Auto merge of #10751 - blyxyas:explain_with_config, r=xFrednet

Add configuration options to `--explain`

This PR rearranges some modules, taking `metadata_collector` out of `internal_lints` and making public just the necessary functions for `explain()` to use.

The output looks something like this:
```sh
$ cargo run --bin cargo-clippy --manifest-path ../rust-clippy/Cargo.toml -- --explain cognitive_complexity
### What it does
Checks for methods with high cognitive complexity.

### Why is this bad?
Methods of high cognitive complexity tend to be hard to
both read and maintain. Also LLVM will tend to optimize small methods better.

### Known problems
Sometimes it's hard to find a way to reduce the
complexity.

### Example
You'll see it when you get the warning.

========================================
Configuration for clippy::cognitive_complexity:
- cognitive-complexity-threshold: The maximum cognitive complexity a function can have (default: 25)
```

Fixes #9990
r? `@xFrednet`

---

changelog: Docs: `cargo clippy --explain LINT` now shows possible configuration options for the explained lint
[#10751](#10751)
<!-- changelog_checked -->

Author: bors

Diff for: clippy_lints/src/lib.rs

@@ -332,8 +332,11 @@ mod zero_div_zero;
 mod zero_sized_map_values;
 // end lints modules, do not remove this comment, it’s used in `update_lints`
 
-use crate::utils::conf::{format_error, TryConf};
 pub use crate::utils::conf::{lookup_conf_file, Conf};
+use crate::utils::{
+    conf::{format_error, metadata::get_configuration_metadata, TryConf},
+    FindAll,
+};
 
 /// Register all pre expansion lints
 ///
@@ -389,7 +392,7 @@ pub fn read_conf(sess: &Session, path: &io::Result<(Option<PathBuf>, Vec<String>
     conf
 }
 
-#[derive(Default)]
+#[derive(Default)] //~ ERROR no such field
 struct RegistrationGroups {
     all: Vec<LintId>,
     cargo: Vec<LintId>,
@@ -472,7 +475,22 @@ pub(crate) struct LintInfo {
 pub fn explain(name: &str) {
     let target = format!("clippy::{}", name.to_ascii_uppercase());
     match declared_lints::LINTS.iter().find(|info| info.lint.name == target) {
-        Some(info) => print!("{}", info.explanation),
+        Some(info) => {
+            println!("{}", info.explanation);
+            // Check if the lint has configuration
+            let mdconf = get_configuration_metadata();
+            if let Some(config_vec_positions) = mdconf
+                .iter()
+                .find_all(|cconf| cconf.lints.contains(&info.lint.name_lower()[8..].to_owned()))
+            {
+                // If it has, print it
+                println!("### Configuration for {}:\n", info.lint.name_lower());
+                for position in config_vec_positions {
+                    let conf = &mdconf[position];
+                    println!("  - {}: {} (default: {})", conf.name, conf.doc, conf.default);
+                }
+            }
+        },
         None => println!("unknown lint: {name}"),
     }
 }

Diff for: clippy_lints/src/utils/conf.rs

@@ -174,16 +174,15 @@ macro_rules! define_Conf {
             }
         }
 
-        #[cfg(feature = "internal")]
         pub mod metadata {
-            use crate::utils::internal_lints::metadata_collector::ClippyConfiguration;
+            use crate::utils::ClippyConfiguration;
 
             macro_rules! wrap_option {
                 () => (None);
                 ($x:literal) => (Some($x));
             }
 
-            pub(crate) fn get_configuration_metadata() -> Vec<ClippyConfiguration> {
+            pub fn get_configuration_metadata() -> Vec<ClippyConfiguration> {
                 vec![
                     $(
                         {

Diff for: clippy_lints/src/utils/internal_lints/metadata_collector.rs

@@ -8,7 +8,11 @@
 //! a simple mistake)
 
 use crate::renamed_lints::RENAMED_LINTS;
-use crate::utils::internal_lints::lint_without_lint_pass::{extract_clippy_version_value, is_lint_ref_type};
+use crate::utils::{
+    collect_configs,
+    internal_lints::lint_without_lint_pass::{extract_clippy_version_value, is_lint_ref_type},
+    ClippyConfiguration,
+};
 
 use clippy_utils::diagnostics::span_lint;
 use clippy_utils::ty::{match_type, walk_ptrs_ty_depth};
@@ -520,111 +524,6 @@ impl Serialize for ApplicabilityInfo {
     }
 }
 
-// ==================================================================
-// Configuration
-// ==================================================================
-#[derive(Debug, Clone, Default)]
-pub struct ClippyConfiguration {
-    name: String,
-    config_type: &'static str,
-    default: String,
-    lints: Vec<String>,
-    doc: String,
-    #[allow(dead_code)]
-    deprecation_reason: Option<&'static str>,
-}
-
-impl ClippyConfiguration {
-    pub fn new(
-        name: &'static str,
-        config_type: &'static str,
-        default: String,
-        doc_comment: &'static str,
-        deprecation_reason: Option<&'static str>,
-    ) -> Self {
-        let (lints, doc) = parse_config_field_doc(doc_comment)
-            .unwrap_or_else(|| (vec![], "[ERROR] MALFORMED DOC COMMENT".to_string()));
-
-        Self {
-            name: to_kebab(name),
-            lints,
-            doc,
-            config_type,
-            default,
-            deprecation_reason,
-        }
-    }
-
-    fn to_markdown_paragraph(&self) -> String {
-        format!(
-            "### {}\n{}\n\n**Default Value:** `{}` (`{}`)\n\n{}\n\n",
-            self.name,
-            self.doc
-                .lines()
-                .map(|line| line.strip_prefix("    ").unwrap_or(line))
-                .join("\n"),
-            self.default,
-            self.config_type,
-            self.lints
-                .iter()
-                .map(|name| name.to_string().split_whitespace().next().unwrap().to_string())
-                .map(|name| format!("* [{name}](https://rust-lang.github.io/rust-clippy/master/index.html#{name})"))
-                .join("\n"),
-        )
-    }
-
-    fn to_markdown_table_entry(&self) -> String {
-        format!("| [{}](#{}) | `{}` |", self.name, self.name, self.default)
-    }
-}
-
-fn collect_configs() -> Vec<ClippyConfiguration> {
-    crate::utils::conf::metadata::get_configuration_metadata()
-}
-
-/// This parses the field documentation of the config struct.
-///
-/// ```rust, ignore
-/// parse_config_field_doc(cx, "Lint: LINT_NAME_1, LINT_NAME_2. Papa penguin, papa penguin")
-/// ```
-///
-/// Would yield:
-/// ```rust, ignore
-/// Some(["lint_name_1", "lint_name_2"], "Papa penguin, papa penguin")
-/// ```
-fn parse_config_field_doc(doc_comment: &str) -> Option<(Vec<String>, String)> {
-    const DOC_START: &str = " Lint: ";
-    if_chain! {
-        if doc_comment.starts_with(DOC_START);
-        if let Some(split_pos) = doc_comment.find('.');
-        then {
-            let mut doc_comment = doc_comment.to_string();
-            let mut documentation = doc_comment.split_off(split_pos);
-
-            // Extract lints
-            doc_comment.make_ascii_lowercase();
-            let lints: Vec<String> = doc_comment
-                .split_off(DOC_START.len())
-                .split(", ")
-                .map(str::to_string)
-                .collect();
-
-            // Format documentation correctly
-            // split off leading `.` from lint name list and indent for correct formatting
-            documentation = documentation.trim_start_matches('.').trim().replace("\n ", "\n    ");
-
-            Some((lints, documentation))
-        } else {
-            None
-        }
-    }
-}
-
-/// Transforms a given `snake_case_string` to a tasty `kebab-case-string`
-fn to_kebab(config_name: &str) -> String {
-    config_name.replace('_', "-")
-}
-
 impl fmt::Display for ClippyConfiguration {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> fmt::Result {
         writeln!(

Diff for: clippy_lints/src/utils/mod.rs

@@ -4,3 +4,143 @@ pub mod dump_hir;
 pub mod format_args_collector;
 #[cfg(feature = "internal")]
 pub mod internal_lints;
+#[cfg(feature = "internal")]
+use itertools::Itertools;
+
+/// Transforms a given `snake_case_string` to a tasty `kebab-case-string`
+fn to_kebab(config_name: &str) -> String {
+    config_name.replace('_', "-")
+}
+
+// ==================================================================
+// Configuration
+// ==================================================================
+#[derive(Debug, Clone, Default)] //~ ERROR no such field
+pub struct ClippyConfiguration {
+    pub name: String,
+    #[allow(dead_code)]
+    config_type: &'static str,
+    pub default: String,
+    pub lints: Vec<String>,
+    pub doc: String,
+    #[allow(dead_code)]
+    deprecation_reason: Option<&'static str>,
+}
+
+impl ClippyConfiguration {
+    pub fn new(
+        name: &'static str,
+        config_type: &'static str,
+        default: String,
+        doc_comment: &'static str,
+        deprecation_reason: Option<&'static str>,
+    ) -> Self {
+        let (lints, doc) = parse_config_field_doc(doc_comment)
+            .unwrap_or_else(|| (vec![], "[ERROR] MALFORMED DOC COMMENT".to_string()));
+
+        Self {
+            name: to_kebab(name),
+            lints,
+            doc,
+            config_type,
+            default,
+            deprecation_reason,
+        }
+    }
+
+    #[cfg(feature = "internal")]
+    fn to_markdown_paragraph(&self) -> String {
+        format!(
+            "### {}\n{}\n\n**Default Value:** `{}` (`{}`)\n\n{}\n\n",
+            self.name,
+            self.doc
+                .lines()
+                .map(|line| line.strip_prefix("    ").unwrap_or(line))
+                .join("\n"),
+            self.default,
+            self.config_type,
+            self.lints
+                .iter()
+                .map(|name| name.to_string().split_whitespace().next().unwrap().to_string())
+                .map(|name| format!("* [{name}](https://rust-lang.github.io/rust-clippy/master/index.html#{name})"))
+                .join("\n"),
+        )
+    }
+
+    #[cfg(feature = "internal")]
+    fn to_markdown_table_entry(&self) -> String {
+        format!("| [{}](#{}) | `{}` |", self.name, self.name, self.default)
+    }
+}
+
+#[cfg(feature = "internal")]
+fn collect_configs() -> Vec<ClippyConfiguration> {
+    crate::utils::conf::metadata::get_configuration_metadata()
+}
+
+/// This parses the field documentation of the config struct.
+///
+/// ```rust, ignore
+/// parse_config_field_doc(cx, "Lint: LINT_NAME_1, LINT_NAME_2. Papa penguin, papa penguin")
+/// ```
+///
+/// Would yield:
+/// ```rust, ignore
+/// Some(["lint_name_1", "lint_name_2"], "Papa penguin, papa penguin")
+/// ```
+fn parse_config_field_doc(doc_comment: &str) -> Option<(Vec<String>, String)> {
+    const DOC_START: &str = " Lint: ";
+    if_chain! {
+        if doc_comment.starts_with(DOC_START);
+        if let Some(split_pos) = doc_comment.find('.');
+        then {
+            let mut doc_comment = doc_comment.to_string();
+            let mut documentation = doc_comment.split_off(split_pos);
+
+            // Extract lints
+            doc_comment.make_ascii_lowercase();
+            let lints: Vec<String> = doc_comment
+                .split_off(DOC_START.len())
+                .split(", ")
+                .map(str::to_string)
+                .collect();
+
+            // Format documentation correctly
+            // split off leading `.` from lint name list and indent for correct formatting
+            documentation = documentation.trim_start_matches('.').trim().replace("\n ", "\n    ");
+
+            Some((lints, documentation))
+        } else {
+            None
+        }
+    }
+}
+
+// Shamelessly stolen from find_all (https://github.com/nectariner/find_all)
+pub trait FindAll: Iterator + Sized {
+    fn find_all<P>(&mut self, predicate: P) -> Option<Vec<usize>>
+    where
+        P: FnMut(&Self::Item) -> bool;
+}
+
+impl<I> FindAll for I
+where
+    I: Iterator,
+{
+    fn find_all<P>(&mut self, mut predicate: P) -> Option<Vec<usize>>
+    where
+        P: FnMut(&Self::Item) -> bool,
+    {
+        let mut occurences = Vec::<usize>::default();
+        for (index, element) in self.enumerate() {
+            if predicate(&element) {
+                occurences.push(index);
+            }
+        }
+
+        match occurences.len() {
+            0 => None,
+            _ => Some(occurences),
+        }
+    }
+}