Added new lint "path_join_correction"

CHANGELOG.md

@@ -4747,6 +4747,7 @@ Released 2018-09-13
 [`iter_skip_next`]: https://rust-lang.github.io/rust-clippy/master/index.html#iter_skip_next
 [`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_path`]: https://rust-lang.github.io/rust-clippy/master/index.html#join_absolute_path
 [`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

@@ -350,6 +350,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::methods::ITER_OVEREAGER_CLONED_INFO,
     crate::methods::ITER_SKIP_NEXT_INFO,
     crate::methods::ITER_WITH_DRAIN_INFO,
+    crate::methods::JOIN_ABSOLUTE_PATH_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_path.rs

@@ -0,0 +1,30 @@
+use clippy_utils::{diagnostics::span_lint_and_sugg, 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, Span};
+
+use super::JOIN_ABSOLUTE_PATH;
+
+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);
+    if_chain!(
+     if is_type_diagnostic_item(cx, ty, Path);
+     let applicability = Applicability::MachineApplicable;
+     if let ExprKind::Lit(spanned) = &join_arg.kind;
+     if let LitKind::Str(symbol, _) = spanned.node;
+     if symbol.as_str().starts_with('/') || symbol.as_str().starts_with('\\');
+     then {
+      span_lint_and_sugg(
+      cx,
+      JOIN_ABSOLUTE_PATH,
+      span.with_hi(expr.span.hi()),
+      r#"argument in join called on path contains a starting '/'"#,
+      "try removing first '/' or '\\'",
+      "join(\"your/path/here\")".to_owned(),
+      applicability
+      );
+     }
+    );
+}

clippy_lints/src/methods/mod.rs

@@ -45,6 +45,7 @@ mod iter_overeager_cloned;
 mod iter_skip_next;
 mod iter_with_drain;
 mod iterator_step_by_zero;
+mod join_absolute_path;
 mod manual_next_back;
 mod manual_ok_or;
 mod manual_saturating_arithmetic;
@@ -3194,6 +3195,41 @@ declare_clippy_lint! {
     "calling `drain` in order to `clear` a container"
 }
 
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for initial `'/'` in an argument to `.join()` on a `Path`.
+    ///
+    /// ### Why is this bad?
+    /// `.join()` comments starting with a separator, can replace the entire path.
+    /// If this is intentional, prefer creating a new `Path` instead.
+    ///
+    /// See [`Path::join()`](https://doc.rust-lang.org/std/path/struct.Path.html#method.join)
+    ///
+    /// ### Example
+    /// ```rust
+    /// let path = std::path::Path::new("/bin");
+    /// let res = path.join("/sh");
+    /// assert_eq!(res, std::path::PathBuf::from("/sh"));
+    /// ```
+    ///
+    /// Use instead;
+    /// ```rust
+    /// let path = std::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"));
+    ///
+    /// // If this was intentional, create a new path instead
+    /// let new = std::path::Path::new("/sh");
+    /// assert_eq!(new, std::path::PathBuf::from("/sh"));
+    /// ```
+    #[clippy::version = "1.70.0"]
+    pub JOIN_ABSOLUTE_PATH,
+    pedantic,
+  "arg to .join called on a Path contains '/' at the start"
+}
+
 declare_clippy_lint! {
     /// ### What it does
     /// Checks for `.rev().next()` on a `DoubleEndedIterator`
@@ -3345,6 +3381,7 @@ impl_lint_pass!(Methods => [
     NEEDLESS_COLLECT,
     SUSPICIOUS_COMMAND_ARG_SPACE,
     CLEAR_WITH_DRAIN,
+    JOIN_ABSOLUTE_PATH,
     MANUAL_NEXT_BACK,
 ]);
 
@@ -3654,6 +3691,7 @@ impl Methods {
                     if let Some(("collect", _, _, span, _)) = method_call(recv) {
                         unnecessary_join::check(cx, expr, recv, join_arg, span);
                     }
+                    else {join_absolute_path::check(cx, expr,  join_arg, span);}
                 },
                 ("last", []) | ("skip", [_]) => {
                     if let Some((name2, recv2, args2, _span2, _)) = method_call(recv) {

tests/ui/join_absolute_path.rs

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