Close up a loophole

Author: saethlin

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -1791,10 +1791,13 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                     record!(self.tables.mir_coroutine_witnesses[def_id.to_def_id()] <- witnesses);
                 }
             }
+            let mut is_trivial = false;
             if encode_const {
                 if let Some((val, ty)) = tcx.is_trivial_const(def_id) {
+                    is_trivial = true;
                     record!(self.tables.is_trivial_const[def_id.to_def_id()] <- (val, ty));
                 } else {
+                    is_trivial = false;
                     record!(self.tables.mir_for_ctfe[def_id.to_def_id()] <- tcx.mir_for_ctfe(def_id));
                 }
 
@@ -1814,7 +1817,9 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                     }
                 }
             }
-            record!(self.tables.promoted_mir[def_id.to_def_id()] <- tcx.promoted_mir(def_id));
+            if !is_trivial {
+                record!(self.tables.promoted_mir[def_id.to_def_id()] <- tcx.promoted_mir(def_id));
+            }
 
             if self.tcx.is_coroutine(def_id.to_def_id())
                 && let Some(witnesses) = tcx.mir_coroutine_witnesses(def_id)

compiler/rustc_mir_transform/src/lib.rs

@@ -452,6 +452,10 @@ fn mir_promoted(
     tcx: TyCtxt<'_>,
     def: LocalDefId,
 ) -> (&Steal<Body<'_>>, &Steal<IndexVec<Promoted, Body<'_>>>) {
+    if tcx.is_trivial_const(def).is_some() {
+        panic!("Tried to get MIR of a trivial const");
+    }
+
     // Ensure that we compute the `mir_const_qualif` for constants at
     // this point, before we steal the mir-const result.
     // Also this means promotion can rely on all const checks having been done.
@@ -479,7 +483,9 @@ fn mir_promoted(
         tcx.ensure_done().coroutine_by_move_body_def_id(def);
     }
 
+    // the `is_trivial_const` uses mir_built, so make sure it is run.
     tcx.ensure_done().is_trivial_const(def);
+
     let mut body = tcx.mir_built(def).steal();
     if let Some(error_reported) = const_qualifs.tainted_by_errors {
         body.tainted_by_errors = Some(error_reported);
@@ -542,9 +548,6 @@ fn inner_mir_for_ctfe(tcx: TyCtxt<'_>, def: LocalDefId) -> Body<'_> {
 /// mir borrowck *before* doing so in order to ensure that borrowck can be run and doesn't
 /// end up missing the source MIR due to stealing happening.
 fn mir_drops_elaborated_and_const_checked(tcx: TyCtxt<'_>, def: LocalDefId) -> &Steal<Body<'_>> {
-    if tcx.is_trivial_const(def).is_some() {
-        panic!("Tried to get mir_for_ctfe of a trivial const");
-    }
     if tcx.is_coroutine(def.to_def_id()) {
         tcx.ensure_done().mir_coroutine_witnesses(def);
     }