From f0f3b3acf8da0b258500c20622efea0ab6600e44 Mon Sep 17 00:00:00 2001
From: Aman Arora <me@aman-arora.com>
Date: Tue, 6 Jul 2021 05:38:15 -0400
Subject: [PATCH] Make type_implements_trait not a query

---
 clippy_utils/src/ty.rs | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/clippy_utils/src/ty.rs b/clippy_utils/src/ty.rs
index 2808fc35e..8857e77d8 100644
--- a/clippy_utils/src/ty.rs
+++ b/clippy_utils/src/ty.rs
@@ -15,6 +15,7 @@ use rustc_span::sym;
 use rustc_span::symbol::{Ident, Symbol};
 use rustc_span::DUMMY_SP;
 use rustc_trait_selection::traits::query::normalize::AtExt;
+use rustc_trait_selection::infer::InferCtxtExt;
 
 use crate::{match_def_path, must_use_attr};
 
@@ -112,6 +113,7 @@ pub fn has_iter_method(cx: &LateContext<'_>, probably_ref_ty: Ty<'_>) -> Option<
 }
 
 /// Checks whether a type implements a trait.
+/// The function returns false in case the type contains an inference variable.
 /// See also `get_trait_def_id`.
 pub fn implements_trait<'tcx>(
     cx: &LateContext<'tcx>,
@@ -119,18 +121,18 @@ pub fn implements_trait<'tcx>(
     trait_id: DefId,
     ty_params: &[GenericArg<'tcx>],
 ) -> bool {
-    // Do not check on infer_types to avoid panic in evaluate_obligation.
-    if ty.has_infer_types() {
-        return false;
-    }
+    // Clippy shouldn't have infer types
+    assert!(!ty.needs_infer());
+
     let ty = cx.tcx.erase_regions(ty);
     if ty.has_escaping_bound_vars() {
         return false;
     }
     let ty_params = cx.tcx.mk_substs(ty_params.iter());
-    cx.tcx
-        .type_implements_trait((trait_id, ty, ty_params, cx.param_env))
+    cx.tcx.infer_ctxt().enter(|infcx|
+        infcx.type_implements_trait(trait_id, ty, ty_params, cx.param_env)
         .must_apply_modulo_regions()
+    )
 }
 
 /// Checks whether this type implements `Drop`.