Merge commit 'ff0993c5e9162ddaea78e83d0f0161e68bd4ea73' into clippy

clippy_lints/src/vec_resize_to_zero.rs

@@ -0,0 +1,59 @@
+use crate::utils::span_lint_and_then;
+use if_chain::if_chain;
+use rustc_errors::Applicability;
+use rustc_hir::{Expr, ExprKind};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+use rustc_span::source_map::Spanned;
+
+use crate::utils::{match_def_path, paths};
+use rustc_ast::ast::LitKind;
+use rustc_hir as hir;
+
+declare_clippy_lint! {
+    /// **What it does:** Finds occurences of `Vec::resize(0, an_int)`
+    ///
+    /// **Why is this bad?** This is probably an argument inversion mistake.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    /// ```rust
+    /// vec!(1, 2, 3, 4, 5).resize(0, 5)
+    /// ```
+    pub VEC_RESIZE_TO_ZERO,
+    correctness,
+    "emptying a vector with `resize(0, an_int)` instead of `clear()` is probably an argument inversion mistake"
+}
+
+declare_lint_pass!(VecResizeToZero => [VEC_RESIZE_TO_ZERO]);
+
+impl<'a, 'tcx> LateLintPass<'a, 'tcx> for VecResizeToZero {
+    fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
+        if_chain! {
+            if let hir::ExprKind::MethodCall(path_segment, _, ref args) = expr.kind;
+            if let Some(method_def_id) = cx.tables.type_dependent_def_id(expr.hir_id);
+            if match_def_path(cx, method_def_id, &paths::VEC_RESIZE) && args.len() == 3;
+            if let ExprKind::Lit(Spanned { node: LitKind::Int(0, _), .. }) = args[1].kind;
+            if let ExprKind::Lit(Spanned { node: LitKind::Int(..), .. }) = args[2].kind;
+            then {
+                let method_call_span = expr.span.with_lo(path_segment.ident.span.lo());
+                span_lint_and_then(
+                    cx,
+                    VEC_RESIZE_TO_ZERO,
+                    expr.span,
+                    "emptying a vector with `resize`",
+                    |db| {
+                        db.help("the arguments may be inverted...");
+                        db.span_suggestion(
+                            method_call_span,
+                            "...or you can empty the vector with",
+                            "clear()".to_string(),
+                            Applicability::MaybeIncorrect,
+                        );
+                    },
+                );
+            }
+        }
+    }
+}