1 files changed, 99 insertions, 0 deletions
diff --git a/src/tools/clippy/clippy_lints/src/to_digit_is_some.rs b/src/tools/clippy/clippy_lints/src/to_digit_is_some.rs
new file mode 100644
index 000000000..aa6c01b3a
--- /dev/null
+++ b/src/tools/clippy/clippy_lints/src/to_digit_is_some.rs
@@ -0,0 +1,99 @@
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::match_def_path;
+use clippy_utils::source::snippet_with_applicability;
+use if_chain::if_chain;
+use rustc_errors::Applicability;
+use rustc_hir as hir;
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_middle::ty;
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for `.to_digit(..).is_some()` on `char`s.
+    ///
+    /// ### Why is this bad?
+    /// This is a convoluted way of checking if a `char` is a digit. It's
+    /// more straight forward to use the dedicated `is_digit` method.
+    ///
+    /// ### Example
+    /// ```rust
+    /// # let c = 'c';
+    /// # let radix = 10;
+    /// let is_digit = c.to_digit(radix).is_some();
+    /// ```
+    /// can be written as:
+    /// ```
+    /// # let c = 'c';
+    /// # let radix = 10;
+    /// let is_digit = c.is_digit(radix);
+    /// ```
+    #[clippy::version = "1.41.0"]
+    pub TO_DIGIT_IS_SOME,
+    style,
+    "`char.is_digit()` is clearer"
+}
+
+declare_lint_pass!(ToDigitIsSome => [TO_DIGIT_IS_SOME]);
+
+impl<'tcx> LateLintPass<'tcx> for ToDigitIsSome {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
+        if_chain! {
+            if let hir::ExprKind::MethodCall(is_some_path, is_some_args, _) = &expr.kind;
+            if is_some_path.ident.name.as_str() == "is_some";
+            if let [to_digit_expr] = &**is_some_args;
+            then {
+                let match_result = match &to_digit_expr.kind {
+                    hir::ExprKind::MethodCall(to_digits_path, to_digit_args, _) => {
+                        if_chain! {
+                            if let [char_arg, radix_arg] = &**to_digit_args;
+                            if to_digits_path.ident.name.as_str() == "to_digit";
+                            let char_arg_ty = cx.typeck_results().expr_ty_adjusted(char_arg);
+                            if *char_arg_ty.kind() == ty::Char;
+                            then {
+                                Some((true, char_arg, radix_arg))
+                            } else {
+                                None
+                            }
+                        }
+                    }
+                    hir::ExprKind::Call(to_digits_call, to_digit_args) => {
+                        if_chain! {
+                            if let [char_arg, radix_arg] = &**to_digit_args;
+                            if let hir::ExprKind::Path(to_digits_path) = &to_digits_call.kind;
+                            if let to_digits_call_res = cx.qpath_res(to_digits_path, to_digits_call.hir_id);
+                            if let Some(to_digits_def_id) = to_digits_call_res.opt_def_id();
+                            if match_def_path(cx, to_digits_def_id, &["core", "char", "methods", "<impl char>", "to_digit"]);
+                            then {
+                                Some((false, char_arg, radix_arg))
+                            } else {
+                                None
+                            }
+                        }
+                    }
+                    _ => None
+                };
+
+                if let Some((is_method_call, char_arg, radix_arg)) = match_result {
+                    let mut applicability = Applicability::MachineApplicable;
+                    let char_arg_snip = snippet_with_applicability(cx, char_arg.span, "_", &mut applicability);
+                    let radix_snip = snippet_with_applicability(cx, radix_arg.span, "_", &mut applicability);
+
+                    span_lint_and_sugg(
+                        cx,
+                        TO_DIGIT_IS_SOME,
+                        expr.span,
+                        "use of `.to_digit(..).is_some()`",
+                        "try this",
+                        if is_method_call {
+                            format!("{}.is_digit({})", char_arg_snip, radix_snip)
+                        } else {
+                            format!("char::is_digit({}, {})", char_arg_snip, radix_snip)
+                        },
+                        applicability,
+                    );
+                }
+            }
+        }
+    }
+}