don't point at const usage site for resolution-time errors

also share the code that emits the actual error

Author: RalfJung

compiler/rustc_codegen_cranelift/src/base.rs

@@ -2,7 +2,6 @@
 
 use rustc_ast::InlineAsmOptions;
 use rustc_index::IndexVec;
-use rustc_middle::mir::interpret::ErrorHandled;
 use rustc_middle::ty::adjustment::PointerCoercion;
 use rustc_middle::ty::layout::FnAbiOf;
 use rustc_middle::ty::print::with_no_trimmed_paths;
@@ -251,21 +250,15 @@ pub(crate) fn verify_func(
 }
 
 fn codegen_fn_body(fx: &mut FunctionCx<'_, '_, '_>, start_block: Block) {
-    match fx.mir.post_mono_checks(fx.tcx, ty::ParamEnv::reveal_all(), |c| Ok(fx.monomorphize(c))) {
-        Ok(()) => {}
-        Err(ErrorHandled::TooGeneric(span)) => {
-            span_bug!(span, "codegen encountered polymorphic constant");
-        }
-        Err(ErrorHandled::Reported(info, span)) => {
-            if !info.is_tainted_by_errors() {
-                fx.tcx.sess.span_err(span, "erroneous constant encountered");
-            }
-            fx.bcx.append_block_params_for_function_params(fx.block_map[START_BLOCK]);
-            fx.bcx.switch_to_block(fx.block_map[START_BLOCK]);
-            // compilation should have been aborted
-            fx.bcx.ins().trap(TrapCode::UnreachableCodeReached);
-            return;
-        }
+    if let Err(err) =
+        fx.mir.post_mono_checks(fx.tcx, ty::ParamEnv::reveal_all(), |c| Ok(fx.monomorphize(c)))
+    {
+        err.emit_err(fx.tcx);
+        fx.bcx.append_block_params_for_function_params(fx.block_map[START_BLOCK]);
+        fx.bcx.switch_to_block(fx.block_map[START_BLOCK]);
+        // compilation should have been aborted
+        fx.bcx.ins().trap(TrapCode::UnreachableCodeReached);
+        return;
     }
 
     let arg_uninhabited = fx

compiler/rustc_codegen_ssa/messages.ftl

@@ -19,8 +19,6 @@ codegen_ssa_copy_path_buf = unable to copy {$source_file} to {$output_path}: {$e
 
 codegen_ssa_create_temp_dir = couldn't create a temp dir: {$error}
 
-codegen_ssa_erroneous_constant = erroneous constant encountered
-
 codegen_ssa_error_creating_remark_dir = failed to create remark directory: {$error}
 
 codegen_ssa_expected_coverage_symbol = expected `coverage(off)` or `coverage(on)`
@@ -174,8 +172,6 @@ codegen_ssa_no_natvis_directory = error enumerating natvis directory: {$error}
 
 codegen_ssa_option_gcc_only = option `-Z gcc-ld` is used even though linker flavor is not gcc
 
-codegen_ssa_polymorphic_constant_too_generic = codegen encountered polymorphic constant: TooGeneric
-
 codegen_ssa_processing_dymutil_failed = processing debug info with `dsymutil` failed: {$status}
     .note = {$output}
 

compiler/rustc_codegen_ssa/src/errors.rs

@@ -595,20 +595,6 @@ pub struct InvalidWindowsSubsystem {
     pub subsystem: Symbol,
 }
 
-#[derive(Diagnostic)]
-#[diag(codegen_ssa_erroneous_constant)]
-pub struct ErroneousConstant {
-    #[primary_span]
-    pub span: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(codegen_ssa_polymorphic_constant_too_generic)]
-pub struct PolymorphicConstantTooGeneric {
-    #[primary_span]
-    pub span: Span,
-}
-
 #[derive(Diagnostic)]
 #[diag(codegen_ssa_shuffle_indices_evaluation)]
 pub struct ShuffleIndicesEvaluation {

compiler/rustc_codegen_ssa/src/mir/mod.rs

@@ -1,10 +1,8 @@
 use crate::base;
-use crate::errors;
 use crate::traits::*;
 use rustc_index::bit_set::BitSet;
 use rustc_index::IndexVec;
 use rustc_middle::mir;
-use rustc_middle::mir::interpret::ErrorHandled;
 use rustc_middle::mir::traversal;
 use rustc_middle::mir::UnwindTerminateReason;
 use rustc_middle::ty::layout::{FnAbiOf, HasTyCtxt, TyAndLayout};
@@ -214,20 +212,14 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
     fx.per_local_var_debug_info = fx.compute_per_local_var_debug_info(&mut start_bx);
 
     // Rust post-monomorphization checks; we later rely on them.
-    match mir.post_mono_checks(cx.tcx(), ty::ParamEnv::reveal_all(), |c| Ok(fx.monomorphize(c))) {
-        Ok(()) => {}
-        Err(ErrorHandled::TooGeneric(span)) => {
-            cx.tcx().sess.diagnostic().emit_bug(errors::PolymorphicConstantTooGeneric { span });
-        }
-        Err(ErrorHandled::Reported(info, span)) => {
-            if !info.is_tainted_by_errors() {
-                cx.tcx().sess.emit_err(errors::ErroneousConstant { span });
-            }
-            // This IR shouldn't ever be emitted, but let's try to guard against any of this code
-            // ever running.
-            start_bx.abort();
-            return;
-        }
+    if let Err(err) =
+        mir.post_mono_checks(cx.tcx(), ty::ParamEnv::reveal_all(), |c| Ok(fx.monomorphize(c)))
+    {
+        err.emit_err(cx.tcx());
+        // This IR shouldn't ever be emitted, but let's try to guard against any of this code
+        // ever running.
+        start_bx.abort();
+        return;
     }
 
     let memory_locals = analyze::non_ssa_locals(&fx);

compiler/rustc_const_eval/messages.ftl

@@ -83,9 +83,6 @@ const_eval_dyn_call_vtable_mismatch =
 const_eval_dyn_star_call_vtable_mismatch =
     `dyn*` call on a pointer whose vtable does not match its type
 
-const_eval_erroneous_constant =
-    erroneous constant used
-
 const_eval_error = {$error_kind ->
     [static] could not evaluate static initializer
     [const] evaluation of constant value failed

compiler/rustc_const_eval/src/errors.rs

@@ -239,13 +239,6 @@ pub struct LongRunningWarn {
     pub item_span: Span,
 }
 
-#[derive(Diagnostic)]
-#[diag(const_eval_erroneous_constant)]
-pub(crate) struct ErroneousConstUsed {
-    #[primary_span]
-    pub span: Span,
-}
-
 #[derive(Subdiagnostic)]
 #[note(const_eval_non_const_impl)]
 pub(crate) struct NonConstImplNote {

compiler/rustc_const_eval/src/interpret/eval_context.rs

@@ -24,7 +24,7 @@ use super::{
     MemPlaceMeta, Memory, MemoryKind, OpTy, Operand, Place, PlaceTy, Pointer, PointerArithmetic,
     Projectable, Provenance, Scalar, StackPopJump,
 };
-use crate::errors::{self, ErroneousConstUsed};
+use crate::errors;
 use crate::util;
 use crate::{fluent_generated as fluent, ReportErrorExt};
 
@@ -1063,17 +1063,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
     ) -> Result<T, ErrorHandled> {
         // Use a precise span for better cycle errors.
         query(self.tcx.at(span.unwrap_or_else(|| self.cur_span()))).map_err(|err| {
-            match err {
-                ErrorHandled::Reported(err, reported_span) => {
-                    // We trust the provided span more than the one that came out of the query.
-                    let span = span.unwrap_or(reported_span);
-                    if !err.is_tainted_by_errors() {
-                        // To make it easier to figure out where this error comes from, also add a note at the current location.
-                        self.tcx.sess.emit_note(ErroneousConstUsed { span });
-                    }
-                }
-                ErrorHandled::TooGeneric(_) => {}
-            }
+            err.emit_note(*self.tcx);
             err
         })
     }

compiler/rustc_middle/messages.ftl

@@ -52,6 +52,8 @@ middle_drop_check_overflow =
     overflow while adding drop-check rules for {$ty}
     .note = overflowed on {$overflow_ty}
 
+middle_erroneous_constant = erroneous constant encountered
+
 middle_layout_references_error =
     the type has an unknown layout
 

compiler/rustc_middle/src/error.rs

@@ -144,5 +144,12 @@ pub struct UnsupportedFnAbi {
     pub abi: &'static str,
 }
 
+#[derive(Diagnostic)]
+#[diag(middle_erroneous_constant)]
+pub struct ErroneousConstant {
+    #[primary_span]
+    pub span: Span,
+}
+
 /// Used by `rustc_const_eval`
 pub use crate::fluent_generated::middle_adjust_for_foreign_abi_error;

compiler/rustc_middle/src/mir/interpret/error.rs

@@ -1,8 +1,9 @@
 use super::{AllocId, AllocRange, ConstAlloc, Pointer, Scalar};
 
+use crate::error;
 use crate::mir::interpret::ConstValue;
 use crate::query::TyCtxtAt;
-use crate::ty::{layout, tls, Ty, ValTree};
+use crate::ty::{layout, tls, Ty, TyCtxt, ValTree};
 
 use rustc_data_structures::sync::Lock;
 use rustc_errors::{
@@ -41,6 +42,32 @@ impl ErrorHandled {
             ErrorHandled::TooGeneric(_span) => ErrorHandled::TooGeneric(span),
         }
     }
+
+    pub fn emit_err(&self, tcx: TyCtxt<'_>) -> ErrorGuaranteed {
+        match self {
+            &ErrorHandled::Reported(err, span) => {
+                if !err.is_tainted_by_errors && !span.is_dummy() {
+                    tcx.sess.emit_err(error::ErroneousConstant { span });
+                }
+                err.error
+            }
+            &ErrorHandled::TooGeneric(span) => tcx.sess.delay_span_bug(
+                span,
+                "encountered TooGeneric error when monomorphic data was expected",
+            ),
+        }
+    }
+
+    pub fn emit_note(&self, tcx: TyCtxt<'_>) {
+        match self {
+            &ErrorHandled::Reported(err, span) => {
+                if !err.is_tainted_by_errors && !span.is_dummy() {
+                    tcx.sess.emit_note(error::ErroneousConstant { span });
+                }
+            }
+            &ErrorHandled::TooGeneric(_) => {}
+        }
+    }
 }
 
 #[derive(Debug, Copy, Clone, PartialEq, Eq, HashStable, TyEncodable, TyDecodable)]
@@ -54,12 +81,6 @@ impl ReportedErrorInfo {
     pub fn tainted_by_errors(error: ErrorGuaranteed) -> ReportedErrorInfo {
         ReportedErrorInfo { is_tainted_by_errors: true, error }
     }
-
-    /// Returns true if evaluation failed because MIR was tainted by errors.
-    #[inline]
-    pub fn is_tainted_by_errors(self) -> bool {
-        self.is_tainted_by_errors
-    }
 }
 
 impl From<ErrorGuaranteed> for ReportedErrorInfo {

compiler/rustc_middle/src/mir/interpret/queries.rs

@@ -61,8 +61,10 @@ impl<'tcx> TyCtxt<'tcx> {
                 let cid = GlobalId { instance, promoted: ct.promoted };
                 self.const_eval_global_id(param_env, cid, span)
             }
-            Ok(None) => Err(ErrorHandled::TooGeneric(span.unwrap_or(DUMMY_SP))),
-            Err(err) => Err(ErrorHandled::Reported(err.into(), span.unwrap_or(DUMMY_SP))),
+            // For errors during resolution, we deliberately do not point at the usage site of the constant,
+            // since for these errors the place the constant is used shouldn't matter.
+            Ok(None) => Err(ErrorHandled::TooGeneric(DUMMY_SP)),
+            Err(err) => Err(ErrorHandled::Reported(err.into(), DUMMY_SP)),
         }
     }
 
@@ -117,8 +119,10 @@ impl<'tcx> TyCtxt<'tcx> {
                     }
                 })
             }
-            Ok(None) => Err(ErrorHandled::TooGeneric(span.unwrap_or(DUMMY_SP))),
-            Err(err) => Err(ErrorHandled::Reported(err.into(), span.unwrap_or(DUMMY_SP))),
+            // For errors during resolution, we deliberately do not point at the usage site of the constant,
+            // since for these errors the place the constant is used shouldn't matter.
+            Ok(None) => Err(ErrorHandled::TooGeneric(DUMMY_SP)),
+            Err(err) => Err(ErrorHandled::Reported(err.into(), DUMMY_SP)),
         }
     }
 
@@ -143,7 +147,8 @@ impl<'tcx> TyCtxt<'tcx> {
         // improve caching of queries.
         let inputs = self.erase_regions(param_env.and(cid));
         if let Some(span) = span {
-            self.at(span).eval_to_const_value_raw(inputs)
+            // The query doesn't know where it is being invoked, so we need to fix the span.
+            self.at(span).eval_to_const_value_raw(inputs).map_err(|e| e.with_span(span))
         } else {
             self.eval_to_const_value_raw(inputs)
         }
@@ -162,7 +167,8 @@ impl<'tcx> TyCtxt<'tcx> {
         let inputs = self.erase_regions(param_env.and(cid));
         debug!(?inputs);
         if let Some(span) = span {
-            self.at(span).eval_to_valtree(inputs)
+            // The query doesn't know where it is being invoked, so we need to fix the span.
+            self.at(span).eval_to_valtree(inputs).map_err(|e| e.with_span(span))
         } else {
             self.eval_to_valtree(inputs)
         }

compiler/rustc_middle/src/mir/mod.rs

@@ -588,10 +588,7 @@ impl<'tcx> Body<'tcx> {
         // the body successfully evaluate.
         for &const_ in &self.required_consts {
             let c = normalize_const(const_.literal)?;
-            c.eval(tcx, param_env, Some(const_.span)).map_err(|e| {
-                // The query results don't always have the span we want.
-                e.with_span(const_.span)
-            })?;
+            c.eval(tcx, param_env, Some(const_.span))?;
         }
 
         Ok(())

src/tools/clippy/tests/ui-toml/suppress_lint_in_const/test.stderr

@@ -4,7 +4,7 @@ error[E0080]: evaluation of `main::{constant#3}` failed
 LL |     const { &ARR[idx4()] }; // Ok, should not produce stderr, since `suppress-restriction-lint-in-const` is set true.
    |              ^^^^^^^^^^^ index out of bounds: the length is 2 but the index is 4
 
-note: erroneous constant used
+note: erroneous constant encountered
   --> $DIR/test.rs:37:5
    |
 LL |     const { &ARR[idx4()] }; // Ok, should not produce stderr, since `suppress-restriction-lint-in-const` is set true.

src/tools/clippy/tests/ui/indexing_slicing_index.stderr

@@ -24,7 +24,7 @@ error[E0080]: evaluation of `main::{constant#3}` failed
 LL |     const { &ARR[idx4()] };
    |              ^^^^^^^^^^^ index out of bounds: the length is 2 but the index is 4
 
-note: erroneous constant used
+note: erroneous constant encountered
   --> $DIR/indexing_slicing_index.rs:48:5
    |
 LL |     const { &ARR[idx4()] };

src/tools/miri/tests/fail/const-ub-checks.stderr

@@ -4,7 +4,7 @@ error[E0080]: evaluation of constant value failed
 LL |     ptr.read();
    |     ^^^^^^^^^^ accessing memory with alignment ALIGN, but alignment ALIGN is required
 
-note: erroneous constant used
+note: erroneous constant encountered
   --> $DIR/const-ub-checks.rs:LL:CC
    |
 LL |     let _x = UNALIGNED_READ;

src/tools/miri/tests/fail/erroneous_const.stderr

@@ -6,7 +6,7 @@ LL |     const VOID: ! = panic!();
    |
    = note: this error originates in the macro `$crate::panic::panic_2021` which comes from the expansion of the macro `panic` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-note: erroneous constant used
+note: erroneous constant encountered
   --> $DIR/erroneous_const.rs:LL:CC
    |
 LL |         let _ = PrintName::<T>::VOID;

src/tools/miri/tests/fail/erroneous_const2.stderr

@@ -4,13 +4,13 @@ error[E0080]: evaluation of constant value failed
 LL | const FOO: u32 = [X - Y, Y - X][(X < Y) as usize];
    |                   ^^^^^ attempt to compute `5_u32 - 6_u32`, which would overflow
 
-note: erroneous constant used
+note: erroneous constant encountered
   --> $DIR/erroneous_const2.rs:LL:CC
    |
 LL |     println!("{}", FOO);
    |                    ^^^
 
-note: erroneous constant used
+note: erroneous constant encountered
   --> $DIR/erroneous_const2.rs:LL:CC
    |
 LL |     println!("{}", FOO);

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

@@ -4,21 +4,21 @@ error[E0080]: evaluation of `<() as Tr>::B` failed
 LL |     const B: u8 = Self::A + 1;
    |                   ^^^^^^^^^^^ attempt to compute `u8::MAX + 1_u8`, which would overflow
 
-note: erroneous constant used
+note: erroneous constant encountered
   --> $DIR/defaults-not-assumed-fail.rs:33:16
    |
 LL |     assert_eq!(<() as Tr>::B, 0);    // causes the error above
    |                ^^^^^^^^^^^^^
 
-note: erroneous constant used
+note: erroneous constant encountered
   --> $DIR/defaults-not-assumed-fail.rs:33:5
    |
 LL |     assert_eq!(<() as Tr>::B, 0);    // causes the error above
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: this note originates in the macro `assert_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-note: erroneous constant used
+note: erroneous constant encountered
   --> $DIR/defaults-not-assumed-fail.rs:33:5
    |
 LL |     assert_eq!(<() as Tr>::B, 0);    // causes the error above

tests/ui/borrowck/issue-81899.stderr

@@ -16,7 +16,7 @@ LL | const _CONST: &[u8] = &f(&[], |_| {});
    |                        ^^^^^^^^^^^^^^
    = note: this error originates in the macro `$crate::panic::panic_2015` which comes from the expansion of the macro `panic` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-note: erroneous constant used
+note: erroneous constant encountered
   --> $DIR/issue-81899.rs:4:23
    |
 LL | const _CONST: &[u8] = &f(&[], |_| {});