Fix join_absolute_paths to work correctly depending on the platform (rust-lang#16610)

Fixes rust-lang#16607.

changelog: [`join_absolute_paths`]: remove both backslashes for calls to
`Path::join`.

Author: samueltardieu

clippy_lints/src/methods/join_absolute_paths.rs

@@ -2,7 +2,7 @@ use clippy_utils::diagnostics::span_lint_and_then;
 use clippy_utils::expr_or_init;
 use clippy_utils::res::MaybeDef;
 use clippy_utils::source::snippet;
-use rustc_ast::ast::LitKind;
+use rustc_ast::ast::{LitKind, StrStyle};
 use rustc_errors::Applicability;
 use rustc_hir::{Expr, ExprKind};
 use rustc_lint::LateContext;
@@ -15,7 +15,7 @@ pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, recv: &'tcx Expr<'tcx>, join_a
     let ty = cx.typeck_results().expr_ty(recv).peel_refs();
     if matches!(ty.opt_diag_name(cx), Some(sym::Path | sym::PathBuf))
         && let ExprKind::Lit(spanned) = expr_or_init(cx, join_arg).kind
-        && let LitKind::Str(symbol, _) = spanned.node
+        && let LitKind::Str(symbol, style) = spanned.node
         && let sym_str = symbol.as_str()
         && sym_str.starts_with(['/', '\\'])
     {
@@ -29,8 +29,10 @@ pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, recv: &'tcx Expr<'tcx>, join_a
 
                 let no_separator = if sym_str.starts_with('/') {
                     arg_str.replacen('/', "", 1)
-                } else {
+                } else if let StrStyle::Raw(_) = style {
                     arg_str.replacen('\\', "", 1)
+                } else {
+                    arg_str.replacen("\\\\", "", 1)
                 };
 
                 diag.note("joining a path starting with separator will replace the path instead")

tests/ui/join_absolute_paths.1.fixed

@@ -0,0 +1,36 @@
+#![allow(clippy::needless_raw_string_hashes)]
+#![warn(clippy::join_absolute_paths)]
+
+use std::path::{Path, PathBuf};
+
+fn main() {
+    let path = Path::new("/bin");
+    path.join("sh");
+    //~^ join_absolute_paths
+
+    let path = PathBuf::from("/bin");
+    path.join("sh");
+    //~^ join_absolute_paths
+
+    let path = PathBuf::from("/bin");
+    path.join(r#"sh"#);
+    //~^ join_absolute_paths
+
+    let path = Path::new("C:\\Users");
+    path.join("user");
+    //~^ join_absolute_paths
+
+    let path = PathBuf::from("C:\\Users");
+    path.join("user");
+    //~^ join_absolute_paths
+
+    let path = PathBuf::from("C:\\Users");
+    path.join(r#"user"#);
+    //~^ join_absolute_paths
+
+    let path: &[&str] = &["/bin"];
+    path.join("/sh");
+
+    let path = Path::new("/bin");
+    path.join("sh");
+}

tests/ui/join_absolute_paths.2.fixed

@@ -0,0 +1,36 @@
+#![allow(clippy::needless_raw_string_hashes)]
+#![warn(clippy::join_absolute_paths)]
+
+use std::path::{Path, PathBuf};
+
+fn main() {
+    let path = Path::new("/bin");
+    PathBuf::from("/sh");
+    //~^ join_absolute_paths
+
+    let path = PathBuf::from("/bin");
+    PathBuf::from("/sh");
+    //~^ join_absolute_paths
+
+    let path = PathBuf::from("/bin");
+    PathBuf::from(r#"/sh"#);
+    //~^ join_absolute_paths
+
+    let path = Path::new("C:\\Users");
+    PathBuf::from("\\user");
+    //~^ join_absolute_paths
+
+    let path = PathBuf::from("C:\\Users");
+    PathBuf::from("\\user");
+    //~^ join_absolute_paths
+
+    let path = PathBuf::from("C:\\Users");
+    PathBuf::from(r#"\user"#);
+    //~^ join_absolute_paths
+
+    let path: &[&str] = &["/bin"];
+    path.join("/sh");
+
+    let path = Path::new("/bin");
+    path.join("sh");
+}

tests/ui/join_absolute_paths.rs

@@ -1,5 +1,3 @@
-//@no-rustfix
-
 #![allow(clippy::needless_raw_string_hashes)]
 #![warn(clippy::join_absolute_paths)]
 
@@ -10,10 +8,6 @@ fn main() {
     path.join("/sh");
     //~^ join_absolute_paths
 
-    let path = Path::new("C:\\Users");
-    path.join("\\user");
-    //~^ join_absolute_paths
-
     let path = PathBuf::from("/bin");
     path.join("/sh");
     //~^ join_absolute_paths
@@ -22,6 +16,18 @@ fn main() {
     path.join(r#"/sh"#);
     //~^ join_absolute_paths
 
+    let path = Path::new("C:\\Users");
+    path.join("\\user");
+    //~^ join_absolute_paths
+
+    let path = PathBuf::from("C:\\Users");
+    path.join("\\user");
+    //~^ join_absolute_paths
+
+    let path = PathBuf::from("C:\\Users");
+    path.join(r#"\user"#);
+    //~^ join_absolute_paths
+
     let path: &[&str] = &["/bin"];
     path.join("/sh");
 

tests/ui/join_absolute_paths.stderr

@@ -1,5 +1,5 @@
 error: argument to `Path::join` starts with a path separator
-  --> tests/ui/join_absolute_paths.rs:10:15
+  --> tests/ui/join_absolute_paths.rs:8:15
    |
 LL |     path.join("/sh");
    |               ^^^^^
@@ -19,7 +19,43 @@ LL +     PathBuf::from("/sh");
    |
 
 error: argument to `Path::join` starts with a path separator
-  --> tests/ui/join_absolute_paths.rs:14:15
+  --> tests/ui/join_absolute_paths.rs:12:15
+   |
+LL |     path.join("/sh");
+   |               ^^^^^
+   |
+   = note: joining a path starting with separator will replace the path instead
+help: if this is unintentional, try removing the starting separator
+   |
+LL -     path.join("/sh");
+LL +     path.join("sh");
+   |
+help: if this is intentional, consider using `Path::new`
+   |
+LL -     path.join("/sh");
+LL +     PathBuf::from("/sh");
+   |
+
+error: argument to `Path::join` starts with a path separator
+  --> tests/ui/join_absolute_paths.rs:16:15
+   |
+LL |     path.join(r#"/sh"#);
+   |               ^^^^^^^^
+   |
+   = note: joining a path starting with separator will replace the path instead
+help: if this is unintentional, try removing the starting separator
+   |
+LL -     path.join(r#"/sh"#);
+LL +     path.join(r#"sh"#);
+   |
+help: if this is intentional, consider using `Path::new`
+   |
+LL -     path.join(r#"/sh"#);
+LL +     PathBuf::from(r#"/sh"#);
+   |
+
+error: argument to `Path::join` starts with a path separator
+  --> tests/ui/join_absolute_paths.rs:20:15
    |
 LL |     path.join("\\user");
    |               ^^^^^^^^
@@ -28,7 +64,7 @@ LL |     path.join("\\user");
 help: if this is unintentional, try removing the starting separator
    |
 LL -     path.join("\\user");
-LL +     path.join("\user");
+LL +     path.join("user");
    |
 help: if this is intentional, consider using `Path::new`
    |
@@ -37,40 +73,40 @@ LL +     PathBuf::from("\\user");
    |
 
 error: argument to `Path::join` starts with a path separator
-  --> tests/ui/join_absolute_paths.rs:18:15
+  --> tests/ui/join_absolute_paths.rs:24:15
    |
-LL |     path.join("/sh");
-   |               ^^^^^
+LL |     path.join("\\user");
+   |               ^^^^^^^^
    |
    = note: joining a path starting with separator will replace the path instead
 help: if this is unintentional, try removing the starting separator
    |
-LL -     path.join("/sh");
-LL +     path.join("sh");
+LL -     path.join("\\user");
+LL +     path.join("user");
    |
 help: if this is intentional, consider using `Path::new`
    |
-LL -     path.join("/sh");
-LL +     PathBuf::from("/sh");
+LL -     path.join("\\user");
+LL +     PathBuf::from("\\user");
    |
 
 error: argument to `Path::join` starts with a path separator
-  --> tests/ui/join_absolute_paths.rs:22:15
+  --> tests/ui/join_absolute_paths.rs:28:15
    |
-LL |     path.join(r#"/sh"#);
-   |               ^^^^^^^^
+LL |     path.join(r#"\user"#);
+   |               ^^^^^^^^^^
    |
    = note: joining a path starting with separator will replace the path instead
 help: if this is unintentional, try removing the starting separator
    |
-LL -     path.join(r#"/sh"#);
-LL +     path.join(r#"sh"#);
+LL -     path.join(r#"\user"#);
+LL +     path.join(r#"user"#);
    |
 help: if this is intentional, consider using `Path::new`
    |
-LL -     path.join(r#"/sh"#);
-LL +     PathBuf::from(r#"/sh"#);
+LL -     path.join(r#"\user"#);
+LL +     PathBuf::from(r#"\user"#);
    |
 
-error: aborting due to 4 previous errors
+error: aborting due to 6 previous errors