 11, 2022 •
edited by rustbot
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Given the following code (playground):

#![allow(unused)]

const fn f<T>(x: T) {
    f(x);
}

const X: () = f(1);

The current output is:

Massive diagnostic 
warning: function cannot return without recursing
 --> src/lib.rs:3:1
  |
3 | const fn f<T>(x: T) {
  | ^^^^^^^^^^^^^^^^^^^ cannot return without recursing
4 |     f(x);
  |     ---- recursive call site
  |
  = note: `#[warn(unconditional_recursion)]` on by default
  = help: a `loop` may express intention better if this is on purpose

error: any use of this value will cause an error
 --> src/lib.rs:4:5
  |
4 |     f(x);
  |     ^^^^
  |     |
  |     reached the configured maximum number of stack frames
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     inside `X` at src/lib.rs:7:15
...
7 | const X: () = f(1);
  | -------------------
  |
  = note: `#[deny(const_err)]` on by default
  = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
  = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>

Ideally, the duplicate lines should be hidden:

warning: function cannot return without recursing
 --> src/lib.rs:3:1
  |
3 | const fn f<T>(x: T) {
  | ^^^^^^^^^^^^^^^^^^^ cannot return without recursing
4 |     f(x);
  |     ---- recursive call site
  |
  = note: `#[warn(unconditional_recursion)]` on by default
  = help: a `loop` may express intention better if this is on purpose

error: any use of this value will cause an error
 --> src/lib.rs:4:5
  |
4 |     f(x);
  |     ^^^^
  |     |
  |     reached the configured maximum number of stack frames
  |     inside `f::<i32>` at src/lib.rs:4:5
  |     [... inside N additional calls to `f::<i32>` ...]
  |     inside `X` at src/lib.rs:7:15
...
7 | const X: () = f(1);
  | -------------------
  |
  = note: `#[deny(const_err)]` on by default
  = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
  = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>

@rustbot modify labels: +A-const-fn +D-verbose
@PatchMixolydic PatchMixolydic added A-diagnostics Area: Messages for errors, warnings, and lints T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Jan 11, 2022
@rustbot rustbot added A-const-fn Area: const fn foo(..) {..}. Pure functions which can be applied at compile time. D-verbose Diagnostics: Too much output caused by a single piece of incorrect code. labels Jan 11, 2022
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@compiler-errors compiler-errors mentioned this issue Jan 12, 2022
Merged
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this issue Feb 3, 2022
@matthiaskrgr
Rollup merge of rust-lang#92802 - compiler-errors:deduplicate-stack-t…
a11629e 
…race, r=oli-obk

Deduplicate lines in long const-eval stack trace

Lemme know if this is kinda overkill, lol.

Fixes rust-lang#92796
@bors bors closed this as completed in 2fe9f76 Feb 3, 2022
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Deduplicate lines in long const-eval stack trace compiler-errors/rust
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