From c7aa411fabb88f0340257d2f31de2226f9433475 Mon Sep 17 00:00:00 2001
From: y21 <30553356+y21@users.noreply.github.com>
Date: Sat, 5 Oct 2024 02:23:59 +0200
Subject: [PATCH] add a book page for lighter, more granular lint groups

---
 Cargo.toml                       |   1 +
 book/src/SUMMARY.md              |   1 +
 book/src/granular_lint_groups.md | 219 +++++++++++++++++++++++++++++++
 tests/lint-groups.rs             | 132 +++++++++++++++++++
 4 files changed, 353 insertions(+)
 create mode 100644 book/src/granular_lint_groups.md
 create mode 100644 tests/lint-groups.rs

diff --git a/Cargo.toml b/Cargo.toml
index ddc27179ef2f..f5bae35a5b22 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -38,6 +38,7 @@ serde_json = "1.0.122"
 toml = "0.7.3"
 walkdir = "2.3"
 filetime = "0.2.9"
+indoc = "1.0"
 itertools = "0.12"
 
 # UI test dependencies
diff --git a/book/src/SUMMARY.md b/book/src/SUMMARY.md
index be13fcbe260f..040eb7db02ed 100644
--- a/book/src/SUMMARY.md
+++ b/book/src/SUMMARY.md
@@ -7,6 +7,7 @@
 - [Configuration](configuration.md)
     - [Lint Configuration](lint_configuration.md)
 - [Clippy's Lints](lints.md)
+- [More granular lint groups](granular_lint_groups.md)
 - [Continuous Integration](continuous_integration/README.md)
     - [GitHub Actions](continuous_integration/github_actions.md)
     - [GitLab CI](continuous_integration/gitlab.md)
diff --git a/book/src/granular_lint_groups.md b/book/src/granular_lint_groups.md
new file mode 100644
index 000000000000..cd645c22b7e2
--- /dev/null
+++ b/book/src/granular_lint_groups.md
@@ -0,0 +1,219 @@
+# More granular lint groups
+
+Clippy groups its lints into [9 primary categories](lints.md),
+two of which are allow-by-default (pedantic and restriction).
+
+One downside with having such few but broad categories for allow-by-default lints
+is that it significantly decreases discoverability, as `restriction` often acts as a blanket category
+for any lint that most users likely would not want enforced on their codebase.
+
+This page should help with that, by defining more granular, unofficial lint groups.
+For example, some people might not be interested in all the style-related `pedantic` lints,
+but *are* interested in the `perf`-related ones, so it can be worth going through some of these.
+
+<!--
+NOTE: Do not edit the contents in between lint-group-start and lint-group-end manually.
+These sections are generated based on the `GROUPS` array defined in tests/lint-groups.rs,
+so consider updating that instead and re-running `cargo bless`.
+The descriptions however are fine to edit.
+-->
+
+## Perf-pedantic
+
+These are `pedantic` lints that look for code patterns that could be expressed in a more efficient way.
+These would be candidates for the `perf` category, however suggestions made by them can also sometimes hurt readability
+and obfuscate the meaning, so occasional `#[allow]`s are expected to be used.
+
+<!-- lint-group-start: perf-pedantic -->
+Lints: `assigning_clones`, `inefficient_to_string`, `naive_bytecount`, `needless_bitwise_bool`, `trivially_copy_pass_by_ref`, `unnecessary_join`, `unnecessary_box_returns`
+
+<details>
+<summary>#![warn] attribute</summary>
+
+```
+#![warn(
+    clippy::assigning_clones,
+    clippy::inefficient_to_string,
+    clippy::naive_bytecount,
+    clippy::needless_bitwise_bool,
+    clippy::trivially_copy_pass_by_ref,
+    clippy::unnecessary_join,
+    clippy::unnecessary_box_returns
+)]
+```
+</details>
+
+<details>
+<summary>Lint table</summary>
+
+```
+[lints.clippy]
+assigning_clones = "warn"
+inefficient_to_string = "warn"
+naive_bytecount = "warn"
+needless_bitwise_bool = "warn"
+trivially_copy_pass_by_ref = "warn"
+unnecessary_join = "warn"
+unnecessary_box_returns = "warn"
+```
+</details>
+<!-- lint-group-end: perf-pedantic -->
+
+
+## Perf-restriction
+
+These are `restriction` lints that can improve the performance of code, but are very specific
+and sometimes *significantly* hurt readability with very little gain in the usual case.
+These should ideally only be applied to specific functions or modules that were profiled
+and where it is very clear that any performance gain matters.
+
+As always (but especially here), you should double-check that applying these actually helps
+and that any performance wins are worth the introduced complexity.
+
+<!-- lint-group-start: perf-restriction -->
+Lints: `format_push_string`, `missing_asserts_for_indexing`
+
+<details>
+<summary>#![warn] attribute</summary>
+
+```
+#![warn(
+    clippy::format_push_string,
+    clippy::missing_asserts_for_indexing
+)]
+```
+</details>
+
+<details>
+<summary>Lint table</summary>
+
+```
+[lints.clippy]
+format_push_string = "warn"
+missing_asserts_for_indexing = "warn"
+```
+</details>
+<!-- lint-group-end: perf-restriction -->
+
+## Perf-nursery
+
+These are `nursery` lints that either were previously in the `perf` category or are intended to be in `perf`
+but have too many false positives.
+Some of them may also be simply wrong in certain situations and end up slower,
+so you should make sure to read the description to learn about possible edge cases.
+
+<!-- lint-group-start: perf-nursery -->
+Lints: `redundant_clone`, `iter_with_drain`, `mutex_integer`, `or_fun_call`, `significant_drop_tightening`, `trivial_regex`, `needless_collect`
+
+<details>
+<summary>#![warn] attribute</summary>
+
+```
+#![warn(
+    clippy::redundant_clone,
+    clippy::iter_with_drain,
+    clippy::mutex_integer,
+    clippy::or_fun_call,
+    clippy::significant_drop_tightening,
+    clippy::trivial_regex,
+    clippy::needless_collect
+)]
+```
+</details>
+
+<details>
+<summary>Lint table</summary>
+
+```
+[lints.clippy]
+redundant_clone = "warn"
+iter_with_drain = "warn"
+mutex_integer = "warn"
+or_fun_call = "warn"
+significant_drop_tightening = "warn"
+trivial_regex = "warn"
+needless_collect = "warn"
+```
+</details>
+<!-- lint-group-end: perf-nursery -->
+
+## Panicking
+
+These are `restriction` lints that look for patterns that can introduce panics.
+
+Usually panics are not something that one should want to avoid and most of the time panicking is perfectly valid
+(hence why these lints are allow-by-default),
+but users may want to forbid any use of panicky functions altogether in specific contexts.
+
+One use case could be to annotate `GlobalAlloc` impls in which unwinding is Undefined Behavior.
+
+<!-- lint-group-start: panicking -->
+Lints: `arithmetic_side_effects`, `expect_used`, `unwrap_used`, `panic`, `unreachable`, `todo`, `unimplemented`, `string_slice`, `indexing_slicing`
+
+<details>
+<summary>#![warn] attribute</summary>
+
+```
+#![warn(
+    clippy::arithmetic_side_effects,
+    clippy::expect_used,
+    clippy::unwrap_used,
+    clippy::panic,
+    clippy::unreachable,
+    clippy::todo,
+    clippy::unimplemented,
+    clippy::string_slice,
+    clippy::indexing_slicing
+)]
+```
+</details>
+
+<details>
+<summary>Lint table</summary>
+
+```
+[lints.clippy]
+arithmetic_side_effects = "warn"
+expect_used = "warn"
+unwrap_used = "warn"
+panic = "warn"
+unreachable = "warn"
+todo = "warn"
+unimplemented = "warn"
+string_slice = "warn"
+indexing_slicing = "warn"
+```
+</details>
+<!-- lint-group-end: panicking -->
+
+## Debugging
+
+These are lints that can be useful to disable in CI, as they might indicate that code needs more work
+or has remaining debugging artifacts.
+
+<!-- lint-group-start: debugging -->
+Lints: `dbg_macro`, `todo`, `unimplemented`
+
+<details>
+<summary>#![warn] attribute</summary>
+
+```
+#![warn(
+    clippy::dbg_macro,
+    clippy::todo,
+    clippy::unimplemented
+)]
+```
+</details>
+
+<details>
+<summary>Lint table</summary>
+
+```
+[lints.clippy]
+dbg_macro = "warn"
+todo = "warn"
+unimplemented = "warn"
+```
+</details>
+<!-- lint-group-end: debugging -->
diff --git a/tests/lint-groups.rs b/tests/lint-groups.rs
new file mode 100644
index 000000000000..69c9cb6605fc
--- /dev/null
+++ b/tests/lint-groups.rs
@@ -0,0 +1,132 @@
+//! This test checks and updates `book/src/granular_lint_groups.md`
+//!
+//! Specifically the parts in between lint-group-start and lint-group-end are not meant to be edited
+//! by hand and are instead generated based on the const `GROUPS` slice.
+#![feature(rustc_private)]
+
+use std::collections::HashSet;
+use std::{env, fs};
+
+use clippy_lints::LintInfo;
+use clippy_lints::declared_lints::LINTS;
+use indoc::formatdoc;
+use itertools::Itertools;
+use regex::{Captures, Regex};
+
+const GROUPS: &[(&str, &[&str])] = &[
+    ("perf-pedantic", &[
+        "assigning_clones",
+        "inefficient_to_string",
+        "naive_bytecount",
+        "needless_bitwise_bool",
+        "trivially_copy_pass_by_ref",
+        "unnecessary_join",
+        "unnecessary_box_returns",
+    ]),
+    ("perf-restriction", &[
+        "format_push_string",
+        "missing_asserts_for_indexing",
+    ]),
+    ("perf-nursery", &[
+        "redundant_clone",
+        "iter_with_drain",
+        "mutex_integer",
+        "or_fun_call",
+        "significant_drop_tightening",
+        "trivial_regex",
+        "needless_collect",
+    ]),
+    ("panicking", &[
+        "arithmetic_side_effects",
+        "expect_used",
+        "unwrap_used",
+        "panic",
+        "unreachable",
+        "todo",
+        "unimplemented",
+        "string_slice",
+        "indexing_slicing",
+    ]),
+    ("debugging", &["dbg_macro", "todo", "unimplemented"]),
+];
+
+#[test]
+fn check_lint_groups() {
+    let file = fs::read_to_string("book/src/granular_lint_groups.md").expect("failed to read granular_lint_groups.md");
+    let all_lint_names: HashSet<_> = LINTS
+        .iter()
+        .map(|LintInfo { lint, .. }| lint.name.strip_prefix("clippy::").unwrap().to_ascii_lowercase())
+        .collect();
+
+    let regex = Regex::new(
+        "(?s)\
+        (?<header><!-- lint-group-start: (?<name_start>[\\w-]+) -->)\
+        (?<lints>.*?)\
+        (?<footer><!-- lint-group-end: (?<name_end>[\\w-]+) -->)\
+        ",
+    )
+    .unwrap();
+
+    let replaced = regex.replace_all(&file, |captures: &Captures<'_>| -> String {
+        let name = &captures["name_start"];
+
+        assert_eq!(
+            name, &captures["name_end"],
+            "lint-group-start and lint-group-end lint names must match"
+        );
+
+        let lints = GROUPS
+            .iter()
+            .find_map(|&(name2, lints)| (name == name2).then_some(lints))
+            .unwrap_or_else(|| panic!("lint group {name} does not exist"));
+
+        for &lint in lints {
+            assert!(
+                all_lint_names.contains(lint),
+                "lint {lint} in group {name} does not exist"
+            );
+        }
+
+        let spoiler = |summary: &str, contents: &str| {
+            formatdoc! {"
+                <details>
+                <summary>{summary}</summary>
+
+                ```
+                {contents}
+                ```
+                </details>
+            "}
+        };
+
+        let lint_list = format!("Lints: {}", lints.iter().map(|lint| format!("`{lint}`")).join(", "));
+        let warn_attr = spoiler(
+            "#![warn] attribute",
+            &format!(
+                "#![warn({})]",
+                lints.iter().map(|lint| format!("\n    clippy::{lint}")).join(",") + "\n"
+            ),
+        );
+        let lint_table = spoiler(
+            "Lint table",
+            &format!(
+                "[lints.clippy]\n{}",
+                &lints.iter().map(|lint| format!(r#"{lint} = "warn""#)).join("\n")
+            ),
+        );
+
+        format!(
+            "{header}\n{lint_list}\n\n{warn_attr}\n{lint_table}{footer}",
+            header = &captures["header"],
+            footer = &captures["footer"]
+        )
+    });
+
+    if replaced != file {
+        if env::var_os("RUSTC_BLESS").is_some_and(|n| n != "0") {
+            fs::write("book/src/granular_lint_groups.md", &*replaced).unwrap();
+        } else {
+            panic!("granular_lint_groups.md file has changed! Run `cargo bless --test lint-groups` to update.");
+        }
+    }
+}