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rust-bors merged 1 commit into from
Sep 11, 2026
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doc: replace exceeding_bitshifts with arithmetic_overflow #162273

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22 changes: 8 additions & 14 deletions src/doc/rustc/src/lints/levels.md
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Original file line number Diff line number Diff line change
Expand Up @@ -104,7 +104,7 @@ level is capped via cap-lints.
## deny

A 'deny' lint produces an error if you violate it. For example, this code
runs into the `exceeding_bitshifts` lint.
runs into the `arithmetic_overflow` lint.

```rust,no_run
fn main() {
Expand All @@ -114,13 +114,13 @@ fn main() {

```bash
$ rustc main.rs
error: bitshift exceeds the type's number of bits
--> main.rs:2:13
error: this arithmetic operation will overflow
--> main.rs:2:5
|
2 | 100u8 << 10;
| ^^^^^^^^^^^
| ^^^^^^^^^^^ attempt to shift left by `10_i32`, which would overflow
|
= note: `#[deny(exceeding_bitshifts)]` on by default
= note: `#[deny(arithmetic_overflow)]` on by default
```

What's the difference between an error from a lint and a regular old error?
Expand Down Expand Up @@ -306,19 +306,13 @@ And we compile it, capping lints to warn:

```bash
$ rustc lib.rs --cap-lints warn
warning: bitshift exceeds the type's number of bits
warning: this arithmetic operation will overflow
--> lib.rs:2:5
|
2 | 100u8 << 10;
| ^^^^^^^^^^^
| ^^^^^^^^^^^ attempt to shift left by `10_i32`, which would overflow
|
= note: `#[warn(exceeding_bitshifts)]` on by default

warning: this expression will panic at run-time
--> lib.rs:2:5
|
2 | 100u8 << 10;
| ^^^^^^^^^^^ attempt to shift left with overflow
= note: `#[warn(arithmetic_overflow)]` on by default

@Enselic Enselic Sep 8, 2026

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When I run this locally it says deny and not warn. Does it say warn when you run locally?

Suggested change
= note: `#[warn(arithmetic_overflow)]` on by default
= note: `#[deny(arithmetic_overflow)]` on by default
my output 
$ git diff
diff --git a/src/doc/rustc/src/lints/levels.md b/src/doc/rustc/src/lints/levels.md
index 5b23ac9e09c..2274b70c509 100644
--- a/src/doc/rustc/src/lints/levels.md
+++ b/src/doc/rustc/src/lints/levels.md
@@ -106,7 +106,7 @@ level is capped via cap-lints.
 A 'deny' lint produces an error if you violate it. For example, this code
 runs into the `exceeding_bitshifts` lint.

-```rust,no_run
+```rust
 fn main() {
     100u8 << 10;
 }
@@ -296,7 +296,7 @@ pub fn get_path() -> PathBuf {
 This is the maximum level for all lints. So for example, if we take our
 code sample from the "deny" lint level above:

-```rust,no_run
+```rust
 fn main() {
     100u8 << 10;
 }
$ ./x test src/doc/rustc -- src/lints/levels.md
Building bootstrap
    Finished `dev` profile [unoptimized] target(s) in 0.06s
/home/martin/src/rust/build/x86_64-unknown-linux-gnu/ci-llvm/bin/llvm-strip does not exist; skipping copy
Building stage1 compiler artifacts (stage0 -> stage1, x86_64-unknown-linux-gnu)
    Finished `release` profile [optimized + debuginfo] target(s) in 0.21s
Creating a sysroot for stage1 compiler (use `rustup toolchain link 'name' build/host/stage1`)
Building stage1 lld-wrapper (stage0 -> stage1, x86_64-unknown-linux-gnu)
    Finished `release` profile [optimized + debuginfo] target(s) in 0.08s
Building stage1 library artifacts (stage1 -> stage1, x86_64-unknown-linux-gnu)
    Finished `dist` profile [optimized + debuginfo] target(s) in 0.03s
Testing stage1 book rustc (x86_64-unknown-linux-gnu)
Building stage1 rustdoc_tool_binary (stage0 -> stage1, x86_64-unknown-linux-gnu)
    Finished `release` profile [optimized + debuginfo] target(s) in 0.13s
Command `/home/martin/src/rust/build/bootstrap/debug/rustdoc -Wrustdoc::invalid_codeblock_attributes -Znormalize-docs -Z unstable-options --test /home/martin/src/rust/src/doc/rustc/src/lints/levels.md --test-args src/lints/levels.md` failed with exit code 101
Created at: src/bootstrap/src/core/builder/mod.rs:1524:23
Executed at: src/bootstrap/src/core/build_steps/test.rs:3178:13

--- STDOUT vvv
running 12 tests
test /home/martin/src/rust/src/doc/rustc/src/lints/levels.md - Lint_Levels::Priority_of_lint_level_sources (line 370) - compile fail ... ok
test /home/martin/src/rust/src/doc/rustc/src/lints/levels.md - Lint_Levels::Priority_of_lint_level_sources (line 346) - compile fail ... ok
test /home/martin/src/rust/src/doc/rustc/src/lints/levels.md - Lint_Levels::deny (line 109) ... FAILED
test /home/martin/src/rust/src/doc/rustc/src/lints/levels.md - Lint_Levels::Configuring_warning_levels::Capping_lints (line 299) ... FAILED
test /home/martin/src/rust/src/doc/rustc/src/lints/levels.md - Lint_Levels::Configuring_warning_levels::Via_an_attribute (line 263) ... ok
test /home/martin/src/rust/src/doc/rustc/src/lints/levels.md - Lint_Levels::Priority_of_lint_level_sources (line 400) ... ok
test /home/martin/src/rust/src/doc/rustc/src/lints/levels.md - Lint_Levels::warn (line 76) ... ok
test /home/martin/src/rust/src/doc/rustc/src/lints/levels.md - Lint_Levels::allow (line 21) ... ok
test /home/martin/src/rust/src/doc/rustc/src/lints/levels.md - Lint_Levels::Priority_of_lint_level_sources (line 423) ... ok
test /home/martin/src/rust/src/doc/rustc/src/lints/levels.md - Lint_Levels::Configuring_warning_levels::Via_an_attribute (line 271) ... ok
test /home/martin/src/rust/src/doc/rustc/src/lints/levels.md - Lint_Levels::Configuring_warning_levels::Via_an_attribute (line 282) ... ok
test /home/martin/src/rust/src/doc/rustc/src/lints/levels.md - Lint_Levels::expect (line 45) ... ok

failures:

---- /home/martin/src/rust/src/doc/rustc/src/lints/levels.md - Lint_Levels::deny (line 109) stdout ----
error: this arithmetic operation will overflow
   --> /home/martin/src/rust/src/doc/rustc/src/lints/levels.md:111:5
    |
111 |     100u8 << 10;
    |     ^^^^^^^^^^^ attempt to shift left by `10_i32`, which would overflow
    |
    = note: `#[deny(arithmetic_overflow)]` on by default

error: aborting due to 1 previous error

Couldn't compile the test.
---- /home/martin/src/rust/src/doc/rustc/src/lints/levels.md - Lint_Levels::Configuring_warning_levels::Capping_lints (line 299) stdout ----
error: this arithmetic operation will overflow
   --> /home/martin/src/rust/src/doc/rustc/src/lints/levels.md:301:5
    |
301 |     100u8 << 10;
    |     ^^^^^^^^^^^ attempt to shift left by `10_i32`, which would overflow
    |
    = note: `#[deny(arithmetic_overflow)]` on by default

error: aborting due to 1 previous error

Couldn't compile the test.

failures:
    /home/martin/src/rust/src/doc/rustc/src/lints/levels.md - Lint_Levels::Configuring_warning_levels::Capping_lints (line 299)
    /home/martin/src/rust/src/doc/rustc/src/lints/levels.md - Lint_Levels::deny (line 109)

test result: FAILED. 10 passed; 2 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.16s

--- STDERR vvv


Command has failed. Rerun with -v to see more details.
Build completed unsuccessfully in 0:00:01

@chiang03 chiang03 Sep 9, 2026

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this section is "Capping lints", the command above is rustc lib.rs --cap-lints warn

@Enselic Enselic Sep 10, 2026

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Ah, right, that flag is not passed when rustdoc runs the test, of course. This confirms it says warn:

echo 'fn main() { 100u8 << 10; }' | rustc --cap-lints warn -

All good then.

```

It now only warns, rather than errors. We can go further and allow all lints:
Expand Down
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