Feature gate or patterns in const contexts

Author: matthewjasper

src/librustc_passes/check_const.rs

@@ -27,13 +27,15 @@ use std::fmt;
 enum NonConstExpr {
     Loop(hir::LoopSource),
     Match(hir::MatchSource),
+    OrPattern,
 }
 
 impl NonConstExpr {
-    fn name(self) -> &'static str {
+    fn name(self) -> String {
         match self {
-            Self::Loop(src) => src.name(),
-            Self::Match(src) => src.name(),
+            Self::Loop(src) => format!("`{}`", src.name()),
+            Self::Match(src) => format!("`{}`", src.name()),
+            Self::OrPattern => format!("or-pattern"),
         }
     }
 
@@ -44,7 +46,8 @@ impl NonConstExpr {
         let gates: &[_] = match self {
             Self::Match(Normal)
             | Self::Match(IfDesugar { .. })
-            | Self::Match(IfLetDesugar { .. }) => &[sym::const_if_match],
+            | Self::Match(IfLetDesugar { .. })
+            | Self::OrPattern => &[sym::const_if_match],
 
             Self::Loop(Loop) => &[sym::const_loop],
 
@@ -144,7 +147,7 @@ impl<'tcx> CheckConstVisitor<'tcx> {
         let const_kind = self
             .const_kind
             .expect("`const_check_violated` may only be called inside a const context");
-        let msg = format!("`{}` is not allowed in a `{}`", expr.name(), const_kind);
+        let msg = format!("{} is not allowed in a `{}`", expr.name(), const_kind);
 
         let required_gates = required_gates.unwrap_or(&[]);
         let missing_gates: Vec<_> =
@@ -211,6 +214,15 @@ impl<'tcx> Visitor<'tcx> for CheckConstVisitor<'tcx> {
         self.recurse_into(kind, |this| hir::intravisit::walk_body(this, body));
     }
 
+    fn visit_pat(&mut self, p: &'tcx hir::Pat) {
+        if self.const_kind.is_some() {
+            if let hir::PatKind::Or { .. } = p.kind {
+                self.const_check_violated(NonConstExpr::OrPattern, p.span);
+            }
+        }
+        hir::intravisit::walk_pat(self, p)
+    }
+
     fn visit_expr(&mut self, e: &'tcx hir::Expr) {
         match &e.kind {
             // Skip the following checks if we are not currently in a const context.

src/test/ui/or-patterns/feature-gate-const-fn.rs

@@ -0,0 +1,36 @@
+#![feature(or_patterns)]
+#![allow(incomplete_features)]
+
+const fn foo((Ok(a) | Err(a)): Result<i32, i32>) {
+    //~^ ERROR or-pattern is not allowed in a `const fn`
+    let x = Ok(3);
+    let Ok(y) | Err(y) = x;
+    //~^ ERROR or-pattern is not allowed in a `const fn`
+}
+
+const X: () = {
+    let x = Ok(3);
+    let Ok(y) | Err(y) = x;
+    //~^ ERROR or-pattern is not allowed in a `const`
+};
+
+static Y: () = {
+    let x = Ok(3);
+    let Ok(y) | Err(y) = x;
+    //~^ ERROR or-pattern is not allowed in a `static`
+};
+
+static mut Z: () = {
+    let x = Ok(3);
+    let Ok(y) | Err(y) = x;
+    //~^ ERROR or-pattern is not allowed in a `static mut`
+};
+
+fn main() {
+    let _: [(); {
+        let x = Ok(3);
+        let Ok(y) | Err(y) = x;
+        //~^ ERROR or-pattern is not allowed in a `const`
+        2
+    }];
+}

src/test/ui/or-patterns/feature-gate-const-fn.stderr

@@ -0,0 +1,57 @@
+error[E0658]: or-pattern is not allowed in a `const fn`
+  --> $DIR/feature-gate-const-fn.rs:4:15
+   |
+LL | const fn foo((Ok(a) | Err(a)): Result<i32, i32>) {
+   |               ^^^^^^^^^^^^^^
+   |
+   = note: for more information, see https://github.com/rust-lang/rust/issues/49146
+   = help: add `#![feature(const_if_match)]` to the crate attributes to enable
+
+error[E0658]: or-pattern is not allowed in a `const fn`
+  --> $DIR/feature-gate-const-fn.rs:7:9
+   |
+LL |     let Ok(y) | Err(y) = x;
+   |         ^^^^^^^^^^^^^^
+   |
+   = note: for more information, see https://github.com/rust-lang/rust/issues/49146
+   = help: add `#![feature(const_if_match)]` to the crate attributes to enable
+
+error[E0658]: or-pattern is not allowed in a `const`
+  --> $DIR/feature-gate-const-fn.rs:13:9
+   |
+LL |     let Ok(y) | Err(y) = x;
+   |         ^^^^^^^^^^^^^^
+   |
+   = note: for more information, see https://github.com/rust-lang/rust/issues/49146
+   = help: add `#![feature(const_if_match)]` to the crate attributes to enable
+
+error[E0658]: or-pattern is not allowed in a `static`
+  --> $DIR/feature-gate-const-fn.rs:19:9
+   |
+LL |     let Ok(y) | Err(y) = x;
+   |         ^^^^^^^^^^^^^^
+   |
+   = note: for more information, see https://github.com/rust-lang/rust/issues/49146
+   = help: add `#![feature(const_if_match)]` to the crate attributes to enable
+
+error[E0658]: or-pattern is not allowed in a `static mut`
+  --> $DIR/feature-gate-const-fn.rs:25:9
+   |
+LL |     let Ok(y) | Err(y) = x;
+   |         ^^^^^^^^^^^^^^
+   |
+   = note: for more information, see https://github.com/rust-lang/rust/issues/49146
+   = help: add `#![feature(const_if_match)]` to the crate attributes to enable
+
+error[E0658]: or-pattern is not allowed in a `const`
+  --> $DIR/feature-gate-const-fn.rs:32:13
+   |
+LL |         let Ok(y) | Err(y) = x;
+   |             ^^^^^^^^^^^^^^
+   |
+   = note: for more information, see https://github.com/rust-lang/rust/issues/49146
+   = help: add `#![feature(const_if_match)]` to the crate attributes to enable
+
+error: aborting due to 6 previous errors
+
+For more information about this error, try `rustc --explain E0658`.