don't evaluate constants if borrowck fails

compiler/rustc_middle/src/mir/query.rs

@@ -214,6 +214,7 @@ pub struct BorrowCheckResult<'tcx> {
     pub concrete_opaque_types: VecMap<OpaqueTypeKey<'tcx>, Ty<'tcx>>,
     pub closure_requirements: Option<ClosureRegionRequirements<'tcx>>,
     pub used_mut_upvars: SmallVec<[Field; 8]>,
+    pub errored: bool,
 }
 
 /// The result of the `mir_const_qualif` query.

compiler/rustc_mir/src/borrow_check/mod.rs

@@ -432,10 +432,12 @@ fn do_mir_borrowck<'a, 'tcx>(
         diag.buffer(&mut mbcx.errors_buffer);
     }
 
+    let mut errored = false;
     if !mbcx.errors_buffer.is_empty() {
         mbcx.errors_buffer.sort_by_key(|diag| diag.sort_span);
 
         for diag in mbcx.errors_buffer.drain(..) {
+            errored |= diag.is_error();
             mbcx.infcx.tcx.sess.diagnostic().emit_diagnostic(&diag);
         }
     }
@@ -444,6 +446,7 @@ fn do_mir_borrowck<'a, 'tcx>(
         concrete_opaque_types: opaque_type_values,
         closure_requirements: opt_closure_req,
         used_mut_upvars: mbcx.used_mut_upvars,
+        errored,
     };
 
     debug!("do_mir_borrowck: result = {:#?}", result);

compiler/rustc_mir/src/const_eval/eval_queries.rs

@@ -276,6 +276,8 @@ pub fn eval_to_allocation_raw_provider<'tcx>(
     let cid = key.value;
     let def = cid.instance.def.with_opt_param();
 
+    debug!("promoted={:?}", cid.promoted);
+
     if let Some(def) = def.as_local() {
         if tcx.has_typeck_results(def.did) {
             if let Some(error_reported) = tcx.typeck_opt_const_arg(def).tainted_by_errors {
@@ -292,6 +294,18 @@ pub fn eval_to_allocation_raw_provider<'tcx>(
         if let Some(error_reported) = tcx.mir_const_qualif_opt_const_arg(def).error_occured {
             return Err(ErrorHandled::Reported(error_reported));
         }
+
+        if cid.promoted.is_none() {
+            let borrowck_results = if let Some(param_did) = def.const_param_did {
+                tcx.mir_borrowck_const_arg((def.did, param_did))
+            } else {
+                tcx.mir_borrowck(def.did)
+            };
+
+            if borrowck_results.errored {
+                return Err(ErrorHandled::Reported(ErrorReported {}));
+            }
+        }
     }
 
     let is_static = tcx.is_static(def.did);

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

@@ -0,0 +1,9 @@
+struct Bug {
+    A: [(); {
+        let x;
+        x
+        //~^ error: use of possibly-uninitialized variable
+    }],
+}
+
+fn main() {}

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

@@ -0,0 +1,9 @@
+error[E0381]: use of possibly-uninitialized variable: `x`
+  --> $DIR/borrowck_error_no_ice.rs:4:9
+   |
+LL |         x
+   |         ^ use of possibly-uninitialized `x`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0381`.

src/test/ui/consts/const-mut-refs/issue-76510.32bit.stderr

@@ -19,18 +19,7 @@ error[E0596]: cannot borrow data in a `&` reference as mutable
 LL | const S: &'static mut str = &mut " hello ";
    |                             ^^^^^^^^^^^^^^ cannot borrow as mutable
 
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/issue-76510.rs:5:1
-   |
-LL | const S: &'static mut str = &mut " hello ";
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered mutable reference in a `const`
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 8, align: 4) {
-               ╾─alloc2──╼ 07 00 00 00                         │ ╾──╼....
-           }
-
-error: aborting due to 4 previous errors
+error: aborting due to 3 previous errors
 
-Some errors have detailed explanations: E0080, E0596, E0658, E0764.
-For more information about an error, try `rustc --explain E0080`.
+Some errors have detailed explanations: E0596, E0658, E0764.
+For more information about an error, try `rustc --explain E0596`.

src/test/ui/consts/const-mut-refs/issue-76510.64bit.stderr

@@ -19,18 +19,7 @@ error[E0596]: cannot borrow data in a `&` reference as mutable
 LL | const S: &'static mut str = &mut " hello ";
    |                             ^^^^^^^^^^^^^^ cannot borrow as mutable
 
-error[E0080]: it is undefined behavior to use this value
-  --> $DIR/issue-76510.rs:5:1
-   |
-LL | const S: &'static mut str = &mut " hello ";
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered mutable reference in a `const`
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 16, align: 8) {
-               ╾───────alloc2────────╼ 07 00 00 00 00 00 00 00 │ ╾──────╼........
-           }
-
-error: aborting due to 4 previous errors
+error: aborting due to 3 previous errors
 
-Some errors have detailed explanations: E0080, E0596, E0658, E0764.
-For more information about an error, try `rustc --explain E0080`.
+Some errors have detailed explanations: E0596, E0658, E0764.
+For more information about an error, try `rustc --explain E0596`.

src/test/ui/consts/const-mut-refs/issue-76510.rs

@@ -6,12 +6,11 @@ const S: &'static mut str = &mut " hello ";
 //~^ ERROR: mutable references are not allowed in the final value of constants
 //~| ERROR: mutation through a reference is not allowed in constants
 //~| ERROR: cannot borrow data in a `&` reference as mutable
-//~| ERROR: it is undefined behavior to use this value
 
 const fn trigger() -> [(); unsafe {
-        let s = transmute::<(*const u8, usize), &ManuallyDrop<str>>((S.as_ptr(), 3));
-        0
-    }] {
+    let s = transmute::<(*const u8, usize), &ManuallyDrop<str>>((S.as_ptr(), 3));
+    0
+}] {
     [(); 0]
 }
 

src/test/ui/consts/issue-78655.rs

@@ -1,4 +1,4 @@
-const FOO: *const u32 = { //~ ERROR encountered dangling pointer in final constant
+const FOO: *const u32 = {
     let x;
     &x //~ ERROR borrow of possibly-uninitialized variable: `x`
 };

src/test/ui/consts/issue-78655.stderr

@@ -4,15 +4,6 @@ error[E0381]: borrow of possibly-uninitialized variable: `x`
 LL |     &x
    |     ^^ use of possibly-uninitialized `x`
 
-error: encountered dangling pointer in final constant
-  --> $DIR/issue-78655.rs:1:1
-   |
-LL | / const FOO: *const u32 = {
-LL | |     let x;
-LL | |     &x
-LL | | };
-   | |__^
-
 error: could not evaluate constant pattern
   --> $DIR/issue-78655.rs:7:9
    |
@@ -25,6 +16,6 @@ error: could not evaluate constant pattern
 LL |     let FOO = FOO;
    |         ^^^
 
-error: aborting due to 4 previous errors
+error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0381`.