Expose try_destructure_mir_constant_for_diagnostics directly to clippy

Otherwise clippy tries to use the query in ways that incremental caching will inevitably cause problems with.

Author: oli-obk

compiler/rustc_const_eval/src/const_eval/mod.rs

@@ -85,7 +85,7 @@ pub(crate) fn eval_to_valtree<'tcx>(
 }
 
 #[instrument(skip(tcx), level = "debug")]
-pub(crate) fn try_destructure_mir_constant_for_diagnostics<'tcx>(
+pub fn try_destructure_mir_constant_for_diagnostics<'tcx>(
     tcx: TyCtxt<'tcx>,
     val: ConstValue<'tcx>,
     ty: Ty<'tcx>,

src/tools/clippy/clippy_utils/src/consts.rs

@@ -724,7 +724,7 @@ fn field_of_struct<'tcx>(
     field: &Ident,
 ) -> Option<mir::ConstantKind<'tcx>> {
     if let mir::ConstantKind::Val(result, ty) = result
-        && let Some(dc) = lcx.tcx.try_destructure_mir_constant_for_diagnostics((result, ty))
+        && let Some(dc) = rustc_const_eval::const_eval::try_destructure_mir_constant_for_diagnostics(lcx.tcx, result, ty)
         && let Some(dc_variant) = dc.variant
         && let Some(variant) = adt_def.variants().get(dc_variant)
         && let Some(field_idx) = variant.fields.iter().position(|el| el.name == field.name)