From 65deeae76dfcb8d0aeb389bbe12ef9990caf2f6f Mon Sep 17 00:00:00 2001
From: Mazdak Farrokhzad <twingoow@gmail.com>
Date: Sat, 24 Aug 2019 13:47:07 +0200
Subject: [PATCH] typeck/pat.rs: `check_pat_top` is the entry point.

This clarifies the fact that type checking patterns unconditionally
starts with `BindByValue` as the default binding mode making the
notion of a default binding mode internal to type checking patterns.
---
 src/librustc_typeck/check/_match.rs |  5 ++---
 src/librustc_typeck/check/mod.rs    | 10 ++--------
 src/librustc_typeck/check/pat.rs    | 12 +++++++++++-
 3 files changed, 15 insertions(+), 12 deletions(-)

diff --git a/src/librustc_typeck/check/_match.rs b/src/librustc_typeck/check/_match.rs
index 8cb365d91fa..efc37cc04b2 100644
--- a/src/librustc_typeck/check/_match.rs
+++ b/src/librustc_typeck/check/_match.rs
@@ -3,7 +3,7 @@
 use rustc::hir::{self, ExprKind};
 use rustc::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
 use rustc::traits::{ObligationCause, ObligationCauseCode};
-use rustc::ty::{self, Ty};
+use rustc::ty::Ty;
 use syntax_pos::Span;
 
 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
@@ -59,8 +59,7 @@ pub fn check_match(
             let mut all_pats_diverge = Diverges::WarnedAlways;
             for p in &arm.pats {
                 self.diverges.set(Diverges::Maybe);
-                let binding_mode = ty::BindingMode::BindByValue(hir::Mutability::MutImmutable);
-                self.check_pat_walk(&p, discrim_ty, binding_mode, Some(discrim.span));
+                self.check_pat_top(&p, discrim_ty, Some(discrim.span));
                 all_pats_diverge &= self.diverges.get();
             }
 
diff --git a/src/librustc_typeck/check/mod.rs b/src/librustc_typeck/check/mod.rs
index a130d11a5e6..ee505b24875 100644
--- a/src/librustc_typeck/check/mod.rs
+++ b/src/librustc_typeck/check/mod.rs
@@ -1104,8 +1104,7 @@ fn check_fn<'a, 'tcx>(
     // Add formal parameters.
     for (arg_ty, arg) in fn_sig.inputs().iter().zip(&body.arguments) {
         // Check the pattern.
-        let binding_mode = ty::BindingMode::BindByValue(hir::Mutability::MutImmutable);
-        fcx.check_pat_walk(&arg.pat, arg_ty, binding_mode, None);
+        fcx.check_pat_top(&arg.pat, arg_ty, None);
 
         // Check that argument is Sized.
         // The check for a non-trivial pattern is a hack to avoid duplicate warnings
@@ -3631,12 +3630,7 @@ pub fn check_decl_local(&self, local: &'tcx hir::Local) {
             }
         }
 
-        self.check_pat_walk(
-            &local.pat,
-            t,
-            ty::BindingMode::BindByValue(hir::Mutability::MutImmutable),
-            None,
-        );
+        self.check_pat_top(&local.pat, t, None);
         let pat_ty = self.node_ty(local.pat.hir_id);
         if pat_ty.references_error() {
             self.write_ty(local.hir_id, pat_ty);
diff --git a/src/librustc_typeck/check/pat.rs b/src/librustc_typeck/check/pat.rs
index 59244ec33ca..fc52684b5a2 100644
--- a/src/librustc_typeck/check/pat.rs
+++ b/src/librustc_typeck/check/pat.rs
@@ -29,6 +29,16 @@
 https://doc.rust-lang.org/reference/types.html#trait-objects";
 
 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
+    pub fn check_pat_top(
+        &self,
+        pat: &'tcx hir::Pat,
+        expected: Ty<'tcx>,
+        discrim_span: Option<Span>,
+    ) {
+        let def_bm = ty::BindingMode::BindByValue(hir::Mutability::MutImmutable);
+        self.check_pat_walk(pat, expected, def_bm, discrim_span);
+    }
+
     /// `discrim_span` argument having a `Span` indicates that this pattern is part of a match
     /// expression arm guard, and it points to the match discriminant to add context in type errors.
     /// In the following example, `discrim_span` corresponds to the `a + b` expression:
@@ -45,7 +55,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     ///   = note: expected type `usize`
     ///              found type `std::result::Result<_, _>`
     /// ```
-    pub fn check_pat_walk(
+    fn check_pat_walk(
         &self,
         pat: &'tcx hir::Pat,
         expected: Ty<'tcx>,