Auto merge of #62075 - Centril:guardless-match-arms, r=petrochenkov

Remove `ast::Guard`

With the introduction of `ast::ExprKind::Let` in https://github.com/rust-lang/rust/pull/60861, the `ast::Guard` structure is now redundant in terms of representing [`if let` guards](https://github.com/rust-lang/rust/issues/51114) in AST since it can be represented by `ExprKind::Let` syntactically. Therefore, we remove `ast::Guard` here.

However, we keep `hir::Guard` because the semantic representation is a different matter and this story is more unclear right now (might involve `goto 'arm` in HIR or something...).

r? @petrochenkov

5 files changed, 10 insertions, 31 deletions

diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index 21704206cbf..f2fac16db01 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -893,17 +893,12 @@ pub struct Local {
 pub struct Arm {
     pub attrs: Vec<Attribute>,
     pub pats: Vec<P<Pat>>,
-    pub guard: Option<Guard>,
+    pub guard: Option<P<Expr>>,
     pub body: P<Expr>,
     pub span: Span,
 }
 
 #[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
-pub enum Guard {
-    If(P<Expr>),
-}
-
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
 pub struct Field {
     pub ident: Ident,
     pub expr: P<Expr>,
diff --git a/src/libsyntax/mut_visit.rs b/src/libsyntax/mut_visit.rs
index 35aa2eead0b..e23bc025f6e 100644
--- a/src/libsyntax/mut_visit.rs
+++ b/src/libsyntax/mut_visit.rs
@@ -131,10 +131,6 @@ pub trait MutVisitor: Sized {
         noop_visit_arm(a, self);
     }
 
-    fn visit_guard(&mut self, g: &mut Guard) {
-        noop_visit_guard(g, self);
-    }
-
     fn visit_pat(&mut self, p: &mut P<Pat>) {
         noop_visit_pat(p, self);
     }
@@ -389,17 +385,11 @@ pub fn noop_visit_arm<T: MutVisitor>(
 ) {
     visit_attrs(attrs, vis);
     visit_vec(pats, |pat| vis.visit_pat(pat));
-    visit_opt(guard, |guard| vis.visit_guard(guard));
+    visit_opt(guard, |guard| vis.visit_expr(guard));
     vis.visit_expr(body);
     vis.visit_span(span);
 }
 
-pub fn noop_visit_guard<T: MutVisitor>(g: &mut Guard, vis: &mut T) {
-    match g {
-        Guard::If(e) => vis.visit_expr(e),
-    }
-}
-
 pub fn noop_visit_ty_constraint<T: MutVisitor>(
     AssocTyConstraint { id, ident, kind, span }: &mut AssocTyConstraint,
     vis: &mut T
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index b2003e2d6bd..f3ace84162e 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -3,7 +3,7 @@
 use crate::ast::{AngleBracketedArgs, ParenthesizedArgs, AttrStyle, BareFnTy};
 use crate::ast::{GenericBound, TraitBoundModifier};
 use crate::ast::Unsafety;
-use crate::ast::{Mod, AnonConst, Arg, Arm, Guard, Attribute, BindingMode, TraitItemKind};
+use crate::ast::{Mod, AnonConst, Arg, Arm, Attribute, BindingMode, TraitItemKind};
 use crate::ast::Block;
 use crate::ast::{BlockCheckMode, CaptureBy, Movability};
 use crate::ast::{Constness, Crate};
@@ -3396,7 +3396,7 @@ impl<'a> Parser<'a> {
         let lo = self.token.span;
         let pats = self.parse_pats()?;
         let guard = if self.eat_keyword(kw::If) {
-            Some(Guard::If(self.parse_expr()?))
+            Some(self.parse_expr()?)
         } else {
             None
         };
diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index 164fe2f36e1..3f059927e57 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/src/libsyntax/print/pprust.rs
@@ -2653,14 +2653,10 @@ impl<'a> State<'a> {
         self.print_outer_attributes(&arm.attrs)?;
         self.print_pats(&arm.pats)?;
         self.s.space()?;
-        if let Some(ref g) = arm.guard {
-            match g {
-                ast::Guard::If(ref e) => {
-                    self.word_space("if")?;
-                    self.print_expr(e)?;
-                    self.s.space()?;
-                }
-            }
+        if let Some(ref e) = arm.guard {
+            self.word_space("if")?;
+            self.print_expr(e)?;
+            self.s.space()?;
         }
         self.word_space("=>")?;
 
diff --git a/src/libsyntax/visit.rs b/src/libsyntax/visit.rs
index 4d961142ff1..9ec9550f93a 100644
--- a/src/libsyntax/visit.rs
+++ b/src/libsyntax/visit.rs
@@ -826,10 +826,8 @@ pub fn walk_expr<'a, V: Visitor<'a>>(visitor: &mut V, expression: &'a Expr) {
 
 pub fn walk_arm<'a, V: Visitor<'a>>(visitor: &mut V, arm: &'a Arm) {
     walk_list!(visitor, visit_pat, &arm.pats);
-    if let Some(ref g) = &arm.guard {
-        match g {
-            Guard::If(ref e) => visitor.visit_expr(e),
-        }
+    if let Some(ref e) = &arm.guard {
+        visitor.visit_expr(e);
     }
     visitor.visit_expr(&arm.body);
     walk_list!(visitor, visit_attribute, &arm.attrs);