Improve `LocalDecl` creation.

This commit adds some new `LocalDecl` methods:
- `with_source_info`, a most general constructor.
- `new`, a variant of `with_source_info` which represents the most
  common use case.
- `internal` a modifying method (like the already present `immutable`).

It removes some old `LocalDecl` methods:
- `new_internal` and `new_local`, because they're subsumed by the new
  methods.
- `new_return_place`, because it was identical to `new_temp`.

Finally, it cleans up all the use sites.

13 files changed, 70 insertions, 137 deletions

diff --git a/src/librustc_middle/mir/mod.rs b/src/librustc_middle/mir/mod.rs
index e5f70d7ef99..adcbaba5a69 100644
--- a/src/librustc_middle/mir/mod.rs
+++ b/src/librustc_middle/mir/mod.rs
@@ -918,10 +918,31 @@ impl<'tcx> LocalDecl<'tcx> {
         self.source_info.span.desugaring_kind().is_some()
     }
 
-    /// Creates a new `LocalDecl` for a temporary.
+    /// Creates a new `LocalDecl` for a temporary: mutable, non-internal.
     #[inline]
-    pub fn new_temp(ty: Ty<'tcx>, span: Span) -> Self {
-        Self::new_local(ty, Mutability::Mut, false, span)
+    pub fn new(ty: Ty<'tcx>, span: Span) -> Self {
+        Self::with_source_info(ty, SourceInfo::outermost(span))
+    }
+
+    /// Like `LocalDecl::new`, but takes a `SourceInfo` instead of a `Span`.
+    #[inline]
+    pub fn with_source_info(ty: Ty<'tcx>, source_info: SourceInfo) -> Self {
+        LocalDecl {
+            mutability: Mutability::Mut,
+            local_info: LocalInfo::Other,
+            internal: false,
+            is_block_tail: None,
+            ty,
+            user_ty: UserTypeProjections::none(),
+            source_info,
+        }
+    }
+
+    /// Converts `self` into same `LocalDecl` except tagged as internal.
+    #[inline]
+    pub fn internal(mut self) -> Self {
+        self.internal = true;
+        self
     }
 
     /// Converts `self` into same `LocalDecl` except tagged as immutable.
@@ -938,41 +959,6 @@ impl<'tcx> LocalDecl<'tcx> {
         self.is_block_tail = Some(info);
         self
     }
-
-    /// Creates a new `LocalDecl` for a internal temporary.
-    #[inline]
-    pub fn new_internal(ty: Ty<'tcx>, span: Span) -> Self {
-        Self::new_local(ty, Mutability::Mut, true, span)
-    }
-
-    #[inline]
-    fn new_local(ty: Ty<'tcx>, mutability: Mutability, internal: bool, span: Span) -> Self {
-        LocalDecl {
-            mutability,
-            ty,
-            user_ty: UserTypeProjections::none(),
-            source_info: SourceInfo::outermost(span),
-            internal,
-            local_info: LocalInfo::Other,
-            is_block_tail: None,
-        }
-    }
-
-    /// Builds a `LocalDecl` for the return place.
-    ///
-    /// This must be inserted into the `local_decls` list as the first local.
-    #[inline]
-    pub fn new_return_place(return_ty: Ty<'_>, span: Span) -> LocalDecl<'_> {
-        LocalDecl {
-            mutability: Mutability::Mut,
-            ty: return_ty,
-            user_ty: UserTypeProjections::none(),
-            source_info: SourceInfo::outermost(span),
-            internal: false,
-            is_block_tail: None,
-            local_info: LocalInfo::Other,
-        }
-    }
 }
 
 /// Debug information pertaining to a user variable.
diff --git a/src/librustc_mir/shim.rs b/src/librustc_mir/shim.rs
index a58ac7cfe18..847f59b95e9 100644
--- a/src/librustc_mir/shim.rs
+++ b/src/librustc_mir/shim.rs
@@ -145,24 +145,12 @@ enum CallKind {
     Direct(DefId),
 }
 
-fn temp_decl(mutability: Mutability, ty: Ty<'_>, span: Span) -> LocalDecl<'_> {
-    LocalDecl {
-        mutability,
-        ty,
-        user_ty: UserTypeProjections::none(),
-        source_info: SourceInfo::outermost(span),
-        internal: false,
-        local_info: LocalInfo::Other,
-        is_block_tail: None,
-    }
-}
-
 fn local_decls_for_sig<'tcx>(
     sig: &ty::FnSig<'tcx>,
     span: Span,
 ) -> IndexVec<Local, LocalDecl<'tcx>> {
-    iter::once(temp_decl(Mutability::Mut, sig.output(), span))
-        .chain(sig.inputs().iter().map(|ity| temp_decl(Mutability::Not, ity, span)))
+    iter::once(LocalDecl::new(sig.output(), span))
+        .chain(sig.inputs().iter().map(|ity| LocalDecl::new(ity, span).immutable()))
         .collect()
 }
 
@@ -413,7 +401,11 @@ impl CloneShimBuilder<'tcx> {
 
     fn make_place(&mut self, mutability: Mutability, ty: Ty<'tcx>) -> Place<'tcx> {
         let span = self.span;
-        Place::from(self.local_decls.push(temp_decl(mutability, ty, span)))
+        let mut local = LocalDecl::new(ty, span);
+        if mutability == Mutability::Not {
+            local = local.immutable();
+        }
+        Place::from(self.local_decls.push(local))
     }
 
     fn make_clone_call(
@@ -497,7 +489,7 @@ impl CloneShimBuilder<'tcx> {
         let tcx = self.tcx;
         let span = self.span;
 
-        let beg = self.local_decls.push(temp_decl(Mutability::Mut, tcx.types.usize, span));
+        let beg = self.local_decls.push(LocalDecl::new(tcx.types.usize, span));
         let end = self.make_place(Mutability::Not, tcx.types.usize);
 
         // BB #0
@@ -552,7 +544,7 @@ impl CloneShimBuilder<'tcx> {
         // `let mut beg = 0;`
         // goto #6;
         let end = beg;
-        let beg = self.local_decls.push(temp_decl(Mutability::Mut, tcx.types.usize, span));
+        let beg = self.local_decls.push(LocalDecl::new(tcx.types.usize, span));
         let init = self.make_statement(StatementKind::Assign(box (
             Place::from(beg),
             Rvalue::Use(Operand::Constant(self.make_usize(0))),
@@ -700,14 +692,16 @@ fn build_call_shim<'tcx>(
         Adjustment::DerefMove => Operand::Move(tcx.mk_place_deref(rcvr_place())),
         Adjustment::RefMut => {
             // let rcvr = &mut rcvr;
-            let ref_rcvr = local_decls.push(temp_decl(
-                Mutability::Not,
-                tcx.mk_ref(
-                    tcx.lifetimes.re_erased,
-                    ty::TypeAndMut { ty: sig.inputs()[0], mutbl: hir::Mutability::Mut },
-                ),
-                span,
-            ));
+            let ref_rcvr = local_decls.push(
+                LocalDecl::new(
+                    tcx.mk_ref(
+                        tcx.lifetimes.re_erased,
+                        ty::TypeAndMut { ty: sig.inputs()[0], mutbl: hir::Mutability::Mut },
+                    ),
+                    span,
+                )
+                .immutable(),
+            );
             let borrow_kind = BorrowKind::Mut { allow_two_phase_borrow: false };
             statements.push(Statement {
                 source_info,
diff --git a/src/librustc_mir/transform/generator.rs b/src/librustc_mir/transform/generator.rs
index a9d566c92e9..91f0297710e 100644
--- a/src/librustc_mir/transform/generator.rs
+++ b/src/librustc_mir/transform/generator.rs
@@ -255,7 +255,7 @@ impl TransformVisitor<'tcx> {
 
     // Create a statement which reads the discriminant into a temporary
     fn get_discr(&self, body: &mut Body<'tcx>) -> (Statement<'tcx>, Place<'tcx>) {
-        let temp_decl = LocalDecl::new_internal(self.tcx.types.isize, body.span);
+        let temp_decl = LocalDecl::new(self.tcx.types.isize, body.span).internal();
         let local_decls_len = body.local_decls.push(temp_decl);
         let temp = Place::from(local_decls_len);
 
@@ -395,16 +395,7 @@ fn replace_local<'tcx>(
     body: &mut Body<'tcx>,
     tcx: TyCtxt<'tcx>,
 ) -> Local {
-    let source_info = SourceInfo::outermost(body.span);
-    let new_decl = LocalDecl {
-        mutability: Mutability::Mut,
-        ty,
-        user_ty: UserTypeProjections::none(),
-        source_info,
-        internal: false,
-        is_block_tail: None,
-        local_info: LocalInfo::Other,
-    };
+    let new_decl = LocalDecl::new(ty, body.span);
     let new_local = body.local_decls.push(new_decl);
     body.local_decls.swap(local, new_local);
 
@@ -877,28 +868,15 @@ fn create_generator_drop_shim<'tcx>(
     }
 
     // Replace the return variable
-    body.local_decls[RETURN_PLACE] = LocalDecl {
-        mutability: Mutability::Mut,
-        ty: tcx.mk_unit(),
-        user_ty: UserTypeProjections::none(),
-        source_info,
-        internal: false,
-        is_block_tail: None,
-        local_info: LocalInfo::Other,
-    };
+    body.local_decls[RETURN_PLACE] = LocalDecl::with_source_info(tcx.mk_unit(), source_info);
 
     make_generator_state_argument_indirect(tcx, &mut body);
 
     // Change the generator argument from &mut to *mut
-    body.local_decls[SELF_ARG] = LocalDecl {
-        mutability: Mutability::Mut,
-        ty: tcx.mk_ptr(ty::TypeAndMut { ty: gen_ty, mutbl: hir::Mutability::Mut }),
-        user_ty: UserTypeProjections::none(),
+    body.local_decls[SELF_ARG] = LocalDecl::with_source_info(
+        tcx.mk_ptr(ty::TypeAndMut { ty: gen_ty, mutbl: hir::Mutability::Mut }),
         source_info,
-        internal: false,
-        is_block_tail: None,
-        local_info: LocalInfo::Other,
-    };
+    );
     if tcx.sess.opts.debugging_opts.mir_emit_retag {
         // Alias tracking must know we changed the type
         body.basic_blocks_mut()[START_BLOCK].statements.insert(
diff --git a/src/librustc_mir/transform/inline.rs b/src/librustc_mir/transform/inline.rs
index 985bd2b1660..a8e949ecb31 100644
--- a/src/librustc_mir/transform/inline.rs
+++ b/src/librustc_mir/transform/inline.rs
@@ -480,7 +480,7 @@ impl Inliner<'tcx> {
 
                     let ty = dest.ty(caller_body, self.tcx);
 
-                    let temp = LocalDecl::new_temp(ty, callsite.location.span);
+                    let temp = LocalDecl::new(ty, callsite.location.span);
 
                     let tmp = caller_body.local_decls.push(temp);
                     let tmp = Place::from(tmp);
@@ -631,7 +631,7 @@ impl Inliner<'tcx> {
 
         let ty = arg.ty(caller_body, self.tcx);
 
-        let arg_tmp = LocalDecl::new_temp(ty, callsite.location.span);
+        let arg_tmp = LocalDecl::new(ty, callsite.location.span);
         let arg_tmp = caller_body.local_decls.push(arg_tmp);
 
         let stmt = Statement {
diff --git a/src/librustc_mir/transform/promote_consts.rs b/src/librustc_mir/transform/promote_consts.rs
index 8559e0a20ea..ebb162eca46 100644
--- a/src/librustc_mir/transform/promote_consts.rs
+++ b/src/librustc_mir/transform/promote_consts.rs
@@ -815,7 +815,7 @@ impl<'a, 'tcx> Promoter<'a, 'tcx> {
         }
 
         let num_stmts = self.source[loc.block].statements.len();
-        let new_temp = self.promoted.local_decls.push(LocalDecl::new_temp(
+        let new_temp = self.promoted.local_decls.push(LocalDecl::new(
             self.source.local_decls[temp].ty,
             self.source.local_decls[temp].source_info.span,
         ));
@@ -915,7 +915,7 @@ impl<'a, 'tcx> Promoter<'a, 'tcx> {
             let tcx = self.tcx;
             let mut promoted_operand = |ty, span| {
                 promoted.span = span;
-                promoted.local_decls[RETURN_PLACE] = LocalDecl::new_return_place(ty, span);
+                promoted.local_decls[RETURN_PLACE] = LocalDecl::new(ty, span);
 
                 Operand::Constant(Box::new(Constant {
                     span,
@@ -963,7 +963,7 @@ impl<'a, 'tcx> Promoter<'a, 'tcx> {
                             // Create a temp to hold the promoted reference.
                             // This is because `*r` requires `r` to be a local,
                             // otherwise we would use the `promoted` directly.
-                            let mut promoted_ref = LocalDecl::new_temp(ref_ty, span);
+                            let mut promoted_ref = LocalDecl::new(ref_ty, span);
                             promoted_ref.source_info = statement.source_info;
                             let promoted_ref = local_decls.push(promoted_ref);
                             assert_eq!(self.temps.push(TempState::Unpromotable), promoted_ref);
@@ -1081,8 +1081,7 @@ pub fn promote_candidates<'tcx>(
         }
 
         // Declare return place local so that `mir::Body::new` doesn't complain.
-        let initial_locals =
-            iter::once(LocalDecl::new_return_place(tcx.types.never, body.span)).collect();
+        let initial_locals = iter::once(LocalDecl::new(tcx.types.never, body.span)).collect();
 
         let mut promoted = Body::new(
             IndexVec::new(),
diff --git a/src/librustc_mir/util/patch.rs b/src/librustc_mir/util/patch.rs
index c1c97909b3c..6566a996fe4 100644
--- a/src/librustc_mir/util/patch.rs
+++ b/src/librustc_mir/util/patch.rs
@@ -83,14 +83,14 @@ impl<'tcx> MirPatch<'tcx> {
     pub fn new_temp(&mut self, ty: Ty<'tcx>, span: Span) -> Local {
         let index = self.next_local;
         self.next_local += 1;
-        self.new_locals.push(LocalDecl::new_temp(ty, span));
+        self.new_locals.push(LocalDecl::new(ty, span));
         Local::new(index as usize)
     }
 
     pub fn new_internal(&mut self, ty: Ty<'tcx>, span: Span) -> Local {
         let index = self.next_local;
         self.next_local += 1;
-        self.new_locals.push(LocalDecl::new_internal(ty, span));
+        self.new_locals.push(LocalDecl::new(ty, span).internal());
         Local::new(index as usize)
     }
 
diff --git a/src/librustc_mir_build/build/expr/as_place.rs b/src/librustc_mir_build/build/expr/as_place.rs
index 9f74385b336..e08eedc6b6e 100644
--- a/src/librustc_mir_build/build/expr/as_place.rs
+++ b/src/librustc_mir_build/build/expr/as_place.rs
@@ -383,7 +383,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                         let fake_borrow_ty =
                             tcx.mk_imm_ref(tcx.lifetimes.re_erased, fake_borrow_deref_ty);
                         let fake_borrow_temp =
-                            self.local_decls.push(LocalDecl::new_temp(fake_borrow_ty, expr_span));
+                            self.local_decls.push(LocalDecl::new(fake_borrow_ty, expr_span));
                         let projection = tcx.intern_place_elems(&base_place.projection[..idx]);
                         self.cfg.push_assign(
                             block,
diff --git a/src/librustc_mir_build/build/expr/as_rvalue.rs b/src/librustc_mir_build/build/expr/as_rvalue.rs
index 38f71135c7d..d934ba1dc84 100644
--- a/src/librustc_mir_build/build/expr/as_rvalue.rs
+++ b/src/librustc_mir_build/build/expr/as_rvalue.rs
@@ -97,7 +97,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 // The `Box<T>` temporary created here is not a part of the HIR,
                 // and therefore is not considered during generator OIBIT
                 // determination. See the comment about `box` at `yield_in_scope`.
-                let result = this.local_decls.push(LocalDecl::new_internal(expr.ty, expr_span));
+                let result = this.local_decls.push(LocalDecl::new(expr.ty, expr_span).internal());
                 this.cfg.push(
                     block,
                     Statement { source_info, kind: StatementKind::StorageLive(result) },
@@ -377,7 +377,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         let this = self;
 
         let source_info = this.source_info(upvar_span);
-        let temp = this.local_decls.push(LocalDecl::new_temp(upvar_ty, upvar_span));
+        let temp = this.local_decls.push(LocalDecl::new(upvar_ty, upvar_span));
 
         this.cfg.push(block, Statement { source_info, kind: StatementKind::StorageLive(temp) });
 
diff --git a/src/librustc_mir_build/build/expr/as_temp.rs b/src/librustc_mir_build/build/expr/as_temp.rs
index b4ef536afb7..16ca2057584 100644
--- a/src/librustc_mir_build/build/expr/as_temp.rs
+++ b/src/librustc_mir_build/build/expr/as_temp.rs
@@ -47,7 +47,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
 
         let expr_ty = expr.ty;
         let temp = {
-            let mut local_decl = LocalDecl::new_temp(expr_ty, expr_span);
+            let mut local_decl = LocalDecl::new(expr_ty, expr_span);
             if mutability == Mutability::Not {
                 local_decl = local_decl.immutable();
             }
diff --git a/src/librustc_mir_build/build/expr/into.rs b/src/librustc_mir_build/build/expr/into.rs
index 52336b40a48..e26fb48a3f9 100644
--- a/src/librustc_mir_build/build/expr/into.rs
+++ b/src/librustc_mir_build/build/expr/into.rs
@@ -187,15 +187,10 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     let ptr_ty = ptr.ty;
                     // Create an *internal* temp for the pointer, so that unsafety
                     // checking won't complain about the raw pointer assignment.
-                    let ptr_temp = this.local_decls.push(LocalDecl {
-                        mutability: Mutability::Mut,
-                        ty: ptr_ty,
-                        user_ty: UserTypeProjections::none(),
+                    let ptr_temp = this.local_decls.push(LocalDecl::with_source_info(
+                        ptr_ty,
                         source_info,
-                        internal: true,
-                        local_info: LocalInfo::Other,
-                        is_block_tail: None,
-                    });
+                    ).internal());
                     let ptr_temp = Place::from(ptr_temp);
                     let block = unpack!(this.into(ptr_temp, block, ptr));
                     this.into(this.hir.tcx().mk_place_deref(ptr_temp), block, val)
@@ -348,7 +343,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 // value is Sized. Usually, this is caught in type checking, but
                 // in the case of box expr there is no such check.
                 if !destination.projection.is_empty() {
-                    this.local_decls.push(LocalDecl::new_temp(expr.ty, expr.span));
+                    this.local_decls.push(LocalDecl::new(expr.ty, expr.span));
                 }
 
                 debug_assert!(Category::of(&expr.kind) == Some(Category::Place));
diff --git a/src/librustc_mir_build/build/matches/mod.rs b/src/librustc_mir_build/build/matches/mod.rs
index b9d61458a83..03fdd2ed8f1 100644
--- a/src/librustc_mir_build/build/matches/mod.rs
+++ b/src/librustc_mir_build/build/matches/mod.rs
@@ -1539,7 +1539,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 let fake_borrow_deref_ty = matched_place.ty(&self.local_decls, tcx).ty;
                 let fake_borrow_ty = tcx.mk_imm_ref(tcx.lifetimes.re_erased, fake_borrow_deref_ty);
                 let fake_borrow_temp =
-                    self.local_decls.push(LocalDecl::new_temp(fake_borrow_ty, temp_span));
+                    self.local_decls.push(LocalDecl::new(fake_borrow_ty, temp_span));
 
                 (matched_place, fake_borrow_temp)
             })
diff --git a/src/librustc_mir_build/build/misc.rs b/src/librustc_mir_build/build/misc.rs
index 578b862b905..e8933ff8aa7 100644
--- a/src/librustc_mir_build/build/misc.rs
+++ b/src/librustc_mir_build/build/misc.rs
@@ -15,7 +15,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
     /// N.B., **No cleanup is scheduled for this temporary.** You should
     /// call `schedule_drop` once the temporary is initialized.
     crate fn temp(&mut self, ty: Ty<'tcx>, span: Span) -> Place<'tcx> {
-        let temp = self.local_decls.push(LocalDecl::new_temp(ty, span));
+        let temp = self.local_decls.push(LocalDecl::new(ty, span));
         let place = Place::from(temp);
         debug!("temp: created temp {:?} with type {:?}", place, self.local_decls[temp].ty);
         place
diff --git a/src/librustc_mir_build/build/mod.rs b/src/librustc_mir_build/build/mod.rs
index 9a02b92145c..a668cb86910 100644
--- a/src/librustc_mir_build/build/mod.rs
+++ b/src/librustc_mir_build/build/mod.rs
@@ -708,15 +708,7 @@ fn construct_error<'a, 'tcx>(hir: Cx<'a, 'tcx>, body_id: hir::BodyId) -> Body<'t
     // Some MIR passes will expect the number of parameters to match the
     // function declaration.
     for _ in 0..num_params {
-        builder.local_decls.push(LocalDecl {
-            mutability: Mutability::Mut,
-            ty,
-            user_ty: UserTypeProjections::none(),
-            source_info,
-            internal: false,
-            local_info: LocalInfo::Other,
-            is_block_tail: None,
-        });
+        builder.local_decls.push(LocalDecl::with_source_info(ty, source_info));
     }
     builder.cfg.terminate(START_BLOCK, source_info, TerminatorKind::Unreachable);
     let mut body = builder.finish();
@@ -750,10 +742,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             guard_context: vec![],
             push_unsafe_count: 0,
             unpushed_unsafe: safety,
-            local_decls: IndexVec::from_elem_n(
-                LocalDecl::new_return_place(return_ty, return_span),
-                1,
-            ),
+            local_decls: IndexVec::from_elem_n(LocalDecl::new(return_ty, return_span), 1),
             canonical_user_type_annotations: IndexVec::new(),
             upvar_mutbls: vec![],
             var_indices: Default::default(),
@@ -806,15 +795,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         for &ArgInfo(ty, _, arg_opt, _) in arguments.iter() {
             let source_info =
                 SourceInfo::outermost(arg_opt.map_or(self.fn_span, |arg| arg.pat.span));
-            let arg_local = self.local_decls.push(LocalDecl {
-                mutability: Mutability::Mut,
-                ty,
-                user_ty: UserTypeProjections::none(),
-                source_info,
-                internal: false,
-                local_info: LocalInfo::Other,
-                is_block_tail: None,
-            });
+            let arg_local = self.local_decls.push(LocalDecl::with_source_info(ty, source_info));
 
             // If this is a simple binding pattern, give debuginfo a nice name.
             if let Some(arg) = arg_opt {