Added the rest of the suggested changes.

Author: ofeeg

clippy_lints/src/methods/join_absolute_paths.rs

@@ -1,16 +1,16 @@
 use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::macros::HirNode;
 use clippy_utils::ty::is_type_diagnostic_item;
 use rustc_ast::ast::LitKind;
 use rustc_errors::Applicability;
 use rustc_hir::{Expr, ExprKind};
 use rustc_lint::LateContext;
 use rustc_span::symbol::sym::Path;
-use rustc_span::Span;
 
 use super::JOIN_ABSOLUTE_PATHS;
 
-pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>, join_arg: &'tcx Expr<'tcx>, span: Span) {
-    let ty = cx.typeck_results().expr_ty(expr);
+pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>, join_arg: &'tcx Expr<'tcx>) {
+    let ty = cx.typeck_results().expr_ty(expr).peel_refs();
     if !expr.span.from_expansion() {
         if is_type_diagnostic_item(cx, ty, Path) {
             let applicability = Applicability::MachineApplicable;
@@ -20,8 +20,8 @@ pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>, join_a
                         span_lint_and_sugg(
                             cx,
                             JOIN_ABSOLUTE_PATHS,
-                            span.with_hi(expr.span.hi()),
-                            r#"argument in join called on path contains a starting '/'"#,
+                            join_arg.span().with_hi(expr.span.hi()),
+                            r#"argument to `Path::join` starts with a path separator"#,
                             "try removing first '/' or '\\'",
                             "join(\"your/path/here\")".to_owned(),
                             applicability,

clippy_lints/src/methods/mod.rs

@@ -2975,8 +2975,8 @@ declare_clippy_lint! {
     /// # let mut state = DefaultHasher::new();
     /// # let my_enum = Foo::Empty;
     /// match my_enum {
-    /// 	Empty => ().hash(&mut state),
-    /// 	WithValue(x) => x.hash(&mut state),
+    ///         Empty => ().hash(&mut state),
+    ///         WithValue(x) => x.hash(&mut state),
     /// }
     /// ```
     /// Use instead:
@@ -2988,8 +2988,8 @@ declare_clippy_lint! {
     /// # let mut state = DefaultHasher::new();
     /// # let my_enum = Foo::Empty;
     /// match my_enum {
-    /// 	Empty => 0_u8.hash(&mut state),
-    /// 	WithValue(x) => x.hash(&mut state),
+    ///         Empty => 0_u8.hash(&mut state),
+    ///         WithValue(x) => x.hash(&mut state),
     /// }
     /// ```
     #[clippy::version = "1.58.0"]
@@ -3264,7 +3264,7 @@ declare_clippy_lint! {
 
 declare_clippy_lint! {
     /// ### What it does
-    /// Checks for initial `'/ or \\'` in an argument to `.join()` on a `Path`.
+    /// Checks for calls to `Path::join` that start with a path separator, like `\\` or `/`..
     ///
     /// ### Why is this bad?
     /// `.join()` comments starting with a separator  (`/` or `\\`) can replace the entire path.
@@ -3281,20 +3281,21 @@ declare_clippy_lint! {
     ///
     /// Use instead;
     /// ```rust
-    /// let path = std::path::Path::new("/bin");
+    /// # use std::path::{Path, PathBuf};
+    /// let path = Path::new("/bin");
     ///
     /// // If this was unintentional, remove the leading separator
-    /// let extend = path.join("sh");
-    /// assert_eq!(extend, std::path::PathBuf::from("/bin/sh"));
+    /// let joined_path = path.join("sh");
+    /// assert_eq!(joined_path, PathBuf::from("/bin/sh"));
     ///
     /// // If this was intentional, create a new path instead
-    /// let new = std::path::Path::new("/sh");
-    /// assert_eq!(new, std::path::PathBuf::from("/sh"));
+    /// let new = Path::new("/sh");
+    /// assert_eq!(new, PathBuf::from("/sh"));
     /// ```
     #[clippy::version = "1.70.0"]
     pub JOIN_ABSOLUTE_PATHS,
     pedantic,
-  "arg to .join called on a Path contains '/' at the start"
+  "arg to .join called on a Path contains separator at the start"
 }
 
 declare_clippy_lint! {
@@ -3869,7 +3870,9 @@ impl Methods {
                     if let Some(("collect", _, _, span, _)) = method_call(recv) {
                         unnecessary_join::check(cx, expr, recv, join_arg, span);
                     }
-                    else {join_absolute_paths::check(cx, expr,  join_arg, span);}
+                  else {
+                    join_absolute_paths::check(cx, recv,  join_arg);
+                  }
                 },
                 ("last", []) | ("skip", [_]) => {
                     if let Some((name2, recv2, args2, _span2, _)) = method_call(recv) {

tests/ui/join_absolute_paths.fixed

@@ -6,12 +6,12 @@ use std::path::Path;
 fn main() {
     // should be linted
     let path = Path::new("/bin");
-    path.join("/sh");
+    pathjoin("your/path/here")"/sh");
     println!("{}", path.display());
 
     //should be linted
     let path = Path::new("C:\\Users");
-    path.join("\\user");
+    pathjoin("your/path/here")"\\user");
     println!("{}", path.display());
 
     // should not be linted

tests/ui/join_absolute_paths.rs

@@ -1,4 +1,3 @@
-//@run-rustfix
 #![allow(unused)]
 #![warn(clippy::join_absolute_paths)]
 use std::path::Path;

tests/ui/join_absolute_paths.stderr

@@ -0,0 +1,16 @@
+error: argument to `Path::join` starts with a path separator
+  --> $DIR/join_absolute_paths.rs:8:9
+   |
+LL |     path.join("/sh");
+   |         ^^^^^^ help: try removing first '/' or '/': `join("your/path/here")`
+   |
+   = note: `-D clippy::join-absolute-paths` implied by `-D warnings`
+
+error: argument to `Path::join` starts with a path separator
+  --> $DIR/join_absolute_paths.rs:13:9
+   |
+LL |     path.join("//user");
+   |         ^^^^^^ help: try removing first '/' or '/': `join("your/path/here")`
+
+error: aborting due to 2 previous errors
+