.gitattributes: set diff driver for Rust source code files

  Git supports a builtin Rust diff driver [1] since v2.23.0 (2019).

It improves the choice of hunk headers in some cases, such as
diffs within methods, since those are indented in Rust within
an `impl` block, and therefore the default diff driver would
pick the outer `impl` block instead (rather than the method
where the changed code is).

For instance, with the default diff driver:

    @@ -455,6 +455,8 @@ impl fmt::Write for RawFormatter {
             // Amount that we can copy. `saturating_sub` ensures we get 0 if `pos` goes past `end`.
             let len_to_copy = core::cmp::min(pos_new, self.end).saturating_sub(self.pos);

    +        test_diff_driver();
    +
             if len_to_copy > 0 {
                 // SAFETY: If `len_to_copy` is non-zero, then we know `pos` has not gone past `end`
                 // yet, so it is valid for write per the type invariants.

With the Rust diff driver:

    @@ -455,6 +455,8 @@ fn write_str(&mut self, s: &str) -> fmt::Result {
             // Amount that we can copy. `saturating_sub` ensures we get 0 if `pos` goes past `end`.
             let len_to_copy = core::cmp::min(pos_new, self.end).saturating_sub(self.pos);

    +        test_diff_driver();
    +
             if len_to_copy > 0 {
                 // SAFETY: If `len_to_copy` is non-zero, then we know `pos` has not gone past `end`
                 // yet, so it is valid for write per the type invariants.

Thus set the `rust` diff driver for `*.rs` source files.

Link: https://git-scm.com/docs/gitattributes#_defining_a_custom_hunk_header [1]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
 .gitattributes | 1 +
 1 file changed, 1 insertion(+)


base-commit: 09a9639e56c01c7a00d6c0ca63f4c7c41abe075d
  

On 4/18/23 20:30, Miguel Ojeda wrote:
> Git supports a builtin Rust diff driver [1] since v2.23.0 (2019).
> 
> [...]

At this stage in the game such an improvement in diffs is required.

Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
  

On Wed, 19 Apr 2023 01:30:48 +0200
Miguel Ojeda <ojeda@kernel.org> wrote:

> Git supports a builtin Rust diff driver [1] since v2.23.0 (2019).
> 
> It improves the choice of hunk headers in some cases, such as
> diffs within methods, since those are indented in Rust within
> an `impl` block, and therefore the default diff driver would
> pick the outer `impl` block instead (rather than the method
> where the changed code is).
> 
> For instance, with the default diff driver:
> 
>     @@ -455,6 +455,8 @@ impl fmt::Write for RawFormatter {
>              // Amount that we can copy. `saturating_sub` ensures we get 0 if `pos` goes past `end`.
>              let len_to_copy = core::cmp::min(pos_new, self.end).saturating_sub(self.pos);
> 
>     +        test_diff_driver();
>     +
>              if len_to_copy > 0 {
>                  // SAFETY: If `len_to_copy` is non-zero, then we know `pos` has not gone past `end`
>                  // yet, so it is valid for write per the type invariants.
> 
> With the Rust diff driver:
> 
>     @@ -455,6 +455,8 @@ fn write_str(&mut self, s: &str) -> fmt::Result {
>              // Amount that we can copy. `saturating_sub` ensures we get 0 if `pos` goes past `end`.
>              let len_to_copy = core::cmp::min(pos_new, self.end).saturating_sub(self.pos);
> 
>     +        test_diff_driver();
>     +
>              if len_to_copy > 0 {
>                  // SAFETY: If `len_to_copy` is non-zero, then we know `pos` has not gone past `end`
>                  // yet, so it is valid for write per the type invariants.
> 
> Thus set the `rust` diff driver for `*.rs` source files.
> 
> Link: https://git-scm.com/docs/gitattributes#_defining_a_custom_hunk_header [1]
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

This is also done in rustc repo:
https://github.com/rust-lang/rust/blob/master/.gitattributes

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

> ---
>  .gitattributes | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/.gitattributes b/.gitattributes
> index c9ba5bfc4036..2325c529e185 100644
> --- a/.gitattributes
> +++ b/.gitattributes
> @@ -2,3 +2,4 @@
>  *.[ch] diff=cpp
>  *.dts diff=dts
>  *.dts[io] diff=dts
> +*.rs diff=rust
> 
> base-commit: 09a9639e56c01c7a00d6c0ca63f4c7c41abe075d
  

On 19.04.23 01:30, Miguel Ojeda wrote:
> Git supports a builtin Rust diff driver [1] since v2.23.0 (2019).
> 
> It improves the choice of hunk headers in some cases, such as
> diffs within methods, since those are indented in Rust within
> an `impl` block, and therefore the default diff driver would
> pick the outer `impl` block instead (rather than the method
> where the changed code is).
> 
> For instance, with the default diff driver:
> 
>      @@ -455,6 +455,8 @@ impl fmt::Write for RawFormatter {
>               // Amount that we can copy. `saturating_sub` ensures we get 0 if `pos` goes past `end`.
>               let len_to_copy = core::cmp::min(pos_new, self.end).saturating_sub(self.pos);
> 
>      +        test_diff_driver();
>      +
>               if len_to_copy > 0 {
>                   // SAFETY: If `len_to_copy` is non-zero, then we know `pos` has not gone past `end`
>                   // yet, so it is valid for write per the type invariants.
> 
> With the Rust diff driver:
> 
>      @@ -455,6 +455,8 @@ fn write_str(&mut self, s: &str) -> fmt::Result {
>               // Amount that we can copy. `saturating_sub` ensures we get 0 if `pos` goes past `end`.
>               let len_to_copy = core::cmp::min(pos_new, self.end).saturating_sub(self.pos);
> 
>      +        test_diff_driver();
>      +
>               if len_to_copy > 0 {
>                   // SAFETY: If `len_to_copy` is non-zero, then we know `pos` has not gone past `end`
>                   // yet, so it is valid for write per the type invariants.
> 
> Thus set the `rust` diff driver for `*.rs` source files.
> 
> Link: https://git-scm.com/docs/gitattributes#_defining_a_custom_hunk_header [1]
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Reviewed-by: Benno Lossin <benno.lossin@proton.me>

> ---
>   .gitattributes | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/.gitattributes b/.gitattributes
> index c9ba5bfc4036..2325c529e185 100644
> --- a/.gitattributes
> +++ b/.gitattributes
> @@ -2,3 +2,4 @@
>   *.[ch] diff=cpp
>   *.dts diff=dts
>   *.dts[io] diff=dts
> +*.rs diff=rust
> 
> base-commit: 09a9639e56c01c7a00d6c0ca63f4c7c41abe075d
> --
> 2.40.0
>
  

On Wed, Apr 19, 2023 at 1:31 AM Miguel Ojeda <ojeda@kernel.org> wrote:
>
> Thus set the `rust` diff driver for `*.rs` source files.
>
> Link: https://git-scm.com/docs/gitattributes#_defining_a_custom_hunk_header [1]
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Applied to `rust-next` (with an extra link based on Gary's) -- thanks
everyone for reviewing!

Cheers,
Miguel