use precise spans for recursive const evaluation

Author: RalfJung

compiler/rustc_const_eval/src/interpret/eval_context.rs

@@ -926,7 +926,8 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             self.param_env
         };
         let param_env = param_env.with_const();
-        let val = self.tcx.eval_to_allocation_raw(param_env.and(gid))?;
+        // Use a precise span for better cycle errors.
+        let val = self.tcx.at(self.cur_span()).eval_to_allocation_raw(param_env.and(gid))?;
         self.raw_const_to_mplace(val)
     }
 

compiler/rustc_const_eval/src/interpret/memory.rs

@@ -504,7 +504,8 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                     throw_unsup!(ReadExternStatic(def_id));
                 }
 
-                (self.tcx.eval_static_initializer(def_id)?, Some(def_id))
+                // Use a precise span for better cycle errors.
+                (self.tcx.at(self.cur_span()).eval_static_initializer(def_id)?, Some(def_id))
             }
         };
         M::before_access_global(*self.tcx, &self.machine, id, alloc, def_id, is_write)?;

compiler/rustc_const_eval/src/interpret/step.rs

@@ -55,7 +55,6 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         };
         let basic_block = &self.body().basic_blocks()[loc.block];
 
-
         if let Some(stmt) = basic_block.statements.get(loc.statement_index) {
             let old_frames = self.frame_idx();
             self.statement(stmt)?;

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

@@ -3,9 +3,9 @@ use super::{ErrorHandled, EvalToConstValueResult, GlobalId};
 use crate::mir;
 use crate::ty::fold::TypeFoldable;
 use crate::ty::subst::InternalSubsts;
-use crate::ty::{self, TyCtxt};
+use crate::ty::{self, query::TyCtxtAt, TyCtxt};
 use rustc_hir::def_id::DefId;
-use rustc_span::Span;
+use rustc_span::{Span, DUMMY_SP};
 
 impl<'tcx> TyCtxt<'tcx> {
     /// Evaluates a constant without providing any substitutions. This is useful to evaluate consts
@@ -86,14 +86,25 @@ impl<'tcx> TyCtxt<'tcx> {
         }
     }
 
+    /// Evaluate a static's initializer, returning the allocation of the initializer's memory.
+    #[inline(always)]
+    pub fn eval_static_initializer(
+        self,
+        def_id: DefId,
+    ) -> Result<mir::ConstAllocation<'tcx>, ErrorHandled> {
+        self.at(DUMMY_SP).eval_static_initializer(def_id)
+    }
+}
+
+impl<'tcx> TyCtxtAt<'tcx> {
     /// Evaluate a static's initializer, returning the allocation of the initializer's memory.
     pub fn eval_static_initializer(
         self,
         def_id: DefId,
     ) -> Result<mir::ConstAllocation<'tcx>, ErrorHandled> {
         trace!("eval_static_initializer: Need to compute {:?}", def_id);
         assert!(self.is_static(def_id));
-        let instance = ty::Instance::mono(self, def_id);
+        let instance = ty::Instance::mono(*self, def_id);
         let gid = GlobalId { instance, promoted: None };
         self.eval_to_allocation(gid, ty::ParamEnv::reveal_all())
     }
@@ -109,7 +120,9 @@ impl<'tcx> TyCtxt<'tcx> {
         let raw_const = self.eval_to_allocation_raw(param_env.and(gid))?;
         Ok(self.global_alloc(raw_const.alloc_id).unwrap_memory())
     }
+}
 
+impl<'tcx> TyCtxt<'tcx> {
     /// Destructure a type-level constant ADT or array into its variant index and its field values.
     /// Panics if the destructuring fails, use `try_destructure_const` for fallible version.
     pub fn destructure_const(

src/test/ui/consts/recursive-zst-static.default.stderr

@@ -5,10 +5,10 @@ LL | static FOO: () = FOO;
    | ^^^^^^^^^^^^^^^^^^^^^
    |
 note: ...which requires const-evaluating + checking `FOO`...
-  --> $DIR/recursive-zst-static.rs:10:1
+  --> $DIR/recursive-zst-static.rs:10:18
    |
 LL | static FOO: () = FOO;
-   | ^^^^^^^^^^^^^^^^^^^^^
+   |                  ^^^
    = note: ...which again requires const-evaluating + checking `FOO`, completing the cycle
    = note: cycle used when running analysis passes on this crate
 

src/test/ui/consts/recursive-zst-static.unleash.stderr

@@ -5,10 +5,10 @@ LL | static FOO: () = FOO;
    | ^^^^^^^^^^^^^^^^^^^^^
    |
 note: ...which requires const-evaluating + checking `FOO`...
-  --> $DIR/recursive-zst-static.rs:10:1
+  --> $DIR/recursive-zst-static.rs:10:18
    |
 LL | static FOO: () = FOO;
-   | ^^^^^^^^^^^^^^^^^^^^^
+   |                  ^^^
    = note: ...which again requires const-evaluating + checking `FOO`, completing the cycle
    = note: cycle used when running analysis passes on this crate
 

src/test/ui/consts/write-to-static-mut-in-static.stderr

@@ -11,10 +11,10 @@ LL | pub static mut C: u32 = unsafe { C = 1; 0 };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
 note: ...which requires const-evaluating + checking `C`...
-  --> $DIR/write-to-static-mut-in-static.rs:5:1
+  --> $DIR/write-to-static-mut-in-static.rs:5:34
    |
 LL | pub static mut C: u32 = unsafe { C = 1; 0 };
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                  ^^^^^
    = note: ...which again requires const-evaluating + checking `C`, completing the cycle
    = note: cycle used when running analysis passes on this crate
 

src/test/ui/recursion/recursive-static-definition.stderr

@@ -5,10 +5,10 @@ LL | pub static FOO: u32 = FOO;
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
 note: ...which requires const-evaluating + checking `FOO`...
-  --> $DIR/recursive-static-definition.rs:1:1
+  --> $DIR/recursive-static-definition.rs:1:23
    |
 LL | pub static FOO: u32 = FOO;
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                       ^^^
    = note: ...which again requires const-evaluating + checking `FOO`, completing the cycle
    = note: cycle used when running analysis passes on this crate