ensure failing promoteds in const/static bodies are handled correctly

Author: RalfJung

src/test/ui/consts/const-eval/promoted_errors.noopt.stderr

@@ -1,12 +1,12 @@
 warning: any use of this value will cause an error
-  --> $DIR/promoted_errors.rs:13:5
+  --> $DIR/promoted_errors.rs:15:5
    |
 LL |       0 - 1
    |       ^^^^^
    |       |
    |       attempt to compute `0_u32 - 1_u32`, which would overflow
-   |       inside `overflow` at $DIR/promoted_errors.rs:13:5
-   |       inside `X` at $DIR/promoted_errors.rs:33:29
+   |       inside `overflow` at $DIR/promoted_errors.rs:15:5
+   |       inside `X` at $DIR/promoted_errors.rs:38:29
 ...
 LL | / const X: () = {
 LL | |     let _x: &'static u32 = &overflow();
@@ -18,15 +18,15 @@ LL | | };
    | |__-
    |
 note: the lint level is defined here
-  --> $DIR/promoted_errors.rs:9:9
+  --> $DIR/promoted_errors.rs:11:9
    |
 LL | #![warn(const_err, arithmetic_overflow, unconditional_panic)]
    |         ^^^^^^^^^
    = 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>
 
 warning: any use of this value will cause an error
-  --> $DIR/promoted_errors.rs:33:28
+  --> $DIR/promoted_errors.rs:38:28
    |
 LL | / const X: () = {
 LL | |     let _x: &'static u32 = &overflow();

src/test/ui/consts/const-eval/promoted_errors.opt.stderr

@@ -1,12 +1,12 @@
 warning: any use of this value will cause an error
-  --> $DIR/promoted_errors.rs:18:5
+  --> $DIR/promoted_errors.rs:20:5
    |
 LL |       1 / 0
    |       ^^^^^
    |       |
    |       attempt to divide `1_i32` by zero
-   |       inside `div_by_zero1` at $DIR/promoted_errors.rs:18:5
-   |       inside `X` at $DIR/promoted_errors.rs:36:29
+   |       inside `div_by_zero1` at $DIR/promoted_errors.rs:20:5
+   |       inside `X` at $DIR/promoted_errors.rs:41:29
 ...
 LL | / const X: () = {
 LL | |     let _x: &'static u32 = &overflow();
@@ -18,15 +18,15 @@ LL | | };
    | |__-
    |
 note: the lint level is defined here
-  --> $DIR/promoted_errors.rs:9:9
+  --> $DIR/promoted_errors.rs:11:9
    |
 LL | #![warn(const_err, arithmetic_overflow, unconditional_panic)]
    |         ^^^^^^^^^
    = 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>
 
 warning: any use of this value will cause an error
-  --> $DIR/promoted_errors.rs:36:28
+  --> $DIR/promoted_errors.rs:41:28
    |
 LL | / const X: () = {
 LL | |     let _x: &'static u32 = &overflow();

src/test/ui/consts/const-eval/promoted_errors.opt_with_overflow_checks.stderr

@@ -1,12 +1,12 @@
 warning: any use of this value will cause an error
-  --> $DIR/promoted_errors.rs:13:5
+  --> $DIR/promoted_errors.rs:15:5
    |
 LL |       0 - 1
    |       ^^^^^
    |       |
    |       attempt to compute `0_u32 - 1_u32`, which would overflow
-   |       inside `overflow` at $DIR/promoted_errors.rs:13:5
-   |       inside `X` at $DIR/promoted_errors.rs:33:29
+   |       inside `overflow` at $DIR/promoted_errors.rs:15:5
+   |       inside `X` at $DIR/promoted_errors.rs:38:29
 ...
 LL | / const X: () = {
 LL | |     let _x: &'static u32 = &overflow();
@@ -18,15 +18,15 @@ LL | | };
    | |__-
    |
 note: the lint level is defined here
-  --> $DIR/promoted_errors.rs:9:9
+  --> $DIR/promoted_errors.rs:11:9
    |
 LL | #![warn(const_err, arithmetic_overflow, unconditional_panic)]
    |         ^^^^^^^^^
    = 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>
 
 warning: any use of this value will cause an error
-  --> $DIR/promoted_errors.rs:33:28
+  --> $DIR/promoted_errors.rs:38:28
    |
 LL | / const X: () = {
 LL | |     let _x: &'static u32 = &overflow();

src/test/ui/consts/const-eval/promoted_errors.rs

@@ -6,6 +6,8 @@
 // build-pass
 // ignore-pass (test emits codegen-time warnings and verifies that they are not errors)
 
+//! This test ensures that when we promote code that fails to evaluate, the build still succeeds.
+
 #![warn(const_err, arithmetic_overflow, unconditional_panic)]
 
 // The only way to have promoteds that fail is in `const fn` called from `const`/`static`.
@@ -29,6 +31,9 @@ const fn oob() -> i32 {
     [1, 2, 3][4]
 }
 
+// An unused constant containing failing promoteds.
+// This should work as long as `const_err` can be turned into just a warning;
+// once it turns into a hard error, just remove `X`.
 const X: () = {
     let _x: &'static u32 = &overflow();
     //[opt_with_overflow_checks,noopt]~^ WARN any use of this value will cause an error
@@ -41,4 +46,21 @@ const X: () = {
     let _x: &'static i32 = &oob();
 };
 
-fn main() {}
+const fn mk_false() -> bool { false }
+
+// An actually used constant referencing failing promoteds in dead code.
+// This needs to always work.
+const Y: () = {
+    if mk_false() {
+        let _x: &'static u32 = &overflow();
+        let _x: &'static i32 = &div_by_zero1();
+        let _x: &'static i32 = &div_by_zero2();
+        let _x: &'static i32 = &div_by_zero3();
+        let _x: &'static i32 = &oob();
+    }
+    ()
+};
+
+fn main() {
+    let _y = Y;
+}