Document coding style

.clang-format

@@ -0,0 +1,20 @@
+# Licensed under the Apache-2.0 license
+# SPDX-License-Identifier: Apache-2.0
+
+# Documentation for this configuration is here:
+#   https://releases.llvm.org/6.0.0/tools/clang/docs/ClangFormatStyleOptions.html
+
+BasedOnStyle: Google
+IndentWidth: 4
+AllowShortIfStatementsOnASingleLine: false
+AllowShortLoopsOnASingleLine: false
+DerivePointerAlignment: false
+PointerAlignment: Right
+
+IncludeCategories:
+- # System Headers: #include <*>
+  Regex: '^<.*>$'
+  Priority: 1
+- # All Other Headers
+  Regex: '.*'
+  Priority: 2

docs/src/SUMMARY.md

@@ -26,6 +26,7 @@
 # Developer Guide
 
 * [Architecture](./architecture.md)
+* [Coding Style](./coding-style.md)
 * [Contributing](./contributing.md)
 * [Design](./design/README.md)
   * [Digest Driver for Hubris](./design/driver-hubris-hash.md)

docs/src/coding-style.md

@@ -0,0 +1,39 @@
+# Coding Style
+
+This document describes the coding style used by this project.
+All of the formatters can be invoked by the `pw` utility script in the root of
+the project:
+
+```
+$ ./pw format
+```
+
+## Rust
+
+This project follows the standard [Rust Style
+Guide](https://doc.rust-lang.org/style-guide/) for Rust code.  Formatting is
+done with `rustfmt` using the
+[`rustfmt.toml`](https://github.com/pigweed-project/pigweed/blob/main/rustfmt.toml)
+from the upstream [Pigweed](https://github.com/pigweed-project/pigweed/) repository.
+
+## Python
+
+This project follows [PEP8](https://peps.python.org/pep-0008/) for Python code.
+Formatting is done with the `black` formatter.
+
+## Starlark (bazel build system)
+
+This project follows the standard [bzl style
+guide](https://bazel.build/rules/bzl-style) for Starlark code.
+Formatting is done with the `buildifier` tool.
+
+## C / C++
+
+This project follows the [Google C++ Style Guide] for C and C++ code, with the
+following exceptions:
+- Indent is 4 spaces instead of 2.
+- Function names should use `snake_case` instead of `PascalCase`.
+- In pointer declarations, the asterisk is attached to the variable name (`int
+  *foo`) instead of the type name (`int* foo`).
+
+Formatting is done with `clang-format`.

docs/src/contributing.md

@@ -18,7 +18,7 @@ The code of conduct can be found [here](https://github.com/OpenPRoT/.github/blob
 
 ## Code Style
 
-- Use `cargo xtask fmt` to format code
+- Follow the [coding style](coding-style.md) guide.
 - Run `cargo xtask clippy` to check for lints
 - Ensure all tests pass with `cargo xtask test`