Add clippy linting to all packages

.github/workflows/clippy.yml

@@ -0,0 +1,45 @@
+name: clippy
+on:
+  merge_group:
+  pull_request:
+
+permissions:
+  contents: read
+
+jobs:
+  check_clippy_configs:
+    runs-on: ubuntu-latest
+    name: check clippy configs
+    steps:
+      - name: checkout
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+      - name: install rustup
+        run: |
+          curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs > rustup-init.sh
+          sh rustup-init.sh -y --default-toolchain none
+          rustup target add x86_64-unknown-linux-gnu
+      - name: Check clippy configs all match
+        run: cargo run --manifest-path ci/Cargo.toml -- clippy-config-check
+
+
+  run_clippy:
+    runs-on: ubuntu-latest
+    name: clippy ${{ matrix.package }}
+    strategy:
+      fail-fast: false
+      matrix:
+        package:
+          - . # rustfmt
+          - check_diff
+          - ci
+          - config_proc_macro
+    steps:
+      - name: checkout
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+      - name: install rustup
+        run: |
+          curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs > rustup-init.sh
+          sh rustup-init.sh -y --default-toolchain none
+      - name: clippy
+        run: cargo clippy --manifest-path ${{ matrix.package }}/Cargo.toml
+

Cargo.toml

@@ -69,3 +69,17 @@ insta = { version = "1.48.0", features = ["filters"] }
 [package.metadata.rust-analyzer]
 # This package uses #[feature(rustc_private)]
 rustc_private = true
+
+[lints.clippy]
+# allow all rules with a low priority ..
+all = { level = "allow", priority = -1 }
+# so we can pick out an exact subset of rules to deny
+correctness = "deny"
+char_lit_as_u8 = "deny"
+four_forward_slashes = "deny"
+non_minimal_cfg = "deny"
+print_literal = "deny"
+same_item_push = "deny"
+single_char_add_str = "deny"
+to_string_in_format_args = "deny"
+unconditional_recursion = "deny"

Contributing.md

@@ -17,6 +17,26 @@ assistance when participating in `rust-lang/rustfmt`.
 
 [LLM usage policy]: https://forge.rust-lang.org/policies/llm-usage.html
 
+## Linting
+
+This project supports linting via
+[`clippy`](https://doc.rust-lang.org/stable/clippy/index.html). You can either
+run it directly, or use an integration through your editor.
+
+```
+# lint rustfmt-nightly (the package at the root of this repo)
+cargo clippy
+```
+
+To Lint a package outside of the root one you will need to do one of:
+
+```
+# pass the manifest path
+cargo clippy --manifest-path ./config_proc_macro/Config.toml
+# or run the command from within the package
+cd ./config_proc_macro
+cargo clippy
+```
 
 ## Test and file issues
 

ci/Cargo.toml

@@ -5,3 +5,21 @@ edition = "2024"
 publish = false
 
 [workspace]
+
+[dependencies]
+itertools = "0.15.0"
+toml = "1.1.5"
+
+[lints.clippy]
+# allow all rules with a low priority ..
+all = { level = "allow", priority = -1 }
+# so we can pick out an exact subset of rules to deny
+correctness = "deny"
+char_lit_as_u8 = "deny"
+four_forward_slashes = "deny"
+non_minimal_cfg = "deny"
+print_literal = "deny"
+same_item_push = "deny"
+single_char_add_str = "deny"
+to_string_in_format_args = "deny"
+unconditional_recursion = "deny"

ci/src/clippy_config_check.rs

@@ -0,0 +1,40 @@
+use std::fs;
+
+use itertools::Itertools;
+
+const CARGO_TOMLS: &[&'static str] = &[
+    "Cargo.toml",
+    "ci/Cargo.toml",
+    "config_proc_macro/Cargo.toml",
+];
+
+pub(crate) fn runner() -> Result<(), String> {
+    for (first, second) in CARGO_TOMLS.iter().tuple_windows() {
+        let first_table = parse_to_toml(&first)?;
+        let second_table = parse_to_toml(&second)?;
+        assert_eq!(
+            get_lints(first, &first_table)?,
+            get_lints(second, &second_table)?,
+            "Clippy configs do not match between {} and {}",
+            first,
+            second,
+        );
+    }
+    Ok(())
+}
+
+fn parse_to_toml(path: &str) -> Result<toml::Table, String> {
+    let toml_str = fs::read_to_string(path).map_err(|e| format!("reading {}: {}", path, e))?;
+    toml_str
+        .parse::<toml::Table>()
+        .map_err(|e| format!("parsing {} as TOML: {}", path, e))
+}
+
+fn get_lints<'a>(path: &str, toml: &'a toml::Table) -> Result<&'a toml::Value, String> {
+    toml.get("lints")
+        .ok_or(format!("{} is missing key {}", path, "lints"))
+        .and_then(|t| {
+            t.get("clippy")
+                .ok_or(format!("{} is missing key {}", path, "lints.clippy"))
+        })
+}

ci/src/main.rs

@@ -1,4 +1,5 @@
 mod build_and_test;
+mod clippy_config_check;
 mod common;
 mod integration;
 
@@ -7,11 +8,14 @@ fn main() {
     if let Err(error) = match args.next().as_deref() {
         Some("integration") => integration::runner(&mut args),
         Some("build-and-test") => build_and_test::runner(),
+        Some("clippy-config-check") => clippy_config_check::runner(),
         Some(arg) => Err(format!(
-            "Expected `integration` or `build-and-test` as first argument, found {arg:?}"
+            "Expected `integration`, `build-and-test`, or `clippy-config-check` \
+                as first argument, found {arg:?}"
         )),
         None => Err(
-            "Expected `integration` or `build-and-test` as first argument, found nothing"
+            "Expected `integration`, `build-and-test`, or `clippy-config-check` \
+                as first argument, found nothing"
                 .to_string(),
         ),
     } {

config_proc_macro/Cargo.toml

@@ -21,3 +21,17 @@ serde = { version = "1.0.160", features = ["derive"] }
 [features]
 default = []
 debug-with-rustfmt = []
+
+[lints.clippy]
+# allow all rules with a low priority ..
+all = { level = "allow", priority = -1 }
+# so we can pick out an exact subset of rules to deny
+correctness = "deny"
+char_lit_as_u8 = "deny"
+four_forward_slashes = "deny"
+non_minimal_cfg = "deny"
+print_literal = "deny"
+same_item_push = "deny"
+single_char_add_str = "deny"
+to_string_in_format_args = "deny"
+unconditional_recursion = "deny"