Auto merge of #11453 - xFrednet:11208-path-join-correct, r=blyxyas

New lint `clippy::join_absolute_paths`

Hey `@ofeeg,` this PR is a copy of all the changes you did in https://github.com/rust-lang/rust-clippy/commit/47171d3c6366dd08476b2ab1e1661950d13a4218 from PR https://github.com/rust-lang/rust-clippy/pull/11208. I wasn't sure how to fix the git history. Hope you're okay with me figuring this out in this separate PR

---

changelog: New lint [`join_absolute_paths`]
[#11453](https://github.com/rust-lang/rust-clippy/pull/11453)

Closes: https://github.com/rust-lang/rust-clippy/issues/10655

r? `@Centri3` Since you also gave feedback on the other PR. I hope that I copied everything correctly, but a third pair of eyes would be appreciated :D

2 files changed, 98 insertions, 0 deletions

diff --git a/tests/ui/join_absolute_paths.rs b/tests/ui/join_absolute_paths.rs
new file mode 100644
index 00000000000..efa77a0492e
--- /dev/null
+++ b/tests/ui/join_absolute_paths.rs
@@ -0,0 +1,30 @@
+//@no-rustfix
+
+#![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");
+    //~^ ERROR: argument to `Path::join` starts with a path separator
+
+    let path = Path::new("C:\\Users");
+    path.join("\\user");
+    //~^ ERROR: argument to `Path::join` starts with a path separator
+
+    let path = PathBuf::from("/bin");
+    path.join("/sh");
+    //~^ ERROR: argument to `Path::join` starts with a path separator
+
+    let path = PathBuf::from("/bin");
+    path.join(r#"/sh"#);
+    //~^ ERROR: argument to `Path::join` starts with a path separator
+
+    let path: &[&str] = &["/bin"];
+    path.join("/sh");
+
+    let path = Path::new("/bin");
+    path.join("sh");
+}
diff --git a/tests/ui/join_absolute_paths.stderr b/tests/ui/join_absolute_paths.stderr
new file mode 100644
index 00000000000..0c2f89d9978
--- /dev/null
+++ b/tests/ui/join_absolute_paths.stderr
@@ -0,0 +1,68 @@
+error: argument to `Path::join` starts with a path separator
+  --> $DIR/join_absolute_paths.rs:10:15
+   |
+LL |     path.join("/sh");
+   |               ^^^^^
+   |
+   = note: joining a path starting with separator will replace the path instead
+   = note: `-D clippy::join-absolute-paths` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::join_absolute_paths)]`
+help: if this is unintentional, try removing the starting separator
+   |
+LL |     path.join("sh");
+   |               ~~~~
+help: if this is intentional, try using `Path::new` instead
+   |
+LL |     PathBuf::from("/sh");
+   |     ~~~~~~~~~~~~~~~~~~~~
+
+error: argument to `Path::join` starts with a path separator
+  --> $DIR/join_absolute_paths.rs:14:15
+   |
+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("\user");
+   |               ~~~~~~~
+help: if this is intentional, try using `Path::new` instead
+   |
+LL |     PathBuf::from("\\user");
+   |     ~~~~~~~~~~~~~~~~~~~~~~~
+
+error: argument to `Path::join` starts with a path separator
+  --> $DIR/join_absolute_paths.rs:18:15
+   |
+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");
+   |               ~~~~
+help: if this is intentional, try using `Path::new` instead
+   |
+LL |     PathBuf::from("/sh");
+   |     ~~~~~~~~~~~~~~~~~~~~
+
+error: argument to `Path::join` starts with a path separator
+  --> $DIR/join_absolute_paths.rs:22:15
+   |
+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"#);
+   |               ~~~~~~~
+help: if this is intentional, try using `Path::new` instead
+   |
+LL |     PathBuf::from(r#"/sh"#);
+   |     ~~~~~~~~~~~~~~~~~~~~~~~
+
+error: aborting due to 4 previous errors
+