Auto merge of rust-lang#8843 - Serial-ATA:collect-renamed, r=xFrednet

Collect renamed lints

changelog: Display past names of renamed lints on Clippy's lint list

cc rust-lang#7172

r? `@xFrednet`

clippy_lints/src/utils/internal_lints/metadata_collector.rs

@@ -7,6 +7,7 @@
 //! during any comparison or mapping. (Please take care of this, it's not fun to spend time on such
 //! a simple mistake)
 
+use crate::renamed_lints::RENAMED_LINTS;
 use crate::utils::internal_lints::{extract_clippy_version_value, is_lint_ref_type};
 
 use clippy_utils::diagnostics::span_lint;
@@ -26,6 +27,7 @@ use rustc_span::{sym, Loc, Span, Symbol};
 use serde::{ser::SerializeStruct, Serialize, Serializer};
 use std::collections::BinaryHeap;
 use std::fmt;
+use std::fmt::Write as _;
 use std::fs::{self, OpenOptions};
 use std::io::prelude::*;
 use std::path::Path;
@@ -85,6 +87,21 @@ macro_rules! CONFIGURATION_VALUE_TEMPLATE {
     };
 }
 
+macro_rules! RENAMES_SECTION_TEMPLATE {
+    () => {
+        r#"
+### Past names
+
+{names}
+"#
+    };
+}
+macro_rules! RENAME_VALUE_TEMPLATE {
+    () => {
+        "* `{name}`\n"
+    };
+}
+
 const LINT_EMISSION_FUNCTIONS: [&[&str]; 8] = [
     &["clippy_utils", "diagnostics", "span_lint"],
     &["clippy_utils", "diagnostics", "span_lint_and_help"],
@@ -198,9 +215,10 @@ impl Drop for MetadataCollector {
 
         // Mapping the final data
         let mut lints = std::mem::take(&mut self.lints).into_sorted_vec();
-        lints
-            .iter_mut()
-            .for_each(|x| x.applicability = Some(applicability_info.remove(&x.id).unwrap_or_default()));
+        collect_renames(&mut lints);
+        for x in &mut lints {
+            x.applicability = Some(applicability_info.remove(&x.id).unwrap_or_default());
+        }
 
         // Outputting
         if Path::new(OUTPUT_FILE).exists() {
@@ -642,6 +660,37 @@ fn is_deprecated_lint(cx: &LateContext<'_>, ty: &hir::Ty<'_>) -> bool {
     false
 }
 
+fn collect_renames(lints: &mut Vec<LintMetadata>) {
+    for lint in lints {
+        let mut collected = String::new();
+        let mut names = vec![lint.id.clone()];
+
+        loop {
+            if let Some(lint_name) = names.pop() {
+                for (k, v) in RENAMED_LINTS {
+                    if_chain! {
+                        if let Some(name) = v.strip_prefix(CLIPPY_LINT_GROUP_PREFIX);
+                        if name == lint_name;
+                        if let Some(past_name) = k.strip_prefix(CLIPPY_LINT_GROUP_PREFIX);
+                        then {
+                            write!(collected, RENAME_VALUE_TEMPLATE!(), name = past_name).unwrap();
+                            names.push(past_name.to_string());
+                        }
+                    }
+                }
+
+                continue;
+            }
+
+            break;
+        }
+
+        if !collected.is_empty() {
+            write!(&mut lint.docs, RENAMES_SECTION_TEMPLATE!(), names = collected).unwrap();
+        }
+    }
+}
+
 // ==================================================================
 // Lint emission
 // ==================================================================