Move VecResizeToZero into Methods lint pass

Author: Jarcho

clippy_lints/src/lib.register_all.rs

@@ -217,6 +217,7 @@ store.register_group(true, "clippy::all", Some("clippy_all"), vec![
     LintId::of(methods::UNNECESSARY_TO_OWNED),
     LintId::of(methods::UNWRAP_OR_ELSE_DEFAULT),
     LintId::of(methods::USELESS_ASREF),
+    LintId::of(methods::VEC_RESIZE_TO_ZERO),
     LintId::of(methods::WRONG_SELF_CONVENTION),
     LintId::of(methods::ZST_OFFSET),
     LintId::of(minmax::MIN_MAX),
@@ -343,7 +344,6 @@ store.register_group(true, "clippy::all", Some("clippy_all"), vec![
     LintId::of(useless_conversion::USELESS_CONVERSION),
     LintId::of(vec::USELESS_VEC),
     LintId::of(vec_init_then_push::VEC_INIT_THEN_PUSH),
-    LintId::of(vec_resize_to_zero::VEC_RESIZE_TO_ZERO),
     LintId::of(write::PRINTLN_EMPTY_STRING),
     LintId::of(write::PRINT_LITERAL),
     LintId::of(write::PRINT_WITH_NEWLINE),

clippy_lints/src/lib.register_correctness.rs

@@ -43,6 +43,7 @@ store.register_group(true, "clippy::correctness", Some("clippy_correctness"), ve
     LintId::of(methods::SUSPICIOUS_SPLITN),
     LintId::of(methods::UNINIT_ASSUMED_INIT),
     LintId::of(methods::UNIT_HASH),
+    LintId::of(methods::VEC_RESIZE_TO_ZERO),
     LintId::of(methods::ZST_OFFSET),
     LintId::of(minmax::MIN_MAX),
     LintId::of(non_octal_unix_permissions::NON_OCTAL_UNIX_PERMISSIONS),
@@ -74,5 +75,4 @@ store.register_group(true, "clippy::correctness", Some("clippy_correctness"), ve
     LintId::of(unnamed_address::VTABLE_ADDRESS_COMPARISONS),
     LintId::of(unused_io_amount::UNUSED_IO_AMOUNT),
     LintId::of(unwrap::PANICKING_UNWRAP),
-    LintId::of(vec_resize_to_zero::VEC_RESIZE_TO_ZERO),
 ])

clippy_lints/src/lib.register_lints.rs

@@ -363,6 +363,7 @@ store.register_lints(&[
     methods::UNWRAP_OR_ELSE_DEFAULT,
     methods::UNWRAP_USED,
     methods::USELESS_ASREF,
+    methods::VEC_RESIZE_TO_ZERO,
     methods::WRONG_SELF_CONVENTION,
     methods::ZST_OFFSET,
     minmax::MIN_MAX,
@@ -573,7 +574,6 @@ store.register_lints(&[
     useless_conversion::USELESS_CONVERSION,
     vec::USELESS_VEC,
     vec_init_then_push::VEC_INIT_THEN_PUSH,
-    vec_resize_to_zero::VEC_RESIZE_TO_ZERO,
     verbose_file_reads::VERBOSE_FILE_READS,
     wildcard_imports::ENUM_GLOB_USE,
     wildcard_imports::WILDCARD_IMPORTS,

clippy_lints/src/lib.rs

@@ -387,7 +387,6 @@ mod use_self;
 mod useless_conversion;
 mod vec;
 mod vec_init_then_push;
-mod vec_resize_to_zero;
 mod verbose_file_reads;
 mod wildcard_imports;
 mod write;
@@ -787,7 +786,6 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     store.register_late_pass(|| Box::new(if_not_else::IfNotElse));
     store.register_late_pass(|| Box::new(equatable_if_let::PatternEquality));
     store.register_late_pass(|| Box::new(manual_async_fn::ManualAsyncFn));
-    store.register_late_pass(|| Box::new(vec_resize_to_zero::VecResizeToZero));
     store.register_late_pass(|| Box::new(panic_in_result_fn::PanicInResultFn));
     let single_char_binding_names_threshold = conf.single_char_binding_names_threshold;
     store.register_early_pass(move || {

clippy_lints/src/methods/mod.rs

@@ -88,6 +88,7 @@ mod unwrap_or_else_default;
 mod unwrap_used;
 mod useless_asref;
 mod utils;
+mod vec_resize_to_zero;
 mod wrong_self_convention;
 mod zst_offset;
 
@@ -2796,6 +2797,28 @@ declare_clippy_lint! {
     "Use of `Vec::sort_by` when `Vec::sort_by_key` or `Vec::sort` would be clearer"
 }
 
+declare_clippy_lint! {
+    /// ### What it does
+    /// Finds occurrences of `Vec::resize(0, an_int)`
+    ///
+    /// ### Why is this bad?
+    /// This is probably an argument inversion mistake.
+    ///
+    /// ### Example
+    /// ```rust
+    /// vec!(1, 2, 3, 4, 5).resize(0, 5)
+    /// ```
+    ///
+    /// Use instead:
+    /// ```rust
+    /// vec!(1, 2, 3, 4, 5).clear()
+    /// ```
+    #[clippy::version = "1.46.0"]
+    pub VEC_RESIZE_TO_ZERO,
+    correctness,
+    "emptying a vector with `resize(0, an_int)` instead of `clear()` is probably an argument inversion mistake"
+}
+
 pub struct Methods {
     avoid_breaking_exported_api: bool,
     msrv: Option<RustcVersion>,
@@ -2912,6 +2935,7 @@ impl_lint_pass!(Methods => [
     STABLE_SORT_PRIMITIVE,
     UNIT_HASH,
     UNNECESSARY_SORT_BY,
+    VEC_RESIZE_TO_ZERO,
 ]);
 
 /// Extracts a method call name, args, and `Span` of the method name.
@@ -3302,6 +3326,9 @@ impl Methods {
                 ("repeat", [arg]) => {
                     repeat_once::check(cx, expr, recv, arg);
                 },
+                ("resize", [count_arg, default_arg]) => {
+                    vec_resize_to_zero::check(cx, expr, count_arg, default_arg, span);
+                },
                 ("sort", []) => {
                     stable_sort_primitive::check(cx, expr, recv);
                 },

clippy_lints/src/methods/vec_resize_to_zero.rs

@@ -0,0 +1,45 @@
+use clippy_utils::diagnostics::span_lint_and_then;
+use clippy_utils::ty::is_type_diagnostic_item;
+use if_chain::if_chain;
+use rustc_ast::LitKind;
+use rustc_errors::Applicability;
+use rustc_hir::{Expr, ExprKind};
+use rustc_lint::LateContext;
+use rustc_span::source_map::Spanned;
+use rustc_span::{sym, Span};
+
+use super::VEC_RESIZE_TO_ZERO;
+
+pub(super) fn check<'tcx>(
+    cx: &LateContext<'tcx>,
+    expr: &'tcx Expr<'_>,
+    count_arg: &'tcx Expr<'_>,
+    default_arg: &'tcx Expr<'_>,
+    name_span: Span,
+) {
+    if_chain! {
+        if let Some(method_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
+        if let Some(impl_id) = cx.tcx.impl_of_method(method_id);
+        if is_type_diagnostic_item(cx, cx.tcx.type_of(impl_id), sym::Vec);
+        if let ExprKind::Lit(Spanned { node: LitKind::Int(0, _), .. }) = count_arg.kind;
+        if let ExprKind::Lit(Spanned { node: LitKind::Int(..), .. }) = default_arg.kind;
+        then {
+            let method_call_span = expr.span.with_lo(name_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,
+                    );
+                },
+            );
+        }
+    }
+}

clippy_lints/src/vec_resize_to_zero.rs

@@ -1,15 +1,19 @@
 #![warn(clippy::vec_resize_to_zero)]
 
 fn main() {
+    let mut v = vec![1, 2, 3, 4, 5];
+
     // applicable here
-    vec![1, 2, 3, 4, 5].resize(0, 5);
+    v.resize(0, 5);
 
     // not applicable
-    vec![1, 2, 3, 4, 5].resize(2, 5);
+    v.resize(2, 5);
+
+    let mut v = vec!["foo", "bar", "baz"];
 
     // applicable here, but only implemented for integer literals for now
-    vec!["foo", "bar", "baz"].resize(0, "bar");
+    v.resize(0, "bar");
 
     // not applicable
-    vec!["foo", "bar", "baz"].resize(2, "bar")
+    v.resize(2, "bar")
 }

tests/ui/vec_resize_to_zero.rs

@@ -1,10 +1,10 @@
 error: emptying a vector with `resize`
-  --> $DIR/vec_resize_to_zero.rs:5:5
+  --> $DIR/vec_resize_to_zero.rs:7:5
    |
-LL |     vec![1, 2, 3, 4, 5].resize(0, 5);
-   |     ^^^^^^^^^^^^^^^^^^^^------------
-   |                         |
-   |                         help: ...or you can empty the vector with: `clear()`
+LL |     v.resize(0, 5);
+   |     ^^------------
+   |       |
+   |       help: ...or you can empty the vector with: `clear()`
    |
    = note: `-D clippy::vec-resize-to-zero` implied by `-D warnings`
    = help: the arguments may be inverted...