Rollup merge of #85112 - RalfJung:promoted-errors, r=oli-obk

ensure failing promoteds in const/static bodies are handled correctly

`const`/`static` bodies are the one case where we still promote code that might fail to evaluate. Ensure that this is handled correctly; in particular, it must not fail compilation.

`src/test/ui/consts/const-eval/erroneous-const.rs` ensures that when a non-promoted fails to evaluate, we *do* show an error.

r? `@oli-obk`

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

@@ -10,6 +10,8 @@ impl<T> PrintName<T> {
 
 const fn no_codegen<T>() {
     if false {
+        // This bad constant is only used in dead code in a no-codegen function... and yet we still
+        // must make sure that the build fails.
         let _ = PrintName::<T>::VOID; //~ERROR could not evaluate static initializer
     }
 }

src/test/ui/consts/const-eval/erroneous-const.stderr

@@ -27,16 +27,16 @@ LL | #![warn(const_err, unconditional_panic)]
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
 error[E0080]: could not evaluate static initializer
-  --> $DIR/erroneous-const.rs:13:17
+  --> $DIR/erroneous-const.rs:15:17
    |
 LL |         let _ = PrintName::<T>::VOID;
    |                 ^^^^^^^^^^^^^^^^^^^^
    |                 |
    |                 referenced constant has errors
-   |                 inside `no_codegen::<i32>` at $DIR/erroneous-const.rs:13:17
+   |                 inside `no_codegen::<i32>` at $DIR/erroneous-const.rs:15:17
 ...
 LL | pub static FOO: () = no_codegen::<i32>();
-   |                      ------------------- inside `FOO` at $DIR/erroneous-const.rs:17:22
+   |                      ------------------- inside `FOO` at $DIR/erroneous-const.rs:19:22
 
 error: aborting due to previous error; 2 warnings emitted
 

src/test/ui/consts/const-eval/erroneous-const2.rs

+//! Make sure we error on erroneous consts even if they are unused.
+#![warn(const_err, unconditional_panic)]
+
+struct PrintName<T>(T);
+impl<T> PrintName<T> {
+    const VOID: () = [()][2]; //~WARN any use of this value will cause an error
+    //~^ WARN this operation will panic at runtime
+    //~| WARN this was previously accepted by the compiler but is being phased out
+}
+
+pub static FOO: () = {
+    if false {
+        // This bad constant is only used in dead code in a static initializer... and yet we still
+        // must make sure that the build fails.
+        let _ = PrintName::<i32>::VOID; //~ERROR could not evaluate static initializer
+    }
+};
+
+fn main() {
+    FOO
+}

src/test/ui/consts/const-eval/erroneous-const2.stderr

+warning: this operation will panic at runtime
+  --> $DIR/erroneous-const2.rs:6:22
+   |
+LL |     const VOID: () = [()][2];
+   |                      ^^^^^^^ index out of bounds: the length is 1 but the index is 2
+   |
+note: the lint level is defined here
+  --> $DIR/erroneous-const2.rs:2:20
+   |
+LL | #![warn(const_err, unconditional_panic)]
+   |                    ^^^^^^^^^^^^^^^^^^^
+
+warning: any use of this value will cause an error
+  --> $DIR/erroneous-const2.rs:6:22
+   |
+LL |     const VOID: () = [()][2];
+   |     -----------------^^^^^^^-
+   |                      |
+   |                      index out of bounds: the length is 1 but the index is 2
+   |
+note: the lint level is defined here
+  --> $DIR/erroneous-const2.rs:2:9
+   |
+LL | #![warn(const_err, 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>
+
+error[E0080]: could not evaluate static initializer
+  --> $DIR/erroneous-const2.rs:15:17
+   |
+LL |         let _ = PrintName::<i32>::VOID;
+   |                 ^^^^^^^^^^^^^^^^^^^^^^ referenced constant has errors
+
+error: aborting due to previous error; 2 warnings emitted
+
+For more information about this error, try `rustc --explain E0080`.

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

 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();
@@ -18,7 +18,7 @@ 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)]
    |         ^^^^^^^^^
@@ -26,7 +26,7 @@ LL | #![warn(const_err, arithmetic_overflow, unconditional_panic)]
    = 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

 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();
@@ -18,7 +18,7 @@ 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)]
    |         ^^^^^^^^^
@@ -26,7 +26,7 @@ LL | #![warn(const_err, arithmetic_overflow, unconditional_panic)]
    = 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

 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();
@@ -18,7 +18,7 @@ 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)]
    |         ^^^^^^^^^
@@ -26,7 +26,7 @@ LL | #![warn(const_err, arithmetic_overflow, unconditional_panic)]
    = 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 fn oob() -> i32 {
     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;
+}