Rollup merge of #111096 - AngelicosPhosphoros:overflow_checks_issue_91130, r=petrochenkov

Add support for `cfg(overflow_checks)`

This PR adds support for detecting if overflow checks are enabled in similar fashion as `debug_assertions` are detected. Possible use-case of this, for example, if we want to use checked integer casts in builds with overflow checks, e.g.

```rust
pub fn cast(val: usize)->u16 {
    if cfg!(overflow_checks) {
        val.try_into().unwrap()
    }
    else{
        vas as _
    }
}
```

Resolves #91130.

4 files changed, 56 insertions, 0 deletions

diff --git a/tests/ui/feature-gates/feature-gate-cfg_overflow_checks.rs b/tests/ui/feature-gates/feature-gate-cfg_overflow_checks.rs
new file mode 100644
index 00000000000..cb265aa7f25
--- /dev/null
+++ b/tests/ui/feature-gates/feature-gate-cfg_overflow_checks.rs
@@ -0,0 +1,6 @@
+#![crate_type = "lib"]
+
+#[cfg(overflow_checks)] //~ ERROR `cfg(overflow_checks)` is experimental
+pub fn cast(v: i64)->u32{
+    todo!()
+}
diff --git a/tests/ui/feature-gates/feature-gate-cfg_overflow_checks.stderr b/tests/ui/feature-gates/feature-gate-cfg_overflow_checks.stderr
new file mode 100644
index 00000000000..79aba7945f6
--- /dev/null
+++ b/tests/ui/feature-gates/feature-gate-cfg_overflow_checks.stderr
@@ -0,0 +1,12 @@
+error[E0658]: `cfg(overflow_checks)` is experimental and subject to change
+  --> $DIR/feature-gate-cfg_overflow_checks.rs:3:7
+   |
+LL | #[cfg(overflow_checks)]
+   |       ^^^^^^^^^^^^^^^
+   |
+   = note: see issue #111466 <https://github.com/rust-lang/rust/issues/111466> for more information
+   = help: add `#![feature(cfg_overflow_checks)]` to the crate attributes to enable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0658`.
diff --git a/tests/ui/numbers-arithmetic/overflow-attribute-works-1.rs b/tests/ui/numbers-arithmetic/overflow-attribute-works-1.rs
new file mode 100644
index 00000000000..318be2a6401
--- /dev/null
+++ b/tests/ui/numbers-arithmetic/overflow-attribute-works-1.rs
@@ -0,0 +1,19 @@
+// run-pass
+// compile-flags: -C overflow_checks=true
+
+#![feature(cfg_overflow_checks)]
+
+fn main() {
+    assert!(cfg!(overflow_checks));
+    assert!(compiles_differently());
+}
+
+#[cfg(overflow_checks)]
+fn compiles_differently()->bool {
+    true
+}
+
+#[cfg(not(overflow_checks))]
+fn compiles_differently()->bool {
+    false
+}
diff --git a/tests/ui/numbers-arithmetic/overflow-attribute-works-2.rs b/tests/ui/numbers-arithmetic/overflow-attribute-works-2.rs
new file mode 100644
index 00000000000..0367d980a64
--- /dev/null
+++ b/tests/ui/numbers-arithmetic/overflow-attribute-works-2.rs
@@ -0,0 +1,19 @@
+// run-pass
+// compile-flags: -C overflow_checks=false
+
+#![feature(cfg_overflow_checks)]
+
+fn main() {
+    assert!(!cfg!(overflow_checks));
+    assert!(!compiles_differently());
+}
+
+#[cfg(overflow_checks)]
+fn compiles_differently()->bool {
+    true
+}
+
+#[cfg(not(overflow_checks))]
+fn compiles_differently()->bool {
+    false
+}