diff mbox series

[v1,19/28] rust: str: add `c_str!` macro

Message ID 20221110164152.26136-20-ojeda@kernel.org
State New
Headers
Series Rust core additions |

Commit Message

Miguel Ojeda Nov. 10, 2022, 4:41 p.m. UTC 
  From: Gary Guo <gary@garyguo.net>

Add `c_str!`, which is a convenience macro that creates a new `CStr`
from a string literal.

It is designed to be similar to a `str` in usage, and it is usable
in const contexts, for instance:

    const X: &CStr = c_str!("Example");

Co-developed-by: Alex Gaynor <alex.gaynor@gmail.com>
Signed-off-by: Alex Gaynor <alex.gaynor@gmail.com>
Signed-off-by: Gary Guo <gary@garyguo.net>
[Reworded, adapted for upstream and applied latest changes]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
 rust/kernel/str.rs | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

Comments

Gary Guo Nov. 14, 2022, 2:39 p.m. UTC | #1 
On Thu, 10 Nov 2022 17:41:31 +0100
Miguel Ojeda <ojeda@kernel.org> wrote:

> From: Gary Guo <gary@garyguo.net>
> 
> Add `c_str!`, which is a convenience macro that creates a new `CStr`
> from a string literal.
> 
> It is designed to be similar to a `str` in usage, and it is usable
> in const contexts, for instance:
> 
>     const X: &CStr = c_str!("Example");
> 
> Co-developed-by: Alex Gaynor <alex.gaynor@gmail.com>
> Signed-off-by: Alex Gaynor <alex.gaynor@gmail.com>
> Signed-off-by: Gary Guo <gary@garyguo.net>
> [Reworded, adapted for upstream and applied latest changes]
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
> ---
>  rust/kernel/str.rs | 32 ++++++++++++++++++++++++++++++++
>  1 file changed, 32 insertions(+)
> 
> diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
> index 3ed685cb5a3c..3fb73b888dce 100644
> --- a/rust/kernel/str.rs
> +++ b/rust/kernel/str.rs
> @@ -128,6 +128,18 @@ impl CStr {
>          Ok(unsafe { Self::from_bytes_with_nul_unchecked(bytes) })
>      }
>  
> +    /// Creates a [`CStr`] from a `[u8]`, panic if input is not valid.
> +    ///
> +    /// This function is only meant to be used by `c_str!` macro, so
> +    /// crates using `c_str!` macro don't have to enable `const_panic` feature.

I wrote this code when `const_panic` was not yet stable. Now we have
stable const panic this function could be removed.

> +    #[doc(hidden)]
> +    pub const fn from_bytes_with_nul_unwrap(bytes: &[u8]) -> &Self {
> +        match Self::from_bytes_with_nul(bytes) {
> +            Ok(v) => v,
> +            Err(_) => panic!("string contains interior NUL"),
> +        }
> +    }
> +
>      /// Creates a [`CStr`] from a `[u8]` without performing any additional
>      /// checks.
>      ///
> @@ -321,6 +333,26 @@ where
>      }
>  }
>  
> +/// Creates a new [`CStr`] from a string literal.
> +///
> +/// The string literal should not contain any `NUL` bytes.
> +///
> +/// # Examples
> +///
> +/// ```
> +/// # use kernel::c_str;
> +/// # use kernel::str::CStr;
> +/// const MY_CSTR: &CStr = c_str!("My awesome CStr!");
> +/// ```
> +#[macro_export]
> +macro_rules! c_str {
> +    ($str:expr) => {{
> +        const S: &str = concat!($str, "\0");
> +        const C: &$crate::str::CStr = $crate::str::CStr::from_bytes_with_nul_unwrap(S.as_bytes());
> +        C
> +    }};
> +}

+#[macro_export]
+macro_rules! c_str {
+    ($str:expr) => {{
+        const S: &str = concat!($str, "\0");
+        const C: &$crate::str::CStr = match $crate::str::CStr::from_bytes_with_nul(S.as_bytes()) {
+            Ok(v) => v,
+            Err(_) => panic!("string contains interior NUL"),
+        };
+        C
+    }};
+}

> +
>  #[cfg(test)]
>  mod tests {
>      use super::*;
Miguel Ojeda Nov. 14, 2022, 6:28 p.m. UTC | #2 
On Mon, Nov 14, 2022 at 3:39 PM Gary Guo <gary@garyguo.net> wrote:
>
> I wrote this code when `const_panic` was not yet stable. Now we have
> stable const panic this function could be removed.

Indeed, we also took advantage of it in `static_assert!` when it got
stabilized but not here. I will update it.

Cheers,
Miguel
diff mbox series

Patch

diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
index 3ed685cb5a3c..3fb73b888dce 100644
--- a/rust/kernel/str.rs
+++ b/rust/kernel/str.rs
@@ -128,6 +128,18 @@  impl CStr {
         Ok(unsafe { Self::from_bytes_with_nul_unchecked(bytes) })
     }
 
+    /// Creates a [`CStr`] from a `[u8]`, panic if input is not valid.
+    ///
+    /// This function is only meant to be used by `c_str!` macro, so
+    /// crates using `c_str!` macro don't have to enable `const_panic` feature.
+    #[doc(hidden)]
+    pub const fn from_bytes_with_nul_unwrap(bytes: &[u8]) -> &Self {
+        match Self::from_bytes_with_nul(bytes) {
+            Ok(v) => v,
+            Err(_) => panic!("string contains interior NUL"),
+        }
+    }
+
     /// Creates a [`CStr`] from a `[u8]` without performing any additional
     /// checks.
     ///
@@ -321,6 +333,26 @@  where
     }
 }
 
+/// Creates a new [`CStr`] from a string literal.
+///
+/// The string literal should not contain any `NUL` bytes.
+///
+/// # Examples
+///
+/// ```
+/// # use kernel::c_str;
+/// # use kernel::str::CStr;
+/// const MY_CSTR: &CStr = c_str!("My awesome CStr!");
+/// ```
+#[macro_export]
+macro_rules! c_str {
+    ($str:expr) => {{
+        const S: &str = concat!($str, "\0");
+        const C: &$crate::str::CStr = $crate::str::CStr::from_bytes_with_nul_unwrap(S.as_bytes());
+        C
+    }};
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;