Auto merge of rust-lang#119432 - gurry:117949-make-lint-run-on-promoteds, r=oli-obk

Make `ConstPropLint` lint run on promoteds

Fixes rust-lang#117949 wherein the lint didn't fire for the following promoteds:

- SHL or SHR operators in a non-optimized build
- any arithmetic operator in an optimized build

What I have done here is simply enabled `ConstPropLint` to run on promoted bodies by removing the relevant `if` check.

After this change _all_ promoted arithmetic operators will lint _in both non-optimized and optimized builds_. On the flip side programs containing the above mentioned overflowing promoteds that were accepted earlier will now be rejected. Hope that is okay from a backward compatibility standpoint.

I have added tests covering all overflowing promoted & non-promoted ops for both compile-time and runtime operations and for optimized as well as non-optimized builds.

I had to amend some existing tests to make them pass and had to delete a couple that were set to pass despite overflows.

This PR increases the number of duplicate diagnostics emitted (because the same operator might get linted in both the promoted MIR and the main MIR). I hope that is an acceptable trade-off given that we now lint overflows much more comprehensively than earlier.

Author: bors

compiler/rustc_mir_transform/src/const_prop_lint.rs

@@ -32,11 +32,6 @@ impl<'tcx> MirLint<'tcx> for ConstPropLint {
             return;
         }
 
-        // will be evaluated by miri and produce its errors there
-        if body.source.promoted.is_some() {
-            return;
-        }
-
         let def_id = body.source.def_id().expect_local();
         let def_kind = tcx.def_kind(def_id);
         let is_fn_like = def_kind.is_fn_like();

src/tools/miri/tests/pass/overflow_checks_off.rs

@@ -1,12 +1,17 @@
 //@compile-flags: -C overflow-checks=off
 
 // Check that we correctly implement the intended behavior of these operators
-// when they are not being overflow-checked.
+// when they are not being overflow-checked at runtime.
 
 // FIXME: if we call the functions in `std::ops`, we still get the panics.
 // Miri does not implement the codegen-time hack that backs `#[rustc_inherit_overflow_checks]`.
 // use std::ops::*;
 
+
+// Disable _compile-time_ overflow linting
+// so that we can test runtime overflow checks
+ #![allow(arithmetic_overflow)]
+
 fn main() {
     assert_eq!(-{ -0x80i8 }, -0x80);
 

tests/ui/associated-consts/defaults-cyclic-fail.stderr

@@ -20,7 +20,7 @@ note: ...which requires const-evaluating + checking `Tr::B`...
 LL |     const B: u8 = Self::A;
    |                   ^^^^^^^
    = note: ...which again requires simplifying constant for the type system `Tr::A`, completing the cycle
-note: cycle used when const-evaluating + checking `main::promoted[1]`
+note: cycle used when optimizing promoted MIR for `main`
   --> $DIR/defaults-cyclic-fail.rs:16:16
    |
 LL |     assert_eq!(<() as Tr>::A, 0);

tests/ui/associated-consts/defaults-not-assumed-fail.stderr

@@ -10,6 +10,14 @@ note: erroneous constant encountered
 LL |     assert_eq!(<() as Tr>::B, 0);    // causes the error above
    |                ^^^^^^^^^^^^^
 
+note: erroneous constant encountered
+  --> $DIR/defaults-not-assumed-fail.rs:33:16
+   |
+LL |     assert_eq!(<() as Tr>::B, 0);    // causes the error above
+   |                ^^^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+
 note: erroneous constant encountered
   --> $DIR/defaults-not-assumed-fail.rs:33:5
    |

tests/ui/consts/const-err2.noopt.stderr

@@ -10,6 +10,14 @@ note: erroneous constant encountered
 LL |     println!("{}", <Bar<u16, u8> as Foo>::AMT);
    |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
+note: erroneous constant encountered
+  --> $DIR/issue-44578.rs:25:20
+   |
+LL |     println!("{}", <Bar<u16, u8> as Foo>::AMT);
+   |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+
 note: erroneous constant encountered
   --> $DIR/issue-44578.rs:25:20
    |

tests/ui/consts/const-err2.opt.stderr

@@ -14,6 +14,7 @@ struct Sum<A, B>(A, B);
 impl<A: Unsigned, B: Unsigned> Unsigned for Sum<A, B> {
     const MAX: u8 = A::MAX + B::MAX;
     //~^ ERROR evaluation of `<Sum<U8, U8> as Unsigned>::MAX` failed
+    //~| ERROR evaluation of `<Sum<U8, U8> as Unsigned>::MAX` failed
 }
 
 fn foo<T>(_: T) -> &'static u8 {