From 566384e7cdffec8257eced9ef1319ced13e943e5 Mon Sep 17 00:00:00 2001
From: ThibsG <thibsg@pm.me>
Date: Sun, 14 Mar 2021 19:35:35 +0100
Subject: [PATCH] Fix FP in `single_component_path_imports` lint

---
 clippy_lints/src/lib.rs                       |  2 +-
 .../src/single_component_path_imports.rs      | 47 ++++++++++++++++++-
 .../ui/single_component_path_imports_self.rs  | 16 +++++++
 3 files changed, 62 insertions(+), 3 deletions(-)
 create mode 100644 tests/ui/single_component_path_imports_self.rs

diff --git a/clippy_lints/src/lib.rs b/clippy_lints/src/lib.rs
index 04e151df8e85..7021d0fdd6a5 100644
--- a/clippy_lints/src/lib.rs
+++ b/clippy_lints/src/lib.rs
@@ -1231,7 +1231,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     store.register_early_pass(|| box as_conversions::AsConversions);
     store.register_late_pass(|| box let_underscore::LetUnderscore);
     store.register_late_pass(|| box atomic_ordering::AtomicOrdering);
-    store.register_early_pass(|| box single_component_path_imports::SingleComponentPathImports);
+    store.register_early_pass(|| box single_component_path_imports::SingleComponentPathImports::default());
     let max_fn_params_bools = conf.max_fn_params_bools;
     let max_struct_bools = conf.max_struct_bools;
     store.register_early_pass(move || box excessive_bools::ExcessiveBools::new(max_struct_bools, max_fn_params_bools));
diff --git a/clippy_lints/src/single_component_path_imports.rs b/clippy_lints/src/single_component_path_imports.rs
index 1fc4ff5c2e61..7facce258ef4 100644
--- a/clippy_lints/src/single_component_path_imports.rs
+++ b/clippy_lints/src/single_component_path_imports.rs
@@ -3,8 +3,9 @@ use if_chain::if_chain;
 use rustc_ast::{Item, ItemKind, UseTreeKind};
 use rustc_errors::Applicability;
 use rustc_lint::{EarlyContext, EarlyLintPass};
-use rustc_session::{declare_lint_pass, declare_tool_lint};
+use rustc_session::{declare_tool_lint, impl_lint_pass};
 use rustc_span::edition::Edition;
+use rustc_span::Symbol;
 
 declare_clippy_lint! {
     /// **What it does:** Checking for imports with single component use path.
@@ -34,10 +35,50 @@ declare_clippy_lint! {
     "imports with single component path are redundant"
 }
 
-declare_lint_pass!(SingleComponentPathImports => [SINGLE_COMPONENT_PATH_IMPORTS]);
+#[derive(Default)]
+pub struct SingleComponentPathImports {
+    /// detect imports reused with `self` keyword,
+    /// such as `self::crypto_hash` in the example below
+    ///
+    /// ```rust,ignore
+    /// use self::crypto_hash::{Algorithm, Hasher};
+    /// use crypto_hash;
+    /// ```
+    imports_as_use_self: Vec<Symbol>,
+}
+
+impl_lint_pass!(SingleComponentPathImports => [SINGLE_COMPONENT_PATH_IMPORTS]);
 
 impl EarlyLintPass for SingleComponentPathImports {
     fn check_item(&mut self, cx: &EarlyContext<'_>, item: &Item) {
+        if_chain! {
+            if !in_macro(item.span);
+            if cx.sess.opts.edition >= Edition::Edition2018;
+            if let ItemKind::Use(use_tree) = &item.kind;
+            if let segments = &use_tree.prefix.segments;
+            if segments[0].ident.name == sym!(self);
+
+            then {
+                // simple case such as `use self::module::SomeStruct`
+                if segments.len() > 1 {
+                    self.imports_as_use_self.push(segments[1].ident.name);
+                    return;
+                }
+
+                // nested case such as `use self::{module1::Struct1, module2::Struct2}`
+                if let UseTreeKind::Nested(trees) = &use_tree.kind {
+                    for tree in trees {
+                        let segments = &tree.0.prefix.segments;
+                        if !segments.is_empty() {
+                            self.imports_as_use_self.push(segments[0].ident.name);
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    fn check_item_post(&mut self, cx: &EarlyContext<'_>, item: &Item) {
         if_chain! {
             if !in_macro(item.span);
             if cx.sess.opts.edition >= Edition::Edition2018;
@@ -46,6 +87,8 @@ impl EarlyLintPass for SingleComponentPathImports {
             if let segments = &use_tree.prefix.segments;
             if segments.len() == 1;
             if let UseTreeKind::Simple(None, _, _) = use_tree.kind;
+            if !self.imports_as_use_self.contains(&segments[0].ident.name);
+
             then {
                 span_lint_and_sugg(
                     cx,
diff --git a/tests/ui/single_component_path_imports_self.rs b/tests/ui/single_component_path_imports_self.rs
new file mode 100644
index 000000000000..94319ade0ac4
--- /dev/null
+++ b/tests/ui/single_component_path_imports_self.rs
@@ -0,0 +1,16 @@
+// edition:2018
+#![warn(clippy::single_component_path_imports)]
+#![allow(unused_imports)]
+
+use self::regex::{Regex as xeger, RegexSet as tesxeger};
+pub use self::{
+    regex::{Regex, RegexSet},
+    some_mod::SomeType,
+};
+use regex;
+
+mod some_mod {
+    pub struct SomeType;
+}
+
+fn main() {}