Expand potential inner Or pattern for THIR

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

@@ -453,7 +453,17 @@ impl<'p, 'tcx> Matrix<'p, 'tcx> {
     /// expands it.
     fn push(&mut self, row: PatStack<'p, 'tcx>) {
         if !row.is_empty() && row.head().is_or_pat() {
-            self.patterns.extend(row.expand_or_pat());
+            let pats = row.expand_or_pat();
+            let mut no_inner_or = true;
+            for pat in pats {
+                if !pat.is_empty() && pat.head().is_or_pat() {
+                    self.patterns.extend(pat.expand_or_pat());
+                    no_inner_or = false;
+                }
+            }
+            if no_inner_or {
+                self.patterns.extend(row.expand_or_pat());
+            }
         } else {
             self.patterns.push(row);
         }

src/test/ui/or-patterns/inner-or-pat-2.rs

@@ -0,0 +1,13 @@
+#[allow(unused_variables)]
+#[allow(unused_parens)]
+fn main() {
+    let x = "foo";
+    match x {
+        x @ ((("h" | "ho" | "yo" | ("dude" | "w")) | () | "nop") | ("hey" | "gg")) |
+        //~^ ERROR mismatched types
+        x @ ("black" | "pink") |
+        x @ ("red" | "blue") => {
+        }
+        _ => (),
+    }
+}

src/test/ui/or-patterns/inner-or-pat-2.stderr

@@ -0,0 +1,11 @@
+error[E0308]: mismatched types
+  --> $DIR/inner-or-pat-2.rs:6:54
+   |
+LL |     match x {
+   |           - this expression has type `&str`
+LL |         x @ ((("h" | "ho" | "yo" | ("dude" | "w")) | () | "nop") | ("hey" | "gg")) |
+   |                                                      ^^ expected `str`, found `()`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0308`.

src/test/ui/or-patterns/inner-or-pat-3.rs

@@ -0,0 +1,15 @@
+// run-pass
+
+#[allow(unreachable_patterns)]
+#[allow(unused_variables)]
+#[allow(unused_parens)]
+fn main() {
+    let x = "foo";
+
+    match x {
+        x @ ("foo" | "bar") |
+        (x @ "red" | (x @ "blue" | x @ "red")) => {
+        }
+        _ => (),
+    }
+}

src/test/ui/or-patterns/inner-or-pat-4.rs

@@ -0,0 +1,13 @@
+#[allow(unused_variables)]
+#[allow(unused_parens)]
+fn main() {
+    let x = "foo";
+
+    match x {
+        x @ ("foo" | "bar") |
+        (x @ "red" | (x @ "blue" |  "red")) => {
+        //~^ variable `x` is not bound in all patterns
+        }
+        _ => (),
+    }
+}

src/test/ui/or-patterns/inner-or-pat-4.stderr

@@ -0,0 +1,11 @@
+error[E0408]: variable `x` is not bound in all patterns
+  --> $DIR/inner-or-pat-4.rs:8:37
+   |
+LL |         (x @ "red" | (x @ "blue" |  "red")) => {
+   |                       -             ^^^^^ pattern doesn't bind `x`
+   |                       |
+   |                       variable not in all patterns
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0408`.

src/test/ui/or-patterns/inner-or-pat.rs

@@ -0,0 +1,14 @@
+// run-pass
+
+#[allow(unused_variables)]
+#[allow(unused_parens)]
+fn main() {
+    let x = "foo";
+    match x {
+        x @ ((("h" | "ho" | "yo" | ("dude" | "w")) | "no" | "nop") | ("hey" | "gg")) |
+        x @ ("black" | "pink") |
+        x @ ("red" | "blue") => {
+        }
+        _ => (),
+    }
+}