update and add a few tests

compiler/rustc_ast/src/ast.rs

@@ -1814,7 +1814,7 @@ pub enum LitKind {
     /// A byte string (`b"foo"`). Not stored as a symbol because it might be
     /// non-utf8, and symbols only allow utf8 strings.
     ByteStr(Lrc<[u8]>, StrStyle),
-    /// A C String (`c"foo"`).
+    /// A C String (`c"foo"`). Guaranteed only have `\0` in the end.
     CStr(Lrc<[u8]>, StrStyle),
     /// A byte char (`b'f'`).
     Byte(u8),

compiler/rustc_ast/src/util/literal.rs

@@ -181,7 +181,7 @@ impl LitKind {
                     }
                 });
                 error?;
-                buf.push(b'\0');
+                buf.push(0);
                 LitKind::CStr(buf.into(), StrStyle::Cooked)
             }
             token::CStrRaw(n) => {
@@ -204,7 +204,7 @@ impl LitKind {
                     }
                 });
                 error?;
-                buf.push(b'\0');
+                buf.push(0);
                 LitKind::CStr(buf.into(), StrStyle::Raw(n))
             }
             token::Err => LitKind::Err,

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -1,3 +1,4 @@
+use ast::token;
 use rustc_ast as ast;
 use rustc_ast::visit::{self, AssocCtxt, FnCtxt, FnKind, Visitor};
 use rustc_ast::{attr, AssocConstraint, AssocConstraintKind, NodeId};

compiler/rustc_feature/src/active.rs

@@ -313,6 +313,8 @@ declare_features! (
     (active, async_fn_in_trait, "1.66.0", Some(91611), None),
     /// Treat `extern "C"` function as nounwind.
     (active, c_unwind, "1.52.0", Some(74990), None),
+    /// Allows `c"foo"` literals.
+    (active, c_str_literals, "CURRENT_RUSTC_VERSION", Some(105723), None),
     /// Allows using C-variadics.
     (active, c_variadic, "1.34.0", Some(44930), None),
     /// Allows the use of `#[cfg(sanitize = "option")]`; set when -Zsanitizer is used.

compiler/rustc_mir_build/src/build/expr/as_constant.rs

@@ -146,6 +146,12 @@ pub(crate) fn lit_to_mir_constant<'tcx>(
             let id = tcx.allocate_bytes(data);
             ConstValue::Scalar(Scalar::from_pointer(id.into(), &tcx))
         }
+        (ast::LitKind::CStr(data, _), ty::Ref(_, inner_ty, _)) if matches!(inner_ty.kind(), ty::Adt(def, _) if Some(def.did()) == tcx.lang_items().c_str()) =>
+        {
+            let allocation = Allocation::from_bytes_byte_aligned_immutable(data as &[u8]);
+            let allocation = tcx.mk_const_alloc(allocation);
+            ConstValue::Slice { data: allocation, start: 0, end: data.len() }
+        }
         (ast::LitKind::Byte(n), ty::Uint(ty::UintTy::U8)) => {
             ConstValue::Scalar(Scalar::from_uint(*n, Size::from_bytes(1)))
         }

compiler/rustc_span/src/symbol.rs

@@ -441,6 +441,7 @@ symbols! {
         bridge,
         bswap,
         c_str,
+        c_str_literals,
         c_unwind,
         c_variadic,
         call,

tests/ui/rfcs/rfc-3348-c-string-literals/basic.rs

@@ -0,0 +1,7 @@
+// run-pass
+
+#![feature(c_str_literals)]
+
+fn main() {
+    assert_eq!(b"test\0", c"test".to_bytes_with_nul());
+}

tests/ui/rfcs/rfc-3348-c-string-literals/gate.rs

@@ -0,0 +1,7 @@
+fn main() {
+    c"foo";
+    //~^ ERROR: `c".."` literals are experimental
+
+    m!(c"test");
+    //~^ ERROR: `c".."` literals are experimental
+}

tests/ui/rfcs/rfc-3348-c-string-literals/gate.stderr

@@ -0,0 +1,21 @@
+error[E0658]: `c".."` literals are experimental
+  --> $DIR/gate.rs:8:5
+   |
+LL |     c"foo";
+   |     ^^^^^^
+   |
+   = note: see issue #105723 <https://github.com/rust-lang/rust/issues/105723> for more information
+   = help: add `#![feature(c_str_literals)]` to the crate attributes to enable
+
+error[E0658]: `c".."` literals are experimental
+  --> $DIR/gate.rs:11:8
+   |
+LL |     m!(c"test");
+   |        ^^^^^^^
+   |
+   = note: see issue #105723 <https://github.com/rust-lang/rust/issues/105723> for more information
+   = help: add `#![feature(c_str_literals)]` to the crate attributes to enable
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0658`.