Lower Guard Patterns to HIR.

compiler/rustc_ast_lowering/src/pat.rs

@@ -120,8 +120,9 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                             self.lower_range_end(end, e2.is_some()),
                         );
                     }
-                    // FIXME(guard_patterns): lower pattern guards to HIR
-                    PatKind::Guard(inner, _) => pattern = inner,
+                    PatKind::Guard(inner, cond) => {
+                        break hir::PatKind::Guard(self.lower_pat(inner), self.lower_expr(cond));
+                    }
                     PatKind::Slice(pats) => break self.lower_pat_slice(pats),
                     PatKind::Rest => {
                         // If we reach here the `..` pattern is not semantically allowed.

compiler/rustc_hir/src/hir.rs

@@ -1385,7 +1385,7 @@ impl<'hir> Pat<'hir> {
         use PatKind::*;
         match self.kind {
             Wild | Never | Lit(_) | Range(..) | Binding(.., None) | Path(_) | Err(_) => true,
-            Box(s) | Deref(s) | Ref(s, _) | Binding(.., Some(s)) => s.walk_short_(it),
+            Box(s) | Deref(s) | Ref(s, _) | Binding(.., Some(s)) | Guard(s, _) => s.walk_short_(it),
             Struct(_, fields, _) => fields.iter().all(|field| field.pat.walk_short_(it)),
             TupleStruct(_, s, _) | Tuple(s, _) | Or(s) => s.iter().all(|p| p.walk_short_(it)),
             Slice(before, slice, after) => {
@@ -1412,7 +1412,7 @@ impl<'hir> Pat<'hir> {
         use PatKind::*;
         match self.kind {
             Wild | Never | Lit(_) | Range(..) | Binding(.., None) | Path(_) | Err(_) => {}
-            Box(s) | Deref(s) | Ref(s, _) | Binding(.., Some(s)) => s.walk_(it),
+            Box(s) | Deref(s) | Ref(s, _) | Binding(.., Some(s)) | Guard(s, _) => s.walk_(it),
             Struct(_, fields, _) => fields.iter().for_each(|field| field.pat.walk_(it)),
             TupleStruct(_, s, _) | Tuple(s, _) | Or(s) => s.iter().for_each(|p| p.walk_(it)),
             Slice(before, slice, after) => {
@@ -1564,6 +1564,9 @@ pub enum PatKind<'hir> {
     /// A literal.
     Lit(&'hir Expr<'hir>),
 
+    /// A guard pattern (e.g., `x if guard(x)`).
+    Guard(&'hir Pat<'hir>, &'hir Expr<'hir>),
+
     /// A range pattern (e.g., `1..=2` or `1..2`).
     Range(Option<&'hir Expr<'hir>>, Option<&'hir Expr<'hir>>, RangeEnd),
 

compiler/rustc_hir/src/intravisit.rs

@@ -696,6 +696,10 @@ pub fn walk_pat<'v, V: Visitor<'v>>(visitor: &mut V, pattern: &'v Pat<'v>) -> V:
             visit_opt!(visitor, visit_pat, slice_pattern);
             walk_list!(visitor, visit_pat, postpatterns);
         }
+        PatKind::Guard(subpat, condition) => {
+            try_visit!(visitor.visit_pat(subpat));
+            try_visit!(visitor.visit_expr(condition));
+        }
     }
     V::Result::output()
 }

compiler/rustc_hir_analysis/src/check/region.rs

@@ -654,6 +654,7 @@ fn resolve_local<'tcx>(
     ///        | ( ..., P&, ... )
     ///        | ... "|" P& "|" ...
     ///        | box P&
+    ///        | P& if ...
     /// ```
     fn is_binding_pat(pat: &hir::Pat<'_>) -> bool {
         // Note that the code below looks for *explicit* refs only, that is, it won't
@@ -694,7 +695,9 @@ fn resolve_local<'tcx>(
             | PatKind::TupleStruct(_, subpats, _)
             | PatKind::Tuple(subpats, _) => subpats.iter().any(|p| is_binding_pat(p)),
 
-            PatKind::Box(subpat) | PatKind::Deref(subpat) => is_binding_pat(subpat),
+            PatKind::Box(subpat) | PatKind::Deref(subpat) | PatKind::Guard(subpat, _) => {
+                is_binding_pat(subpat)
+            }
 
             PatKind::Ref(_, _)
             | PatKind::Binding(hir::BindingMode(hir::ByRef::No, _), ..)

compiler/rustc_hir_pretty/src/lib.rs

@@ -1999,6 +1999,12 @@ impl<'a> State<'a> {
                 self.commasep(Inconsistent, after, |s, p| s.print_pat(p));
                 self.word("]");
             }
+            PatKind::Guard(inner, cond) => {
+                self.print_pat(inner);
+                self.space();
+                self.word_space("if");
+                self.print_expr(cond);
+            }
             PatKind::Err(_) => {
                 self.popen();
                 self.word("/*ERROR*/");

compiler/rustc_hir_typeck/src/expr.rs

@@ -457,6 +457,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             // Does not constitute a read.
             hir::PatKind::Wild => false,
 
+            // Might not constitute a read, since the condition might be false.
+            hir::PatKind::Guard(_, _) => true,
+
             // This is unnecessarily restrictive when the pattern that doesn't
             // constitute a read is unreachable.
             //

compiler/rustc_hir_typeck/src/expr_use_visitor.rs

@@ -615,6 +615,7 @@ impl<'tcx, Cx: TypeInformationCtxt<'tcx>, D: Delegate<'tcx>> ExprUseVisitor<'tcx
                     | PatKind::Box(_)
                     | PatKind::Deref(_)
                     | PatKind::Ref(..)
+                    | PatKind::Guard(..)
                     | PatKind::Wild
                     | PatKind::Err(_) => {
                         // If the PatKind is Or, Box, or Ref, the decision is made later
@@ -1737,7 +1738,7 @@ impl<'tcx, Cx: TypeInformationCtxt<'tcx>, D: Delegate<'tcx>> ExprUseVisitor<'tcx
                 }
             }
 
-            PatKind::Binding(.., Some(subpat)) => {
+            PatKind::Binding(.., Some(subpat)) | PatKind::Guard(subpat, _) => {
                 self.cat_pattern(place_with_id, subpat, op)?;
             }
 

compiler/rustc_hir_typeck/src/pat.rs

@@ -284,6 +284,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             PatKind::Struct(ref qpath, fields, has_rest_pat) => {
                 self.check_pat_struct(pat, qpath, fields, has_rest_pat, expected, pat_info)
             }
+            PatKind::Guard(pat, cond) => {
+                self.check_pat(pat, expected, pat_info);
+                self.check_expr_has_type_or_error(cond, self.tcx.types.bool, |_| {});
+                expected
+            }
             PatKind::Or(pats) => {
                 for pat in pats {
                     self.check_pat(pat, expected, pat_info);
@@ -422,7 +427,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             // An OR-pattern just propagates to each individual alternative.
             // This is maximally flexible, allowing e.g., `Some(mut x) | &Some(mut x)`.
             // In that example, `Some(mut x)` results in `Peel` whereas `&Some(mut x)` in `Reset`.
-            | PatKind::Or(_) => AdjustMode::Pass,
+            | PatKind::Or(_)
+            // Like or-patterns, guard patterns just propogate to their subpatterns.
+            | PatKind::Guard(..) => AdjustMode::Pass,
         }
     }
 
@@ -901,6 +908,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         PatKind::Struct(..)
                         | PatKind::TupleStruct(..)
                         | PatKind::Or(..)
+                        | PatKind::Guard(..)
                         | PatKind::Tuple(..)
                         | PatKind::Slice(..) => "binding",
 

compiler/rustc_mir_build/src/thir/pattern/mod.rs

@@ -435,6 +435,9 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
 
             hir::PatKind::Or(pats) => PatKind::Or { pats: self.lower_patterns(pats) },
 
+            // FIXME(guard_patterns): implement guard pattern lowering
+            hir::PatKind::Guard(pat, _) => self.lower_pattern(pat).kind,
+
             hir::PatKind::Err(guar) => PatKind::Error(guar),
         };
 

compiler/rustc_passes/src/input_stats.rs

@@ -305,6 +305,7 @@ impl<'v> hir_visit::Visitor<'v> for StatCollector<'v> {
             Deref,
             Ref,
             Lit,
+            Guard,
             Range,
             Slice,
             Err

src/librustdoc/clean/utils.rs

@@ -320,6 +320,7 @@ pub(crate) fn name_from_pat(p: &hir::Pat<'_>) -> Symbol {
             );
             return Symbol::intern("()");
         }
+        PatKind::Guard(p, _) => return name_from_pat(&*p),
         PatKind::Range(..) => return kw::Underscore,
         PatKind::Slice(begin, ref mid, end) => {
             let begin = begin.iter().map(|p| name_from_pat(p).to_string());

src/tools/clippy/clippy_lints/src/equatable_if_let.rs

@@ -55,7 +55,7 @@ fn unary_pattern(pat: &Pat<'_>) -> bool {
         | PatKind::Err(_) => false,
         PatKind::Struct(_, a, etc) => !etc && a.iter().all(|x| unary_pattern(x.pat)),
         PatKind::Tuple(a, etc) | PatKind::TupleStruct(_, a, etc) => etc.as_opt_usize().is_none() && array_rec(a),
-        PatKind::Ref(x, _) | PatKind::Box(x) | PatKind::Deref(x) => unary_pattern(x),
+        PatKind::Ref(x, _) | PatKind::Box(x) | PatKind::Deref(x) | PatKind::Guard(x, _) => unary_pattern(x),
         PatKind::Path(_) | PatKind::Lit(_) => true,
     }
 }

src/tools/clippy/clippy_lints/src/matches/match_same_arms.rs

@@ -254,9 +254,11 @@ impl<'a> NormalizedPat<'a> {
     fn from_pat(cx: &LateContext<'_>, arena: &'a DroplessArena, pat: &'a Pat<'_>) -> Self {
         match pat.kind {
             PatKind::Wild | PatKind::Binding(.., None) => Self::Wild,
-            PatKind::Binding(.., Some(pat)) | PatKind::Box(pat) | PatKind::Deref(pat) | PatKind::Ref(pat, _) => {
-                Self::from_pat(cx, arena, pat)
-            },
+            PatKind::Binding(.., Some(pat))
+            | PatKind::Box(pat)
+            | PatKind::Deref(pat)
+            | PatKind::Ref(pat, _)
+            | PatKind::Guard(pat, _) => Self::from_pat(cx, arena, pat),
             PatKind::Never => Self::Never,
             PatKind::Struct(ref path, fields, _) => {
                 let fields =

src/tools/clippy/clippy_lints/src/matches/single_match.rs

@@ -343,6 +343,10 @@ impl<'a> PatState<'a> {
                 matches!(self, Self::Wild)
             },
 
+            PatKind::Guard(..) => {
+                matches!(self, Self::Wild)
+            }
+
             // Patterns for things which can only contain a single sub-pattern.
             PatKind::Binding(_, _, _, Some(pat)) | PatKind::Ref(pat, _) | PatKind::Box(pat) | PatKind::Deref(pat) => {
                 self.add_pat(cx, pat)

src/tools/clippy/clippy_lints/src/utils/author.rs

@@ -712,6 +712,12 @@ impl<'a, 'tcx> PrintVisitor<'a, 'tcx> {
                 kind!("Ref({pat}, Mutability::{muta:?})");
                 self.pat(pat);
             },
+            PatKind::Guard(pat, cond) => {
+                bind!(self, pat, cond);
+                kind!("Guard({pat}, {cond})");
+                self.pat(pat);
+                self.expr(cond);
+            }
             PatKind::Lit(lit_expr) => {
                 bind!(self, lit_expr);
                 kind!("Lit({lit_expr})");

src/tools/clippy/clippy_utils/src/hir_utils.rs

@@ -1104,6 +1104,10 @@ impl<'a, 'tcx> SpanlessHash<'a, 'tcx> {
                 self.hash_pat(pat);
                 std::mem::discriminant(&mu).hash(&mut self.s);
             },
+            PatKind::Guard(pat, guard) => {
+                self.hash_pat(pat);
+                self.hash_expr(guard);
+            },
             PatKind::Slice(l, m, r) => {
                 for pat in l {
                     self.hash_pat(pat);

src/tools/clippy/clippy_utils/src/lib.rs

@@ -1777,7 +1777,7 @@ pub fn is_refutable(cx: &LateContext<'_>, pat: &Pat<'_>) -> bool {
                 },
             }
         },
-        PatKind::Lit(..) | PatKind::Range(..) | PatKind::Err(_) | PatKind::Deref(_) => true,
+        PatKind::Lit(..) | PatKind::Range(..) | PatKind::Err(_) | PatKind::Deref(_) | PatKind::Guard(..) => true,
     }
 }
 

tests/ui/feature-gates/feature-gate-guard-patterns.rs

@@ -1,3 +1,5 @@
+#![allow(irrefutable_let_patterns)]
+
 fn match_guards_still_work() {
     match 0 {
         0 if guard(0) => {},
@@ -24,11 +26,9 @@ fn other_guards_dont() {
 
     if let (x if guard(x)) = 0 {}
     //~^ ERROR: guard patterns are experimental
-    //~| WARN: irrefutable
 
     while let (x if guard(x)) = 0 {}
     //~^ ERROR: guard patterns are experimental
-    //~| WARN: irrefutable
 
     #[cfg(FALSE)]
     while let (x if guard(x)) = 0 {}

tests/ui/feature-gates/feature-gate-guard-patterns.stderr

@@ -1,5 +1,5 @@
 error: unexpected parentheses surrounding `match` arm pattern
-  --> $DIR/feature-gate-guard-patterns.rs:10:9
+  --> $DIR/feature-gate-guard-patterns.rs:12:9
    |
 LL |         (0 if guard(0)) => {},
    |         ^             ^
@@ -11,7 +11,7 @@ LL +         0 if guard(0) => {},
    |
 
 error[E0425]: cannot find value `x` in this scope
-  --> $DIR/feature-gate-guard-patterns.rs:21:22
+  --> $DIR/feature-gate-guard-patterns.rs:23:22
    |
 LL |     let ((x if guard(x)) | x) = 0;
    |                      ^ not found in this scope
@@ -23,13 +23,13 @@ LL | fn even_as_function_parameters(((x if guard(x), _) | (_, x)): (i32, i32)) {
    |                                             ^
    |
 help: the binding `x` is available in a different scope in the same function
-  --> $DIR/feature-gate-guard-patterns.rs:21:11
+  --> $DIR/feature-gate-guard-patterns.rs:23:11
    |
 LL |     let ((x if guard(x)) | x) = 0;
    |           ^
 
 error[E0658]: guard patterns are experimental
-  --> $DIR/feature-gate-guard-patterns.rs:16:15
+  --> $DIR/feature-gate-guard-patterns.rs:18:15
    |
 LL |         (0 if guard(0)) | 1 => {},
    |               ^^^^^^^^
@@ -40,7 +40,7 @@ LL |         (0 if guard(0)) | 1 => {},
    = help: consider using match arm guards
 
 error[E0658]: guard patterns are experimental
-  --> $DIR/feature-gate-guard-patterns.rs:21:16
+  --> $DIR/feature-gate-guard-patterns.rs:23:16
    |
 LL |     let ((x if guard(x)) | x) = 0;
    |                ^^^^^^^^
@@ -51,7 +51,7 @@ LL |     let ((x if guard(x)) | x) = 0;
    = help: consider using match arm guards
 
 error[E0658]: guard patterns are experimental
-  --> $DIR/feature-gate-guard-patterns.rs:25:18
+  --> $DIR/feature-gate-guard-patterns.rs:27:18
    |
 LL |     if let (x if guard(x)) = 0 {}
    |                  ^^^^^^^^
@@ -62,7 +62,7 @@ LL |     if let (x if guard(x)) = 0 {}
    = help: consider using match arm guards
 
 error[E0658]: guard patterns are experimental
-  --> $DIR/feature-gate-guard-patterns.rs:29:21
+  --> $DIR/feature-gate-guard-patterns.rs:30:21
    |
 LL |     while let (x if guard(x)) = 0 {}
    |                     ^^^^^^^^
@@ -94,26 +94,7 @@ LL | fn even_as_function_parameters(((x if guard(x), _) | (_, x)): (i32, i32)) {
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
    = help: consider using match arm guards
 
-warning: irrefutable `if let` pattern
-  --> $DIR/feature-gate-guard-patterns.rs:25:8
-   |
-LL |     if let (x if guard(x)) = 0 {}
-   |        ^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: this pattern will always match, so the `if let` is useless
-   = help: consider replacing the `if let` with a `let`
-   = note: `#[warn(irrefutable_let_patterns)]` on by default
-
-warning: irrefutable `while let` pattern
-  --> $DIR/feature-gate-guard-patterns.rs:29:11
-   |
-LL |     while let (x if guard(x)) = 0 {}
-   |           ^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: this pattern will always match, so the loop will never exit
-   = help: consider instead using a `loop { ... }` with a `let` inside it
-
-error: aborting due to 9 previous errors; 2 warnings emitted
+error: aborting due to 9 previous errors
 
 Some errors have detailed explanations: E0425, E0658.
 For more information about an error, try `rustc --explain E0425`.