New lint clippy::join_absolute_paths

CHANGELOG.md

@@ -5037,6 +5037,7 @@ Released 2018-09-13
 [`iter_skip_zero`]: https://rust-lang.github.io/rust-clippy/master/index.html#iter_skip_zero
 [`iter_with_drain`]: https://rust-lang.github.io/rust-clippy/master/index.html#iter_with_drain
 [`iterator_step_by_zero`]: https://rust-lang.github.io/rust-clippy/master/index.html#iterator_step_by_zero
+[`join_absolute_paths`]: https://rust-lang.github.io/rust-clippy/master/index.html#join_absolute_paths
 [`just_underscores_and_digits`]: https://rust-lang.github.io/rust-clippy/master/index.html#just_underscores_and_digits
 [`large_const_arrays`]: https://rust-lang.github.io/rust-clippy/master/index.html#large_const_arrays
 [`large_digit_groups`]: https://rust-lang.github.io/rust-clippy/master/index.html#large_digit_groups

clippy_lints/src/declared_lints.rs

@@ -369,6 +369,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::methods::ITER_SKIP_NEXT_INFO,
     crate::methods::ITER_SKIP_ZERO_INFO,
     crate::methods::ITER_WITH_DRAIN_INFO,
+    crate::methods::JOIN_ABSOLUTE_PATHS_INFO,
     crate::methods::MANUAL_FILTER_MAP_INFO,
     crate::methods::MANUAL_FIND_MAP_INFO,
     crate::methods::MANUAL_NEXT_BACK_INFO,

clippy_lints/src/methods/join_absolute_paths.rs

@@ -0,0 +1,30 @@
+use clippy_utils::diagnostics::span_lint_and_then;
+use clippy_utils::ty::is_type_diagnostic_item;
+use rustc_ast::ast::LitKind;
+use rustc_hir::{Expr, ExprKind};
+use rustc_lint::LateContext;
+use rustc_span::symbol::sym::Path;
+
+use super::JOIN_ABSOLUTE_PATHS;
+
+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 is_type_diagnostic_item(cx, ty, Path)
+        && let ExprKind::Lit(spanned) = &join_arg.kind
+        && let LitKind::Str(symbol, _) = spanned.node
+        && (symbol.as_str().starts_with('/') || symbol.as_str().starts_with('\\'))
+    {
+        span_lint_and_then(
+            cx,
+            JOIN_ABSOLUTE_PATHS,
+            join_arg.span,
+            "argument to `Path::join` starts with a path separator",
+            |diag| {
+                diag
+                      .note("joining a path starting with separator will replace the path instead")
+                      .help("if this is unintentional, try removing the starting separator")
+                      .help("if this is intentional, try creating a new Path instead");
+            },
+        );
+    }
+}

clippy_lints/src/methods/mod.rs

@@ -49,6 +49,7 @@ mod iter_skip_next;
 mod iter_skip_zero;
 mod iter_with_drain;
 mod iterator_step_by_zero;
+mod join_absolute_paths;
 mod manual_next_back;
 mod manual_ok_or;
 mod manual_saturating_arithmetic;
@@ -3631,6 +3632,42 @@ declare_clippy_lint! {
     "`as_str` used to call a method on `str` that is also available on `String`"
 }
 
+declare_clippy_lint! {
+    /// Checks for calls to `Path::join` that start with a path separator, like `\\` or `/`..
+    ///
+    /// ### Why is this bad?
+    /// `.join()` arguments starting with a separator  (`/` or `\\`) can replace the entire path.
+    /// If this is intentional, prefer using `Path::new()` instead.
+    ///
+    /// See [`Path::join()`](https://doc.rust-lang.org/std/path/struct.Path.html#method.join)
+    ///
+    /// ### Example
+    /// ```rust
+    /// # use std::path::{Path, PathBuf};
+    /// let path = Path::new("/bin");
+    /// let joined_path = path.join("/sh");
+    /// assert_eq!(joined_path, PathBuf::from("/sh"));
+    /// ```
+    ///
+    /// Use instead;
+    /// ```rust
+    /// # use std::path::{Path, PathBuf};
+    /// let path = Path::new("/bin");
+    ///
+    /// // If this was unintentional, remove the leading separator
+    /// 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 = Path::new("/sh");
+    /// assert_eq!(new, PathBuf::from("/sh"));
+    /// ```
+    #[clippy::version = "1.74.0"]
+    pub JOIN_ABSOLUTE_PATHS,
+    correctness,
+    "arg to .join called on a `Path` contains leading separator"
+}
+
 pub struct Methods {
     avoid_breaking_exported_api: bool,
     msrv: Msrv,
@@ -3776,6 +3813,7 @@ impl_lint_pass!(Methods => [
     ITER_OUT_OF_BOUNDS,
     PATH_ENDS_WITH_EXT,
     REDUNDANT_AS_STR,
+    JOIN_ABSOLUTE_PATHS,
 ]);
 
 /// Extracts a method call name, args, and `Span` of the method name.
@@ -4139,6 +4177,8 @@ impl Methods {
                 ("join", [join_arg]) => {
                     if let Some(("collect", _, _, span, _)) = method_call(recv) {
                         unnecessary_join::check(cx, expr, recv, join_arg, span);
+                    } else {
+                        join_absolute_paths::check(cx, recv, join_arg);
                     }
                 },
                 ("last", []) => {

tests/ui/join_absolute_paths.rs

@@ -0,0 +1,26 @@
+#![allow(unused)]
+#![warn(clippy::join_absolute_paths)]
+
+use std::path::{Path, PathBuf};
+
+fn main() {
+    // should be linted
+    let path = Path::new("/bin");
+    path.join("/sh");
+
+    // should be linted
+    let path = Path::new("C:\\Users");
+    path.join("\\user");
+
+    // should not be linted
+    let path: &[&str] = &["/bin"];
+    path.join("/sh");
+
+    // should not be linted
+    let path = Path::new("/bin");
+    path.join("sh");
+
+    // should be linted
+    let path = PathBuf::from("/bin");
+    path.join("/sh");
+}

tests/ui/join_absolute_paths.stderr

@@ -0,0 +1,23 @@
+error: argument to `Path::join` starts with a path separator
+  --> $DIR/join_absolute_paths.rs:9:15
+   |
+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
+   = help: if this is intentional, try creating a new Path instead
+   = 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:13:15
+   |
+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
+   = help: if this is intentional, try creating a new Path instead
+
+error: aborting due to 2 previous errors
+