Auto merge of #84571 - jedel1043:issue-49804-impl, r=petrochenkov

Parse unnamed fields of struct and union type

Added the `unnamed_fields` feature gate.

This is a prototype of [RFC 2102](https://github.com/rust-lang/rust/issues/49804), so any suggestions are greatly appreciated.

r? `@petrochenkov`

4 files changed, 365 insertions, 0 deletions

diff --git a/src/test/ui/feature-gates/feature-gate-unnamed_fields.rs b/src/test/ui/feature-gates/feature-gate-unnamed_fields.rs
new file mode 100644
index 00000000000..bd815dbcc92
--- /dev/null
+++ b/src/test/ui/feature-gates/feature-gate-unnamed_fields.rs
@@ -0,0 +1,27 @@
+struct Foo {
+    foo: u8,
+    _: union { //~ ERROR unnamed fields are not yet fully implemented [E0658]
+    //~^ ERROR unnamed fields are not yet fully implemented [E0658]
+    //~| ERROR anonymous unions are unimplemented
+        bar: u8,
+        baz: u16
+    }
+}
+
+union Bar {
+    foobar: u8,
+    _: struct { //~ ERROR unnamed fields are not yet fully implemented [E0658]
+    //~^ ERROR unnamed fields are not yet fully implemented [E0658]
+    //~| ERROR anonymous structs are unimplemented
+    //~| ERROR unions may not contain fields that need dropping [E0740]
+        foobaz: u8,
+        barbaz: u16
+    }
+}
+
+struct S;
+struct Baz {
+    _: S //~ ERROR unnamed fields are not yet fully implemented [E0658]
+}
+
+fn main(){}
diff --git a/src/test/ui/feature-gates/feature-gate-unnamed_fields.stderr b/src/test/ui/feature-gates/feature-gate-unnamed_fields.stderr
new file mode 100644
index 00000000000..4f3ab85c987
--- /dev/null
+++ b/src/test/ui/feature-gates/feature-gate-unnamed_fields.stderr
@@ -0,0 +1,111 @@
+error[E0658]: unnamed fields are not yet fully implemented
+  --> $DIR/feature-gate-unnamed_fields.rs:3:5
+   |
+LL |     _: union {
+   |     ^
+   |
+   = note: see issue #49804 <https://github.com/rust-lang/rust/issues/49804> for more information
+   = help: add `#![feature(unnamed_fields)]` to the crate attributes to enable
+
+error[E0658]: unnamed fields are not yet fully implemented
+  --> $DIR/feature-gate-unnamed_fields.rs:3:8
+   |
+LL |       _: union {
+   |  ________^
+LL | |
+LL | |
+LL | |         bar: u8,
+LL | |         baz: u16
+LL | |     }
+   | |_____^
+   |
+   = note: see issue #49804 <https://github.com/rust-lang/rust/issues/49804> for more information
+   = help: add `#![feature(unnamed_fields)]` to the crate attributes to enable
+
+error[E0658]: unnamed fields are not yet fully implemented
+  --> $DIR/feature-gate-unnamed_fields.rs:13:5
+   |
+LL |     _: struct {
+   |     ^
+   |
+   = note: see issue #49804 <https://github.com/rust-lang/rust/issues/49804> for more information
+   = help: add `#![feature(unnamed_fields)]` to the crate attributes to enable
+
+error[E0658]: unnamed fields are not yet fully implemented
+  --> $DIR/feature-gate-unnamed_fields.rs:13:8
+   |
+LL |       _: struct {
+   |  ________^
+LL | |
+LL | |
+LL | |
+LL | |         foobaz: u8,
+LL | |         barbaz: u16
+LL | |     }
+   | |_____^
+   |
+   = note: see issue #49804 <https://github.com/rust-lang/rust/issues/49804> for more information
+   = help: add `#![feature(unnamed_fields)]` to the crate attributes to enable
+
+error[E0658]: unnamed fields are not yet fully implemented
+  --> $DIR/feature-gate-unnamed_fields.rs:24:5
+   |
+LL |     _: S
+   |     ^
+   |
+   = note: see issue #49804 <https://github.com/rust-lang/rust/issues/49804> for more information
+   = help: add `#![feature(unnamed_fields)]` to the crate attributes to enable
+
+error: anonymous unions are unimplemented
+  --> $DIR/feature-gate-unnamed_fields.rs:3:8
+   |
+LL |       _: union {
+   |  ________^
+LL | |
+LL | |
+LL | |         bar: u8,
+LL | |         baz: u16
+LL | |     }
+   | |_____^
+
+error: anonymous structs are unimplemented
+  --> $DIR/feature-gate-unnamed_fields.rs:13:8
+   |
+LL |       _: struct {
+   |  ________^
+LL | |
+LL | |
+LL | |
+LL | |         foobaz: u8,
+LL | |         barbaz: u16
+LL | |     }
+   | |_____^
+
+error[E0740]: unions may not contain fields that need dropping
+  --> $DIR/feature-gate-unnamed_fields.rs:13:5
+   |
+LL | /     _: struct {
+LL | |
+LL | |
+LL | |
+LL | |         foobaz: u8,
+LL | |         barbaz: u16
+LL | |     }
+   | |_____^
+   |
+note: `std::mem::ManuallyDrop` can be used to wrap the type
+  --> $DIR/feature-gate-unnamed_fields.rs:13:5
+   |
+LL | /     _: struct {
+LL | |
+LL | |
+LL | |
+LL | |         foobaz: u8,
+LL | |         barbaz: u16
+LL | |     }
+   | |_____^
+
+error: aborting due to 8 previous errors
+
+Some errors have detailed explanations: E0658, E0740.
+For more information about an error, try `rustc --explain E0658`.
diff --git a/src/test/ui/unnamed_fields/restrict_anonymous.rs b/src/test/ui/unnamed_fields/restrict_anonymous.rs
new file mode 100644
index 00000000000..99637d11053
--- /dev/null
+++ b/src/test/ui/unnamed_fields/restrict_anonymous.rs
@@ -0,0 +1,52 @@
+#![allow(incomplete_features)]
+#![feature(unnamed_fields)]
+
+fn f() -> struct { field: u8 } {} //~ ERROR anonymous structs are not allowed outside of unnamed struct or union fields
+//~^ ERROR anonymous structs are unimplemented
+
+fn f2(a: struct { field: u8 } ) {} //~ ERROR anonymous structs are not allowed outside of unnamed struct or union fields
+//~^ ERROR anonymous structs are unimplemented
+
+union G {
+    field: struct { field: u8 } //~ ERROR anonymous structs are not allowed outside of unnamed struct or union fields
+    //~^ ERROR anonymous structs are unimplemented
+}
+//~| ERROR unions may not contain fields that need dropping [E0740]
+
+struct H { _: u8 } // Should error after hir checks
+
+struct I(struct { field: u8 }, u8); //~ ERROR anonymous structs are not allowed outside of unnamed struct or union fields
+//~^ ERROR anonymous structs are unimplemented
+
+enum J {
+    K(struct { field: u8 }), //~ ERROR anonymous structs are not allowed outside of unnamed struct or union fields
+    //~^ ERROR anonymous structs are unimplemented
+    L {
+        _ : struct { field: u8 } //~ ERROR anonymous structs are not allowed outside of unnamed struct or union fields
+        //~^ ERROR anonymous fields are not allowed outside of structs or unions
+        //~| ERROR anonymous structs are unimplemented
+    },
+    M {
+        _ : u8 //~ ERROR anonymous fields are not allowed outside of structs or unions
+    }
+}
+
+static M: union { field: u8 } = 0; //~ ERROR anonymous unions are not allowed outside of unnamed struct or union fields
+//~^ ERROR anonymous unions are unimplemented
+
+type N = union { field: u8 }; //~ ERROR anonymous unions are not allowed outside of unnamed struct or union fields
+//~^ ERROR anonymous unions are unimplemented
+
+fn main() {
+    const O: struct { field: u8 } = 0; //~ ERROR anonymous structs are not allowed outside of unnamed struct or union fields
+    //~^ ERROR anonymous structs are unimplemented
+
+    let p: [struct { field: u8 }; 1]; //~ ERROR anonymous structs are not allowed outside of unnamed struct or union fields
+    //~^ ERROR anonymous structs are unimplemented
+
+    let q: (struct { field: u8 }, u8); //~ ERROR anonymous structs are not allowed outside of unnamed struct or union fields
+    //~^ ERROR anonymous structs are unimplemented
+
+    let cl = || -> struct { field: u8 } {}; //~ ERROR anonymous structs are not allowed outside of unnamed struct or union fields
+    //~^ ERROR anonymous structs are unimplemented
+}
diff --git a/src/test/ui/unnamed_fields/restrict_anonymous.stderr b/src/test/ui/unnamed_fields/restrict_anonymous.stderr
new file mode 100644
index 00000000000..efcf544fde4
--- /dev/null
+++ b/src/test/ui/unnamed_fields/restrict_anonymous.stderr
@@ -0,0 +1,175 @@
+error: anonymous structs are not allowed outside of unnamed struct or union fields
+  --> $DIR/restrict_anonymous.rs:4:11
+   |
+LL | fn f() -> struct { field: u8 } {}
+   |           ^^^^^^^^^^^^^^^^^^^^ anonymous struct declared here
+
+error: anonymous structs are not allowed outside of unnamed struct or union fields
+  --> $DIR/restrict_anonymous.rs:7:10
+   |
+LL | fn f2(a: struct { field: u8 } ) {}
+   |          ^^^^^^^^^^^^^^^^^^^^ anonymous struct declared here
+
+error: anonymous structs are not allowed outside of unnamed struct or union fields
+  --> $DIR/restrict_anonymous.rs:11:12
+   |
+LL |     field: struct { field: u8 }
+   |            ^^^^^^^^^^^^^^^^^^^^ anonymous struct declared here
+
+error: anonymous structs are not allowed outside of unnamed struct or union fields
+  --> $DIR/restrict_anonymous.rs:18:10
+   |
+LL | struct I(struct { field: u8 }, u8);
+   |          ^^^^^^^^^^^^^^^^^^^^ anonymous struct declared here
+
+error: anonymous structs are not allowed outside of unnamed struct or union fields
+  --> $DIR/restrict_anonymous.rs:22:7
+   |
+LL |     K(struct { field: u8 }),
+   |       ^^^^^^^^^^^^^^^^^^^^ anonymous struct declared here
+
+error: anonymous fields are not allowed outside of structs or unions
+  --> $DIR/restrict_anonymous.rs:25:9
+   |
+LL |         _ : struct { field: u8 }
+   |         -^^^^^^^^^^^^^^^^^^^^^^^
+   |         |
+   |         anonymous field declared here
+
+error: anonymous structs are not allowed outside of unnamed struct or union fields
+  --> $DIR/restrict_anonymous.rs:25:13
+   |
+LL |         _ : struct { field: u8 }
+   |             ^^^^^^^^^^^^^^^^^^^^ anonymous struct declared here
+
+error: anonymous fields are not allowed outside of structs or unions
+  --> $DIR/restrict_anonymous.rs:30:9
+   |
+LL |         _ : u8
+   |         -^^^^^
+   |         |
+   |         anonymous field declared here
+
+error: anonymous unions are not allowed outside of unnamed struct or union fields
+  --> $DIR/restrict_anonymous.rs:34:11
+   |
+LL | static M: union { field: u8 } = 0;
+   |           ^^^^^^^^^^^^^^^^^^^ anonymous union declared here
+
+error: anonymous unions are not allowed outside of unnamed struct or union fields
+  --> $DIR/restrict_anonymous.rs:37:10
+   |
+LL | type N = union { field: u8 };
+   |          ^^^^^^^^^^^^^^^^^^^ anonymous union declared here
+
+error: anonymous structs are not allowed outside of unnamed struct or union fields
+  --> $DIR/restrict_anonymous.rs:41:14
+   |
+LL |     const O: struct { field: u8 } = 0;
+   |              ^^^^^^^^^^^^^^^^^^^^ anonymous struct declared here
+
+error: anonymous structs are not allowed outside of unnamed struct or union fields
+  --> $DIR/restrict_anonymous.rs:44:13
+   |
+LL |     let p: [struct { field: u8 }; 1];
+   |             ^^^^^^^^^^^^^^^^^^^^ anonymous struct declared here
+
+error: anonymous structs are not allowed outside of unnamed struct or union fields
+  --> $DIR/restrict_anonymous.rs:47:13
+   |
+LL |     let q: (struct { field: u8 }, u8);
+   |             ^^^^^^^^^^^^^^^^^^^^ anonymous struct declared here
+
+error: anonymous structs are not allowed outside of unnamed struct or union fields
+  --> $DIR/restrict_anonymous.rs:50:20
+   |
+LL |     let cl = || -> struct { field: u8 } {};
+   |                    ^^^^^^^^^^^^^^^^^^^^ anonymous struct declared here
+
+error: anonymous structs are unimplemented
+  --> $DIR/restrict_anonymous.rs:4:11
+   |
+LL | fn f() -> struct { field: u8 } {}
+   |           ^^^^^^^^^^^^^^^^^^^^
+
+error: anonymous structs are unimplemented
+  --> $DIR/restrict_anonymous.rs:7:10
+   |
+LL | fn f2(a: struct { field: u8 } ) {}
+   |          ^^^^^^^^^^^^^^^^^^^^
+
+error: anonymous structs are unimplemented
+  --> $DIR/restrict_anonymous.rs:11:12
+   |
+LL |     field: struct { field: u8 }
+   |            ^^^^^^^^^^^^^^^^^^^^
+
+error: anonymous structs are unimplemented
+  --> $DIR/restrict_anonymous.rs:18:10
+   |
+LL | struct I(struct { field: u8 }, u8);
+   |          ^^^^^^^^^^^^^^^^^^^^
+
+error: anonymous structs are unimplemented
+  --> $DIR/restrict_anonymous.rs:22:7
+   |
+LL |     K(struct { field: u8 }),
+   |       ^^^^^^^^^^^^^^^^^^^^
+
+error: anonymous structs are unimplemented
+  --> $DIR/restrict_anonymous.rs:25:13
+   |
+LL |         _ : struct { field: u8 }
+   |             ^^^^^^^^^^^^^^^^^^^^
+
+error: anonymous unions are unimplemented
+  --> $DIR/restrict_anonymous.rs:34:11
+   |
+LL | static M: union { field: u8 } = 0;
+   |           ^^^^^^^^^^^^^^^^^^^
+
+error: anonymous unions are unimplemented
+  --> $DIR/restrict_anonymous.rs:37:10
+   |
+LL | type N = union { field: u8 };
+   |          ^^^^^^^^^^^^^^^^^^^
+
+error: anonymous structs are unimplemented
+  --> $DIR/restrict_anonymous.rs:44:13
+   |
+LL |     let p: [struct { field: u8 }; 1];
+   |             ^^^^^^^^^^^^^^^^^^^^
+
+error: anonymous structs are unimplemented
+  --> $DIR/restrict_anonymous.rs:47:13
+   |
+LL |     let q: (struct { field: u8 }, u8);
+   |             ^^^^^^^^^^^^^^^^^^^^
+
+error: anonymous structs are unimplemented
+  --> $DIR/restrict_anonymous.rs:50:20
+   |
+LL |     let cl = || -> struct { field: u8 } {};
+   |                    ^^^^^^^^^^^^^^^^^^^^
+
+error: anonymous structs are unimplemented
+  --> $DIR/restrict_anonymous.rs:41:14
+   |
+LL |     const O: struct { field: u8 } = 0;
+   |              ^^^^^^^^^^^^^^^^^^^^
+
+error[E0740]: unions may not contain fields that need dropping
+  --> $DIR/restrict_anonymous.rs:11:5
+   |
+LL |     field: struct { field: u8 }
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: `std::mem::ManuallyDrop` can be used to wrap the type
+  --> $DIR/restrict_anonymous.rs:11:5
+   |
+LL |     field: struct { field: u8 }
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 27 previous errors
+
+For more information about this error, try `rustc --explain E0740`.