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comprehensive-rust/src/chromium/interoperability-with-cpp/using-cxx-in-chromium.md

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Add Chromium section (#1479) This is a contribution of a Chromium section for Comprehensive Rust. --------- Co-authored-by: Nicole L <dlegare.1001@gmail.com> Co-authored-by: Martin Geisler <martin@geisler.net>
2023-11-27 18:21:19 +00:00
## Using cxx in Chromium
In Chromium, we define an independent `#[cxx::bridge] mod` for each leaf-node
where we want to use Rust. You'd typically have one for each
`rust_static_library`. Just add
```gn
cxx_bindings = [ "my_rust_file.rs" ]
# list of files containing #[cxx::bridge], not all source files
allow_unsafe = true
```
to your existing `rust_static_library` target alongside `crate_root` and
`sources`.
C++ headers will be generated at a sensible location, so you can just
```cpp
#include "ui/base/my_rust_file.rs.h"
```
Format all Markdown files with `dprint` (#1157) This is the result of running `dprint fmt` after removing `src/` from the list of excluded directories. This also reformats the Rust code: we might want to tweak this a bit in the future since some of the changes removes the hand-formatting. Of course, this formatting can be seen as a mis-feature, so maybe this is good overall. Thanks to mdbook-i18n-helpers 0.2, the POT file is nearly unchanged after this, meaning that all existing translations remain valid! A few messages were changed because of stray whitespace characters: msgid "" "Slices always borrow from another object. In this example, `a` has to remain " -"'alive' (in scope) for at least as long as our slice. " +"'alive' (in scope) for at least as long as our slice." msgstr "" The formatting is enforced in CI and we will have to see how annoying this is in practice for the many contributors. If it becomes annoying, we should look into fixing dprint/check#11 so that `dprint` can annotate the lines that need fixing directly, then I think we can consider more strict formatting checks. I added more customization to `rustfmt.toml`. This is to better emulate the dense style used in the course: - `max_width = 85` allows lines to take up the full width available in our code blocks (when taking margins and the line numbers into account). - `wrap_comments = true` ensures that we don't show very long comments in the code examples. I edited some comments to shorten them and avoid unnecessary line breaks — please trim other unnecessarily long comments when you see them! Remember we're writing code for slides :smile: - `use_small_heuristics = "Max"` allows for things like struct literals and if-statements to take up the full line width configured above. The formatting settings apply to all our Rust code right now — I think we could improve this with https://github.com/dprint/dprint/issues/711 which lets us add per-directory `dprint` configuration files. However, the `inherit: true` setting is not yet implemented (as far as I can tell), so a nested configuration file will have to copy most or all of the top-level file.
2023-12-31 00:15:07 +01:00
You will find some utility functions in `//base` to convert to/from Chromium C++
types to CXX Rust types --- for example [`SpanToRustSlice`][0].
Add Chromium section (#1479) This is a contribution of a Chromium section for Comprehensive Rust. --------- Co-authored-by: Nicole L <dlegare.1001@gmail.com> Co-authored-by: Martin Geisler <martin@geisler.net>
2023-11-27 18:21:19 +00:00
<details>
Replace hyphens (`-`) with em-dashes (`—`) (#1500) The new Chromium class likes — like me! — to use dashes in the writing! However, I believe it should use an em-dash instead of the hyphen. Luckily this is easy: we have enabled “typographic quotes” in `mdbook`, which also handles the conversion of `---` to `—` in the generated HTML. So I normalized the single existing em-dash to a triple-dash to make it more consistent (and hopefully make it easier for translators to consistently enter these characters).
2023-11-28 19:41:09 +01:00
Students may ask --- why do we still need `allow_unsafe = true`?
Add Chromium section (#1479) This is a contribution of a Chromium section for Comprehensive Rust. --------- Co-authored-by: Nicole L <dlegare.1001@gmail.com> Co-authored-by: Martin Geisler <martin@geisler.net>
2023-11-27 18:21:19 +00:00
The broad answer is that no C/C++ code is "safe" by the normal Rust standards.
Calling back and forth to C/C++ from Rust may do arbitrary things to memory, and
compromise the safety of Rust's own data layouts. Presence of _too many_
Format all Markdown files with `dprint` (#1157) This is the result of running `dprint fmt` after removing `src/` from the list of excluded directories. This also reformats the Rust code: we might want to tweak this a bit in the future since some of the changes removes the hand-formatting. Of course, this formatting can be seen as a mis-feature, so maybe this is good overall. Thanks to mdbook-i18n-helpers 0.2, the POT file is nearly unchanged after this, meaning that all existing translations remain valid! A few messages were changed because of stray whitespace characters: msgid "" "Slices always borrow from another object. In this example, `a` has to remain " -"'alive' (in scope) for at least as long as our slice. " +"'alive' (in scope) for at least as long as our slice." msgstr "" The formatting is enforced in CI and we will have to see how annoying this is in practice for the many contributors. If it becomes annoying, we should look into fixing dprint/check#11 so that `dprint` can annotate the lines that need fixing directly, then I think we can consider more strict formatting checks. I added more customization to `rustfmt.toml`. This is to better emulate the dense style used in the course: - `max_width = 85` allows lines to take up the full width available in our code blocks (when taking margins and the line numbers into account). - `wrap_comments = true` ensures that we don't show very long comments in the code examples. I edited some comments to shorten them and avoid unnecessary line breaks — please trim other unnecessarily long comments when you see them! Remember we're writing code for slides :smile: - `use_small_heuristics = "Max"` allows for things like struct literals and if-statements to take up the full line width configured above. The formatting settings apply to all our Rust code right now — I think we could improve this with https://github.com/dprint/dprint/issues/711 which lets us add per-directory `dprint` configuration files. However, the `inherit: true` setting is not yet implemented (as far as I can tell), so a nested configuration file will have to copy most or all of the top-level file.
2023-12-31 00:15:07 +01:00
`unsafe` keywords in C/C++ interop can harm the signal-to-noise ratio of such a
keyword, and is [controversial][1], but strictly, bringing any foreign code into
a Rust binary can cause unexpected behavior from Rust's perspective.
Add Chromium section (#1479) This is a contribution of a Chromium section for Comprehensive Rust. --------- Co-authored-by: Nicole L <dlegare.1001@gmail.com> Co-authored-by: Martin Geisler <martin@geisler.net>
2023-11-27 18:21:19 +00:00
Format all Markdown files with `dprint` (#1157) This is the result of running `dprint fmt` after removing `src/` from the list of excluded directories. This also reformats the Rust code: we might want to tweak this a bit in the future since some of the changes removes the hand-formatting. Of course, this formatting can be seen as a mis-feature, so maybe this is good overall. Thanks to mdbook-i18n-helpers 0.2, the POT file is nearly unchanged after this, meaning that all existing translations remain valid! A few messages were changed because of stray whitespace characters: msgid "" "Slices always borrow from another object. In this example, `a` has to remain " -"'alive' (in scope) for at least as long as our slice. " +"'alive' (in scope) for at least as long as our slice." msgstr "" The formatting is enforced in CI and we will have to see how annoying this is in practice for the many contributors. If it becomes annoying, we should look into fixing dprint/check#11 so that `dprint` can annotate the lines that need fixing directly, then I think we can consider more strict formatting checks. I added more customization to `rustfmt.toml`. This is to better emulate the dense style used in the course: - `max_width = 85` allows lines to take up the full width available in our code blocks (when taking margins and the line numbers into account). - `wrap_comments = true` ensures that we don't show very long comments in the code examples. I edited some comments to shorten them and avoid unnecessary line breaks — please trim other unnecessarily long comments when you see them! Remember we're writing code for slides :smile: - `use_small_heuristics = "Max"` allows for things like struct literals and if-statements to take up the full line width configured above. The formatting settings apply to all our Rust code right now — I think we could improve this with https://github.com/dprint/dprint/issues/711 which lets us add per-directory `dprint` configuration files. However, the `inherit: true` setting is not yet implemented (as far as I can tell), so a nested configuration file will have to copy most or all of the top-level file.
2023-12-31 00:15:07 +01:00
The narrow answer lies in the diagram at the top of [this page][2] --- behind
the scenes, CXX generates Rust `unsafe` and `extern "C"` functions just like we
did manually in the previous section.
Replace hyphens (`-`) with em-dashes (`—`) (#1500) The new Chromium class likes — like me! — to use dashes in the writing! However, I believe it should use an em-dash instead of the hyphen. Luckily this is easy: we have enabled “typographic quotes” in `mdbook`, which also handles the conversion of `---` to `—` in the generated HTML. So I normalized the single existing em-dash to a triple-dash to make it more consistent (and hopefully make it easier for translators to consistently enter these characters).
2023-11-28 19:41:09 +01:00
Add Chromium section (#1479) This is a contribution of a Chromium section for Comprehensive Rust. --------- Co-authored-by: Nicole L <dlegare.1001@gmail.com> Co-authored-by: Martin Geisler <martin@geisler.net>
2023-11-27 18:21:19 +00:00
</details>
[0]: https://source.chromium.org/chromium/chromium/src/+/main:base/containers/span_rust.h;l=21
Replace hyphens (`-`) with em-dashes (`—`) (#1500) The new Chromium class likes — like me! — to use dashes in the writing! However, I believe it should use an em-dash instead of the hyphen. Luckily this is easy: we have enabled “typographic quotes” in `mdbook`, which also handles the conversion of `---` to `—` in the generated HTML. So I normalized the single existing em-dash to a triple-dash to make it more consistent (and hopefully make it easier for translators to consistently enter these characters).
2023-11-28 19:41:09 +01:00
[1]: https://steveklabnik.com/writing/the-cxx-debate
Format all Markdown files with `dprint` (#1157) This is the result of running `dprint fmt` after removing `src/` from the list of excluded directories. This also reformats the Rust code: we might want to tweak this a bit in the future since some of the changes removes the hand-formatting. Of course, this formatting can be seen as a mis-feature, so maybe this is good overall. Thanks to mdbook-i18n-helpers 0.2, the POT file is nearly unchanged after this, meaning that all existing translations remain valid! A few messages were changed because of stray whitespace characters: msgid "" "Slices always borrow from another object. In this example, `a` has to remain " -"'alive' (in scope) for at least as long as our slice. " +"'alive' (in scope) for at least as long as our slice." msgstr "" The formatting is enforced in CI and we will have to see how annoying this is in practice for the many contributors. If it becomes annoying, we should look into fixing dprint/check#11 so that `dprint` can annotate the lines that need fixing directly, then I think we can consider more strict formatting checks. I added more customization to `rustfmt.toml`. This is to better emulate the dense style used in the course: - `max_width = 85` allows lines to take up the full width available in our code blocks (when taking margins and the line numbers into account). - `wrap_comments = true` ensures that we don't show very long comments in the code examples. I edited some comments to shorten them and avoid unnecessary line breaks — please trim other unnecessarily long comments when you see them! Remember we're writing code for slides :smile: - `use_small_heuristics = "Max"` allows for things like struct literals and if-statements to take up the full line width configured above. The formatting settings apply to all our Rust code right now — I think we could improve this with https://github.com/dprint/dprint/issues/711 which lets us add per-directory `dprint` configuration files. However, the `inherit: true` setting is not yet implemented (as far as I can tell), so a nested configuration file will have to copy most or all of the top-level file.
2023-12-31 00:15:07 +01:00
[2]: ../interoperability-with-cpp.md
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