From 33370fd9829c5bb843b117d11cc7e948f4b824f6 Mon Sep 17 00:00:00 2001
From: kadmin <julianknodt@gmail.com>
Date: Mon, 22 Mar 2021 23:26:07 +0000
Subject: [PATCH] Update to not have extra match

---
 .../src/infer/error_reporting/mod.rs          | 38 ++++----------
 .../ui/const-generics/defaults/mismatch.rs    | 23 ++++++++
 .../const-generics/defaults/mismatch.stderr   | 52 +++++++++++++++++++
 3 files changed, 85 insertions(+), 28 deletions(-)
 create mode 100644 src/test/ui/const-generics/defaults/mismatch.rs
 create mode 100644 src/test/ui/const-generics/defaults/mismatch.stderr

diff --git a/compiler/rustc_infer/src/infer/error_reporting/mod.rs b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
index 98904206b215c..c171b11e3ffa7 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/mod.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
@@ -67,7 +67,7 @@ use rustc_hir::{Item, ItemKind, Node};
 use rustc_middle::ty::error::TypeError;
 use rustc_middle::ty::{
     self,
-    subst::{Subst, SubstsRef},
+    subst::{GenericArgKind, Subst, SubstsRef},
     Region, Ty, TyCtxt, TypeFoldable,
 };
 use rustc_span::{sym, BytePos, DesugaringKind, Pos, Span};
@@ -958,42 +958,24 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         let generics = self.tcx.generics_of(def_id);
         let mut num_supplied_defaults = 0;
 
-        #[derive(PartialEq, Eq, Copy, Clone)]
-        enum Kind {
-            Const,
-            Type,
-        }
         let default_params = generics.params.iter().rev().filter_map(|param| match param.kind {
-            ty::GenericParamDefKind::Type { has_default: true, .. } => {
-                Some((param.def_id, Kind::Type))
-            }
-            ty::GenericParamDefKind::Const { has_default: true } => {
-                Some((param.def_id, Kind::Const))
-            }
+            ty::GenericParamDefKind::Type { has_default: true, .. } => Some(param.def_id),
+            ty::GenericParamDefKind::Const { has_default: true } => Some(param.def_id),
             _ => None,
         });
-        let mut types = substs.types().rev();
-        let mut consts = substs.consts().rev();
-        for (def_id, kind) in default_params {
-            match kind {
-                Kind::Const => {
-                    if let Some(actual) = consts.next() {
-                        if ty::Const::from_anon_const(self.tcx, def_id.expect_local()) != actual {
-                            break;
-                        }
-                    } else {
+        for (def_id, actual) in default_params.zip(substs.iter().rev()) {
+            match actual.unpack() {
+                GenericArgKind::Const(c) => {
+                    if self.tcx.const_param_default(def_id).subst(self.tcx, substs) != c {
                         break;
                     }
                 }
-                Kind::Type => {
-                    if let Some(actual) = types.next() {
-                        if self.tcx.type_of(def_id).subst(self.tcx, substs) != actual {
-                            break;
-                        }
-                    } else {
+                GenericArgKind::Type(ty) => {
+                    if self.tcx.type_of(def_id).subst(self.tcx, substs) != ty {
                         break;
                     }
                 }
+                _ => break,
             }
             num_supplied_defaults += 1;
         }
diff --git a/src/test/ui/const-generics/defaults/mismatch.rs b/src/test/ui/const-generics/defaults/mismatch.rs
new file mode 100644
index 0000000000000..bf578468bb617
--- /dev/null
+++ b/src/test/ui/const-generics/defaults/mismatch.rs
@@ -0,0 +1,23 @@
+#![feature(const_generics)]
+#![feature(const_generics_defaults)]
+#![allow(incomplete_features)]
+
+pub struct Example<const N: usize=13>;
+pub struct Example2<T=u32, const N: usize=13>(T);
+pub struct Example3<const N: usize=13, T=u32>(T);
+pub struct Example4<const N: usize=13, const M: usize=4>;
+
+fn main() {
+  let e: Example::<13> = ();
+  //~^ Error: mismatched types
+  let e: Example2::<u32, 13> = ();
+  //~^ Error: mismatched types
+  let e: Example3::<13, u32> = ();
+  //~^ Error: mismatched types
+  let e: Example3::<7> = ();
+  //~^ Error: mismatched types
+  // FIXME(const_generics_defaults): There should be a note for the error below, but it is
+  // missing.
+  let e: Example4::<7> = ();
+  //~^ Error: mismatched types
+}
diff --git a/src/test/ui/const-generics/defaults/mismatch.stderr b/src/test/ui/const-generics/defaults/mismatch.stderr
new file mode 100644
index 0000000000000..c66eb4cd64594
--- /dev/null
+++ b/src/test/ui/const-generics/defaults/mismatch.stderr
@@ -0,0 +1,52 @@
+error[E0308]: mismatched types
+  --> $DIR/mismatch.rs:11:26
+   |
+LL |   let e: Example::<13> = ();
+   |          -------------   ^^ expected struct `Example`, found `()`
+   |          |
+   |          expected due to this
+
+error[E0308]: mismatched types
+  --> $DIR/mismatch.rs:13:32
+   |
+LL |   let e: Example2::<u32, 13> = ();
+   |          -------------------   ^^ expected struct `Example2`, found `()`
+   |          |
+   |          expected due to this
+   |
+   = note: expected struct `Example2`
+           found unit type `()`
+
+error[E0308]: mismatched types
+  --> $DIR/mismatch.rs:15:32
+   |
+LL |   let e: Example3::<13, u32> = ();
+   |          -------------------   ^^ expected struct `Example3`, found `()`
+   |          |
+   |          expected due to this
+   |
+   = note: expected struct `Example3`
+           found unit type `()`
+
+error[E0308]: mismatched types
+  --> $DIR/mismatch.rs:17:26
+   |
+LL |   let e: Example3::<7> = ();
+   |          -------------   ^^ expected struct `Example3`, found `()`
+   |          |
+   |          expected due to this
+   |
+   = note: expected struct `Example3<7_usize>`
+           found unit type `()`
+
+error[E0308]: mismatched types
+  --> $DIR/mismatch.rs:21:26
+   |
+LL |   let e: Example4::<7> = ();
+   |          -------------   ^^ expected struct `Example4`, found `()`
+   |          |
+   |          expected due to this
+
+error: aborting due to 5 previous errors
+
+For more information about this error, try `rustc --explain E0308`.