Update upstream source from tag 'upstream/1.52.1+dfsg1'

[rustc.git] / src / tools / clippy / clippy_lints / src / repeat_once.rs

diff --git a/src/tools/clippy/clippy_lints/src/repeat_once.rs b/src/tools/clippy/clippy_lints/src/repeat_once.rs
new file mode 100644 (file)
index 0000000..d34e744
--- /dev/null
+++ b/src/tools/clippy/clippy_lints/src/repeat_once.rs
@@ -0,0 +1,83 @@
+use crate::consts::{constant_context, Constant};
+use crate::utils::{in_macro, is_type_diagnostic_item, snippet, span_lint_and_sugg};
+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::sym;
+
+declare_clippy_lint! {
+    /// **What it does:** Checks for usage of `.repeat(1)` and suggest the following method for each types.
+    /// - `.to_string()` for `str`
+    /// - `.clone()` for `String`
+    /// - `.to_vec()` for `slice`
+    ///
+    /// **Why is this bad?** For example, `String.repeat(1)` is equivalent to `.clone()`. If cloning the string is the intention behind this, `clone()` should be used.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    ///
+    /// ```rust
+    /// fn main() {
+    ///     let x = String::from("hello world").repeat(1);
+    /// }
+    /// ```
+    /// Use instead:
+    /// ```rust
+    /// fn main() {
+    ///     let x = String::from("hello world").clone();
+    /// }
+    /// ```
+    pub REPEAT_ONCE,
+    complexity,
+    "using `.repeat(1)` instead of `String.clone()`, `str.to_string()` or `slice.to_vec()` "
+}
+
+declare_lint_pass!(RepeatOnce => [REPEAT_ONCE]);
+
+impl<'tcx> LateLintPass<'tcx> for RepeatOnce {
+    fn check_expr(&mut self, cx: &LateContext<'_>, expr: &'tcx Expr<'_>) {
+        if_chain! {
+            if let ExprKind::MethodCall(path, _, [receiver, count], _) = &expr.kind;
+            if path.ident.name == sym!(repeat);
+            if let Some(Constant::Int(1)) = constant_context(cx, cx.typeck_results()).expr(&count);
+            if !in_macro(receiver.span);
+            then {
+                let ty = cx.typeck_results().expr_ty(&receiver).peel_refs();
+                if ty.is_str() {
+                    span_lint_and_sugg(
+                        cx,
+                        REPEAT_ONCE,
+                        expr.span,
+                        "calling `repeat(1)` on str",
+                        "consider using `.to_string()` instead",
+                        format!("{}.to_string()", snippet(cx, receiver.span, r#""...""#)),
+                        Applicability::MachineApplicable,
+                    );
+                } else if ty.builtin_index().is_some() {
+                    span_lint_and_sugg(
+                        cx,
+                        REPEAT_ONCE,
+                        expr.span,
+                        "calling `repeat(1)` on slice",
+                        "consider using `.to_vec()` instead",
+                        format!("{}.to_vec()", snippet(cx, receiver.span, r#""...""#)),
+                        Applicability::MachineApplicable,
+                    );
+                } else if is_type_diagnostic_item(cx, ty, sym::string_type) {
+                    span_lint_and_sugg(
+                        cx,
+                        REPEAT_ONCE,
+                        expr.span,
+                        "calling `repeat(1)` on a string literal",
+                        "consider using `.clone()` instead",
+                        format!("{}.clone()", snippet(cx, receiver.span, r#""...""#)),
+                        Applicability::MachineApplicable,
+                    );
+                }
+            }
+        }
+    }
+}