const-eval: make lint scope computation consistent

Author: RalfJung

compiler/rustc_const_eval/src/const_eval/error.rs

@@ -1,7 +1,6 @@
 use std::mem;
 
 use rustc_errors::{DiagArgName, DiagArgValue, DiagMessage, Diagnostic, IntoDiagArg};
-use rustc_hir::CRATE_HIR_ID;
 use rustc_middle::mir::interpret::{Provenance, ReportedErrorInfo};
 use rustc_middle::mir::AssertKind;
 use rustc_middle::query::TyCtxtAt;
@@ -156,7 +155,7 @@ where
     }
 }
 
-/// Emit a lint from a const-eval situation.
+/// Emit a lint from a const-eval situation, with a backtrace.
 // Even if this is unused, please don't remove it -- chances are we will need to emit a lint during const-eval again in the future!
 pub(super) fn lint<'tcx, L>(
     tcx: TyCtxtAt<'tcx>,
@@ -168,12 +167,5 @@ pub(super) fn lint<'tcx, L>(
 {
     let (span, frames) = get_span_and_frames(tcx, &machine.stack);
 
-    tcx.emit_node_span_lint(
-        lint,
-        // We use the root frame for this so the crate that defines the const defines whether the
-        // lint is emitted.
-        machine.stack.first().and_then(|frame| frame.lint_root()).unwrap_or(CRATE_HIR_ID),
-        span,
-        decorator(frames),
-    );
+    tcx.emit_node_span_lint(lint, machine.best_lint_scope(*tcx), span, decorator(frames));
 }

compiler/rustc_const_eval/src/const_eval/eval_queries.rs

@@ -114,7 +114,7 @@ fn eval_body_using_ecx<'tcx, R: InterpretationResult<'tcx>>(
             let err_diag = errors::MutablePtrInFinal { span: ecx.tcx.span, kind: intern_kind };
             ecx.tcx.emit_node_span_lint(
                 lint::builtin::CONST_EVAL_MUTABLE_PTR_IN_FINAL_VALUE,
-                ecx.best_lint_scope(),
+                ecx.machine.best_lint_scope(*ecx.tcx),
                 err_diag.span,
                 err_diag,
             )

compiler/rustc_const_eval/src/const_eval/machine.rs

@@ -9,12 +9,13 @@ use rustc_data_structures::fx::IndexEntry;
 use rustc_hir::def_id::DefId;
 use rustc_hir::def_id::LocalDefId;
 use rustc_hir::LangItem;
+use rustc_hir::{self as hir, CRATE_HIR_ID};
 use rustc_middle::bug;
 use rustc_middle::mir;
 use rustc_middle::mir::AssertMessage;
 use rustc_middle::query::TyCtxtAt;
-use rustc_middle::ty;
 use rustc_middle::ty::layout::{FnAbiOf, TyAndLayout};
+use rustc_middle::ty::{self, TyCtxt};
 use rustc_session::lint::builtin::WRITES_THROUGH_IMMUTABLE_POINTER;
 use rustc_span::symbol::{sym, Symbol};
 use rustc_span::Span;
@@ -369,6 +370,15 @@ impl<'tcx> CompileTimeInterpCx<'tcx> {
     }
 }
 
+impl<'tcx> CompileTimeMachine<'tcx> {
+    #[inline(always)]
+    /// Find the first stack frame that is within the current crate, if any.
+    /// Otherwise, return the crate's HirId
+    pub fn best_lint_scope(&self, tcx: TyCtxt<'tcx>) -> hir::HirId {
+        self.stack.iter().find_map(|frame| frame.lint_root(tcx)).unwrap_or(CRATE_HIR_ID)
+    }
+}
+
 impl<'tcx> interpret::Machine<'tcx> for CompileTimeMachine<'tcx> {
     compile_time_machine!(<'tcx>);
 
@@ -600,7 +610,7 @@ impl<'tcx> interpret::Machine<'tcx> for CompileTimeMachine<'tcx> {
                 // By default, we stop after a million steps, but the user can disable this lint
                 // to be able to run until the heat death of the universe or power loss, whichever
                 // comes first.
-                let hir_id = ecx.best_lint_scope();
+                let hir_id = ecx.machine.best_lint_scope(*ecx.tcx);
                 let is_error = ecx
                     .tcx
                     .lint_level_at_node(

compiler/rustc_const_eval/src/interpret/eval_context.rs

@@ -4,7 +4,6 @@ use std::{fmt, mem};
 use either::{Either, Left, Right};
 use tracing::{debug, info, info_span, instrument, trace};
 
-use hir::CRATE_HIR_ID;
 use rustc_errors::DiagCtxt;
 use rustc_hir::{self as hir, def_id::DefId, definitions::DefPathData};
 use rustc_index::IndexVec;
@@ -271,13 +270,18 @@ impl<'tcx, Prov: Provenance, Extra> Frame<'tcx, Prov, Extra> {
         }
     }
 
-    pub fn lint_root(&self) -> Option<hir::HirId> {
-        self.current_source_info().and_then(|source_info| {
-            match &self.body.source_scopes[source_info.scope].local_data {
+    pub fn lint_root(&self, tcx: TyCtxt<'tcx>) -> Option<hir::HirId> {
+        // We first try to get a HirId via the current source scope,
+        // and fall back to `body.source`.
+        self.current_source_info()
+            .and_then(|source_info| match &self.body.source_scopes[source_info.scope].local_data {
                 mir::ClearCrossCrate::Set(data) => Some(data.lint_root),
                 mir::ClearCrossCrate::Clear => None,
-            }
-        })
+            })
+            .or_else(|| {
+                let def_id = self.body.source.def_id().as_local();
+                def_id.map(|def_id| tcx.local_def_id_to_hir_id(def_id))
+            })
     }
 
     /// Returns the address of the buffer where the locals are stored. This is used by `Place` as a
@@ -507,15 +511,6 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         self.stack().last().map_or(self.tcx.span, |f| f.current_span())
     }
 
-    #[inline(always)]
-    /// Find the first stack frame that is within the current crate, if any, otherwise return the crate's HirId
-    pub fn best_lint_scope(&self) -> hir::HirId {
-        self.stack()
-            .iter()
-            .find_map(|frame| frame.body.source.def_id().as_local())
-            .map_or(CRATE_HIR_ID, |def_id| self.tcx.local_def_id_to_hir_id(def_id))
-    }
-
     #[inline(always)]
     pub(crate) fn stack(&self) -> &[Frame<'tcx, M::Provenance, M::FrameExtra>] {
         M::stack(self)