Add lint manual_str_repeat

CHANGELOG.md

@@ -2493,6 +2493,7 @@ Released 2018-09-13
 [`manual_ok_or`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_ok_or
 [`manual_range_contains`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_range_contains
 [`manual_saturating_arithmetic`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_saturating_arithmetic
+[`manual_str_repeat`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_str_repeat
 [`manual_strip`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_strip
 [`manual_swap`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_swap
 [`manual_unwrap_or`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_unwrap_or

clippy_lints/src/lib.rs

@@ -762,6 +762,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         methods::MANUAL_FILTER_MAP,
         methods::MANUAL_FIND_MAP,
         methods::MANUAL_SATURATING_ARITHMETIC,
+        methods::MANUAL_STR_REPEAT,
         methods::MAP_COLLECT_RESULT_UNIT,
         methods::MAP_FLATTEN,
         methods::MAP_UNWRAP_OR,
@@ -1298,6 +1299,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(methods::MANUAL_FILTER_MAP),
         LintId::of(methods::MANUAL_FIND_MAP),
         LintId::of(methods::MANUAL_SATURATING_ARITHMETIC),
+        LintId::of(methods::MANUAL_STR_REPEAT),
         LintId::of(methods::MAP_COLLECT_RESULT_UNIT),
         LintId::of(methods::NEW_RET_NO_SELF),
         LintId::of(methods::OK_EXPECT),
@@ -1735,6 +1737,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(loops::NEEDLESS_COLLECT),
         LintId::of(methods::EXPECT_FUN_CALL),
         LintId::of(methods::ITER_NTH),
+        LintId::of(methods::MANUAL_STR_REPEAT),
         LintId::of(methods::OR_FUN_CALL),
         LintId::of(methods::SINGLE_CHAR_PATTERN),
         LintId::of(misc::CMP_OWNED),

clippy_lints/src/mem_discriminant.rs

@@ -7,7 +7,6 @@ use rustc_errors::Applicability;
 use rustc_hir::{BorrowKind, Expr, ExprKind};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::{declare_lint_pass, declare_tool_lint};
-use std::iter;
 
 declare_clippy_lint! {
     /// **What it does:** Checks for calls of `mem::discriminant()` on a non-enum type.
@@ -67,7 +66,7 @@ impl<'tcx> LateLintPass<'tcx> for MemDiscriminant {
                                 }
                             }
 
-                            let derefs: String = iter::repeat('*').take(derefs_needed).collect();
+                            let derefs = "*".repeat(derefs_needed);
                             diag.span_suggestion(
                                 param.span,
                                 "try dereferencing",

clippy_lints/src/methods/clone_on_copy.rs

@@ -8,7 +8,6 @@ use rustc_hir::{BindingAnnotation, Expr, ExprKind, MatchSource, Node, PatKind};
 use rustc_lint::LateContext;
 use rustc_middle::ty::{self, adjustment::Adjust};
 use rustc_span::symbol::{sym, Symbol};
-use std::iter;
 
 use super::CLONE_DOUBLE_REF;
 use super::CLONE_ON_COPY;
@@ -54,8 +53,8 @@ pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, method_name: Symbol,
                             ty = inner;
                             n += 1;
                         }
-                        let refs: String = iter::repeat('&').take(n + 1).collect();
-                        let derefs: String = iter::repeat('*').take(n).collect();
+                        let refs = "&".repeat(n + 1);
+                        let derefs = "*".repeat(n);
                         let explicit = format!("<{}{}>::clone({})", refs, ty, snip);
                         diag.span_suggestion(
                             expr.span,

clippy_lints/src/methods/manual_str_repeat.rs

@@ -0,0 +1,99 @@
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::source::{snippet_with_applicability, snippet_with_context};
+use clippy_utils::sugg::Sugg;
+use clippy_utils::ty::{is_type_diagnostic_item, is_type_lang_item, match_type};
+use clippy_utils::{is_expr_path_def_path, paths};
+use if_chain::if_chain;
+use rustc_ast::LitKind;
+use rustc_errors::Applicability;
+use rustc_hir::{Expr, ExprKind, LangItem};
+use rustc_lint::LateContext;
+use rustc_middle::ty::{self, Ty, TyS};
+use rustc_span::symbol::sym;
+use std::borrow::Cow;
+
+use super::MANUAL_STR_REPEAT;
+
+enum RepeatKind {
+    String,
+    Char(char),
+}
+
+fn get_ty_param(ty: Ty<'_>) -> Option<Ty<'_>> {
+    if let ty::Adt(_, subs) = ty.kind() {
+        subs.types().next()
+    } else {
+        None
+    }
+}
+
+fn parse_repeat_arg(cx: &LateContext<'_>, e: &Expr<'_>) -> Option<RepeatKind> {
+    if let ExprKind::Lit(lit) = &e.kind {
+        match lit.node {
+            LitKind::Str(..) => Some(RepeatKind::String),
+            LitKind::Char(c) => Some(RepeatKind::Char(c)),
+            _ => None,
+        }
+    } else {
+        let ty = cx.typeck_results().expr_ty(e);
+        if is_type_diagnostic_item(cx, ty, sym::string_type)
+            || (is_type_lang_item(cx, ty, LangItem::OwnedBox) && get_ty_param(ty).map_or(false, TyS::is_str))
+            || (match_type(cx, ty, &paths::COW) && get_ty_param(ty).map_or(false, TyS::is_str))
+        {
+            Some(RepeatKind::String)
+        } else {
+            let ty = ty.peel_refs();
+            (ty.is_str() || is_type_diagnostic_item(cx, ty, sym::string_type)).then(|| RepeatKind::String)
+        }
+    }
+}
+
+pub(super) fn check(
+    cx: &LateContext<'_>,
+    collect_expr: &Expr<'_>,
+    take_expr: &Expr<'_>,
+    take_self_arg: &Expr<'_>,
+    take_arg: &Expr<'_>,
+) {
+    if_chain! {
+        if let ExprKind::Call(repeat_fn, [repeat_arg]) = take_self_arg.kind;
+        if is_expr_path_def_path(cx, repeat_fn, &paths::ITER_REPEAT);
+        if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(collect_expr), sym::string_type);
+        if let Some(collect_id) = cx.typeck_results().type_dependent_def_id(collect_expr.hir_id);
+        if let Some(take_id) = cx.typeck_results().type_dependent_def_id(take_expr.hir_id);
+        if let Some(iter_trait_id) = cx.tcx.get_diagnostic_item(sym::Iterator);
+        if cx.tcx.trait_of_item(collect_id) == Some(iter_trait_id);
+        if cx.tcx.trait_of_item(take_id) == Some(iter_trait_id);
+        if let Some(repeat_kind) = parse_repeat_arg(cx, repeat_arg);
+        let ctxt = collect_expr.span.ctxt();
+        if ctxt == take_expr.span.ctxt();
+        if ctxt == take_self_arg.span.ctxt();
+        then {
+            let mut app = Applicability::MachineApplicable;
+            let count_snip = snippet_with_context(cx, take_arg.span, ctxt, "..", &mut app).0;
+
+            let val_str = match repeat_kind {
+                RepeatKind::Char(_) if repeat_arg.span.ctxt() != ctxt => return,
+                RepeatKind::Char('\'') => r#""'""#.into(),
+                RepeatKind::Char('"') => r#""\"""#.into(),
+                RepeatKind::Char(_) =>
+                    match snippet_with_applicability(cx, repeat_arg.span, "..", &mut app) {
+                        Cow::Owned(s) => Cow::Owned(format!("\"{}\"", &s[1..s.len() - 1])),
+                        s @ Cow::Borrowed(_) => s,
+                    },
+                RepeatKind::String =>
+                    Sugg::hir_with_context(cx, repeat_arg, ctxt, "..", &mut app).maybe_par().to_string().into(),
+            };
+
+            span_lint_and_sugg(
+                cx,
+                MANUAL_STR_REPEAT,
+                collect_expr.span,
+                "manual implementation of `str::repeat` using iterators",
+                "try this",
+                format!("{}.repeat({})", val_str, count_snip),
+                app
+            )
+        }
+    }
+}

clippy_lints/src/methods/mod.rs

@@ -32,6 +32,7 @@ mod iter_nth_zero;
 mod iter_skip_next;
 mod iterator_step_by_zero;
 mod manual_saturating_arithmetic;
+mod manual_str_repeat;
 mod map_collect_result_unit;
 mod map_flatten;
 mod map_unwrap_or;
@@ -62,7 +63,7 @@ mod zst_offset;
 use bind_instead_of_map::BindInsteadOfMap;
 use clippy_utils::diagnostics::{span_lint, span_lint_and_help};
 use clippy_utils::ty::{contains_adt_constructor, contains_ty, implements_trait, is_copy, is_type_diagnostic_item};
-use clippy_utils::{contains_return, get_trait_def_id, in_macro, iter_input_pats, paths, return_ty};
+use clippy_utils::{contains_return, get_trait_def_id, in_macro, iter_input_pats, meets_msrv, msrvs, paths, return_ty};
 use if_chain::if_chain;
 use rustc_hir as hir;
 use rustc_hir::def::Res;
@@ -1664,6 +1665,27 @@ declare_clippy_lint! {
     "checks for `.splitn(0, ..)` and `.splitn(1, ..)`"
 }
 
+declare_clippy_lint! {
+    /// **What it does:** Checks for manual implementations of `str::repeat`
+    ///
+    /// **Why is this bad?** These are both harder to read, as well as less performant.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    ///
+    /// ```rust
+    /// // Bad
+    /// let x: String = std::iter::repeat('x').take(10).collect();
+    ///
+    /// // Good
+    /// let x: String = "x".repeat(10);
+    /// ```
+    pub MANUAL_STR_REPEAT,
+    perf,
+    "manual implementation of `str::repeat`"
+}
+
 pub struct Methods {
     avoid_breaking_exported_api: bool,
     msrv: Option<RustcVersion>,
@@ -1737,7 +1759,8 @@ impl_lint_pass!(Methods => [
     FROM_ITER_INSTEAD_OF_COLLECT,
     INSPECT_FOR_EACH,
     IMPLICIT_CLONE,
-    SUSPICIOUS_SPLITN
+    SUSPICIOUS_SPLITN,
+    MANUAL_STR_REPEAT
 ]);
 
 /// Extracts a method call name, args, and `Span` of the method name.
@@ -1981,6 +2004,11 @@ fn check_methods<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, msrv: Optio
                 Some(("map", [m_recv, m_arg], _)) => {
                     map_collect_result_unit::check(cx, expr, m_recv, m_arg, recv);
                 },
+                Some(("take", [take_self_arg, take_arg], _)) => {
+                    if meets_msrv(msrv, &msrvs::STR_REPEAT) {
+                        manual_str_repeat::check(cx, expr, recv, take_self_arg, take_arg);
+                    }
+                },
                 _ => {},
             },
             ("count", []) => match method_call!(recv) {

clippy_lints/src/utils/conf.rs

@@ -124,7 +124,7 @@ macro_rules! define_Conf {
 define_Conf! {
     /// Lint: ENUM_VARIANT_NAMES, LARGE_TYPES_PASSED_BY_VALUE, TRIVIALLY_COPY_PASS_BY_REF, UNNECESSARY_WRAPS, UPPER_CASE_ACRONYMS, WRONG_SELF_CONVENTION. Suppress lints whenever the suggested change would cause breakage for other crates.
     (avoid_breaking_exported_api: bool = true),
-    /// Lint: CLONED_INSTEAD_OF_COPIED, REDUNDANT_FIELD_NAMES, REDUNDANT_STATIC_LIFETIMES, FILTER_MAP_NEXT, CHECKED_CONVERSIONS, MANUAL_RANGE_CONTAINS, USE_SELF, MEM_REPLACE_WITH_DEFAULT, MANUAL_NON_EXHAUSTIVE, OPTION_AS_REF_DEREF, MAP_UNWRAP_OR, MATCH_LIKE_MATCHES_MACRO, MANUAL_STRIP, MISSING_CONST_FOR_FN, UNNESTED_OR_PATTERNS, FROM_OVER_INTO, PTR_AS_PTR, IF_THEN_SOME_ELSE_NONE. The minimum rust version that the project supports
+    /// Lint: MANUAL_STR_REPEAT, CLONED_INSTEAD_OF_COPIED, REDUNDANT_FIELD_NAMES, REDUNDANT_STATIC_LIFETIMES, FILTER_MAP_NEXT, CHECKED_CONVERSIONS, MANUAL_RANGE_CONTAINS, USE_SELF, MEM_REPLACE_WITH_DEFAULT, MANUAL_NON_EXHAUSTIVE, OPTION_AS_REF_DEREF, MAP_UNWRAP_OR, MATCH_LIKE_MATCHES_MACRO, MANUAL_STRIP, MISSING_CONST_FOR_FN, UNNESTED_OR_PATTERNS, FROM_OVER_INTO, PTR_AS_PTR, IF_THEN_SOME_ELSE_NONE. The minimum rust version that the project supports
     (msrv: Option<String> = None),
     /// Lint: BLACKLISTED_NAME. The list of blacklisted names to lint about. NB: `bar` is not here since it has legitimate uses
     (blacklisted_names: Vec<String> = ["foo", "baz", "quux"].iter().map(ToString::to_string).collect()),

clippy_utils/src/msrvs.rs

@@ -26,4 +26,5 @@ msrv_aliases! {
     1,34,0 { TRY_FROM }
     1,30,0 { ITERATOR_FIND_MAP }
     1,17,0 { FIELD_INIT_SHORTHAND, STATIC_IN_CONST }
+    1,16,0 { STR_REPEAT }
 }

clippy_utils/src/sugg.rs

@@ -2,15 +2,15 @@
 #![deny(clippy::missing_docs_in_private_items)]
 
 use crate::higher;
-use crate::source::{snippet, snippet_opt, snippet_with_macro_callsite};
+use crate::source::{snippet, snippet_opt, snippet_with_context, snippet_with_macro_callsite};
 use rustc_ast::util::parser::AssocOp;
 use rustc_ast::{ast, token};
 use rustc_ast_pretty::pprust::token_kind_to_string;
 use rustc_errors::Applicability;
 use rustc_hir as hir;
 use rustc_lint::{EarlyContext, LateContext, LintContext};
 use rustc_span::source_map::{CharPos, Span};
-use rustc_span::{BytePos, Pos};
+use rustc_span::{BytePos, Pos, SyntaxContext};
 use std::borrow::Cow;
 use std::convert::TryInto;
 use std::fmt::Display;
@@ -90,6 +90,29 @@ impl<'a> Sugg<'a> {
         Self::hir_from_snippet(expr, snippet)
     }
 
+    /// Same as `hir`, but first walks the span up to the given context. This will result in the
+    /// macro call, rather then the expansion, if the span is from a child context. If the span is
+    /// not from a child context, it will be used directly instead.
+    ///
+    /// e.g. Given the expression `&vec![]`, getting a snippet from the span for `vec![]` as a HIR
+    /// node would result in `box []`. If given the context of the address of expression, this
+    /// function will correctly get a snippet of `vec![]`.
+    pub fn hir_with_context(
+        cx: &LateContext<'_>,
+        expr: &hir::Expr<'_>,
+        ctxt: SyntaxContext,
+        default: &'a str,
+        applicability: &mut Applicability,
+    ) -> Self {
+        let (snippet, in_macro) = snippet_with_context(cx, expr.span, ctxt, default, applicability);
+
+        if in_macro {
+            Sugg::NonParen(snippet)
+        } else {
+            Self::hir_from_snippet(expr, snippet)
+        }
+    }
+
     /// Generate a suggestion for an expression with the given snippet. This is used by the `hir_*`
     /// function variants of `Sugg`, since these use different snippet functions.
     fn hir_from_snippet(expr: &hir::Expr<'_>, snippet: Cow<'a, str>) -> Self {

tests/ui/manual_str_repeat.fixed

@@ -0,0 +1,66 @@
+// run-rustfix
+
+#![feature(custom_inner_attributes)]
+#![warn(clippy::manual_str_repeat)]
+
+use std::borrow::Cow;
+use std::iter::{repeat, FromIterator};
+
+fn main() {
+    let _: String = "test".repeat(10);
+    let _: String = "x".repeat(10);
+    let _: String = "'".repeat(10);
+    let _: String = "\"".repeat(10);
+
+    let x = "test";
+    let count = 10;
+    let _ = x.repeat(count + 2);
+
+    macro_rules! m {
+        ($e:expr) => {{ $e }};
+    }
+    // FIXME: macro args are fine
+    let _: String = repeat(m!("test")).take(m!(count)).collect();
+
+    let x = &x;
+    let _: String = (*x).repeat(count);
+
+    macro_rules! repeat_m {
+        ($e:expr) => {{ repeat($e) }};
+    }
+    // Don't lint, repeat is from a macro.
+    let _: String = repeat_m!("test").take(count).collect();
+
+    let x: Box<str> = Box::from("test");
+    let _: String = x.repeat(count);
+
+    #[derive(Clone)]
+    struct S;
+    impl FromIterator<Box<S>> for String {
+        fn from_iter<T: IntoIterator<Item = Box<S>>>(_: T) -> Self {
+            Self::new()
+        }
+    }
+    // Don't lint, wrong box type
+    let _: String = repeat(Box::new(S)).take(count).collect();
+
+    let _: String = Cow::Borrowed("test").repeat(count);
+
+    let x = "x".to_owned();
+    let _: String = x.repeat(count);
+
+    let x = 'x';
+    // Don't lint, not char literal
+    let _: String = repeat(x).take(count).collect();
+}
+
+fn _msrv_1_15() {
+    #![clippy::msrv = "1.15"]
+    // `str::repeat` was stabilized in 1.16. Do not lint this
+    let _: String = std::iter::repeat("test").take(10).collect();
+}
+
+fn _msrv_1_16() {
+    #![clippy::msrv = "1.16"]
+    let _: String = "test".repeat(10);
+}