Auto merge of #77124 - spastorino:const-exprs-rfc-2920, r=oli-obk

Implement const expressions and patterns (RFC 2920)

cc `@ecstatic-morse` `@lcnr` `@oli-obk` `@petrochenkov`

src/test/ui/feature-gate-inline_const.rs

@@ -0,0 +1,6 @@
+fn main() {
+    let _ = const {
+        //~^ ERROR inline-const is experimental [E0658]
+        true
+    };
+}

src/test/ui/feature-gate-inline_const.stderr

@@ -0,0 +1,12 @@
+error[E0658]: inline-const is experimental
+  --> $DIR/feature-gate-inline_const.rs:2:13
+   |
+LL |     let _ = const {
+   |             ^^^^^
+   |
+   = note: see issue #76001 <https://github.com/rust-lang/rust/issues/76001> for more information
+   = help: add `#![feature(inline_const)]` to the crate attributes to enable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0658`.

src/test/ui/inline-const/const-expr-array-init.rs

@@ -0,0 +1,10 @@
+// build-pass
+
+#![allow(incomplete_features)]
+#![feature(inline_const)]
+
+use std::cell::Cell;
+
+fn main() {
+    let _x = [const { Cell::new(0) }; 20];
+}

src/test/ui/inline-const/const-expr-basic.rs

@@ -0,0 +1,14 @@
+// run-pass
+
+#![allow(incomplete_features)]
+#![feature(inline_const)]
+fn foo() -> i32 {
+    const {
+        let x = 5 + 10;
+        x / 3
+    }
+}
+
+fn main() {
+    assert_eq!(5, foo());
+}

src/test/ui/inline-const/const-expr-reference.rs

@@ -0,0 +1,15 @@
+// run-pass
+
+#![allow(incomplete_features)]
+#![feature(inline_const)]
+
+const fn bar() -> i32 {
+    const {
+        2 + 3
+    }
+}
+
+fn main() {
+    let x: &'static i32 = &const{bar()};
+    assert_eq!(&5, x);
+}

src/test/ui/inline-const/const-match-pat.rs

@@ -0,0 +1,21 @@
+// run-pass
+
+#![allow(incomplete_features)]
+#![feature(inline_const)]
+const MMIO_BIT1: u8 = 4;
+const MMIO_BIT2: u8 = 5;
+
+fn main() {
+    let s = match read_mmio() {
+        0 => "FOO",
+        const { 1 << MMIO_BIT1 } => "BAR",
+        const { 1 << MMIO_BIT2 } => "BAZ",
+        _ => unreachable!(),
+    };
+
+    assert_eq!("BAZ", s);
+}
+
+fn read_mmio() -> i32 {
+    1 << 5
+}

src/test/ui/parser/issue-66357-unexpected-unreachable.rs

@@ -13,4 +13,4 @@
 
 fn f() { |[](* }
 //~^ ERROR expected one of `,` or `:`, found `(`
-//~| ERROR expected one of `&`, `(`, `)`, `-`, `...`, `..=`, `..`, `[`, `_`, `box`, `mut`, `ref`, `|`, identifier, or path, found `*`
+//~| ERROR expected one of `&`, `(`, `)`, `-`, `...`, `..=`, `..`, `[`, `_`, `box`, `const`, `mut`, `ref`, `|`, identifier, or path, found `*`

src/test/ui/parser/issue-66357-unexpected-unreachable.stderr

@@ -4,7 +4,7 @@ error: expected one of `,` or `:`, found `(`
 LL | fn f() { |[](* }
    |             ^ expected one of `,` or `:`
 
-error: expected one of `&`, `(`, `)`, `-`, `...`, `..=`, `..`, `[`, `_`, `box`, `mut`, `ref`, `|`, identifier, or path, found `*`
+error: expected one of `&`, `(`, `)`, `-`, `...`, `..=`, `..`, `[`, `_`, `box`, `const`, `mut`, `ref`, `|`, identifier, or path, found `*`
   --> $DIR/issue-66357-unexpected-unreachable.rs:14:14
    |
 LL | fn f() { |[](* }