The current implementation of tests in str.rs use `format!` to format
strings for comparison, which, internally, creates a new `String`.

In order to prepare for getting rid of Rust's alloc crate, we have to
cut this dependency. Instead, implement `format!` for `CString`.

Note that for userspace tests, `Kmalloc`, which is backing `CString`'s
memory, is just a type alias to `Cmalloc`.

Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/str.rs | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
index 209ad1bb1a49..726329530338 100644
--- a/rust/kernel/str.rs
+++ b/rust/kernel/str.rs
@@ -523,7 +523,28 @@ macro_rules! c_str {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use alloc::format;
+
+    struct String(CString);
+
+    impl String {
+        fn from_fmt(args: fmt::Arguments<'_>) -> Self {
+            String(CString::try_from_fmt(args).unwrap())
+        }
+    }
+
+    impl Deref for String {
+        type Target = str;
+
+        fn deref(&self) -> &str {
+            self.0.to_str().unwrap()
+        }
+    }
+
+    macro_rules! format {
+        ($($f:tt)*) => ({
+            &*String::from_fmt(kernel::fmt!($($f)*))
+        })
+    }
 
     const ALL_ASCII_CHARS: &'static str =
         "\\x01\\x02\\x03\\x04\\x05\\x06\\x07\\x08\\x09\\x0a\\x0b\\x0c\\x0d\\x0e\\x0f\
-- 
2.46.0

On Thu, 12 Sep 2024 00:52:59 +0200
Danilo Krummrich <dakr@kernel.org> wrote:

> The current implementation of tests in str.rs use `format!` to format
> strings for comparison, which, internally, creates a new `String`.
> 
> In order to prepare for getting rid of Rust's alloc crate, we have to
> cut this dependency. Instead, implement `format!` for `CString`.
> 
> Note that for userspace tests, `Kmalloc`, which is backing `CString`'s
> memory, is just a type alias to `Cmalloc`.
> 
> Reviewed-by: Alice Ryhl <aliceryhl@google.com>
> Reviewed-by: Benno Lossin <benno.lossin@proton.me>
> Signed-off-by: Danilo Krummrich <dakr@kernel.org>

Reviewed-by: Gary Guo <gary@garyguo.net>

> ---
>  rust/kernel/str.rs | 23 ++++++++++++++++++++++-
>  1 file changed, 22 insertions(+), 1 deletion(-)
> 
> diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
> index 209ad1bb1a49..726329530338 100644
> --- a/rust/kernel/str.rs
> +++ b/rust/kernel/str.rs
> @@ -523,7 +523,28 @@ macro_rules! c_str {
>  #[cfg(test)]
>  mod tests {
>      use super::*;
> -    use alloc::format;
> +
> +    struct String(CString);
> +
> +    impl String {
> +        fn from_fmt(args: fmt::Arguments<'_>) -> Self {
> +            String(CString::try_from_fmt(args).unwrap())
> +        }
> +    }
> +
> +    impl Deref for String {
> +        type Target = str;
> +
> +        fn deref(&self) -> &str {
> +            self.0.to_str().unwrap()
> +        }
> +    }
> +
> +    macro_rules! format {
> +        ($($f:tt)*) => ({
> +            &*String::from_fmt(kernel::fmt!($($f)*))
> +        })
> +    }
>  
>      const ALL_ASCII_CHARS: &'static str =
>          "\\x01\\x02\\x03\\x04\\x05\\x06\\x07\\x08\\x09\\x0a\\x0b\\x0c\\x0d\\x0e\\x0f\