Add lint to check manual pattern char comparison and merge its code with single_char_pattern lint

18 files changed, 451 insertions, 163 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 711b7fb7914..d7bcd7a1968 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5532,6 +5532,7 @@ Released 2018-09-13
 [`manual_next_back`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_next_back
 [`manual_non_exhaustive`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_non_exhaustive
 [`manual_ok_or`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_ok_or
+[`manual_pattern_char_comparison`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_pattern_char_comparison
 [`manual_range_contains`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_range_contains
 [`manual_range_patterns`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_range_patterns
 [`manual_rem_euclid`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_rem_euclid
diff --git a/clippy_lints/src/declared_lints.rs b/clippy_lints/src/declared_lints.rs
index a9f2dd4499a..7e43a99e9f2 100644
--- a/clippy_lints/src/declared_lints.rs
+++ b/clippy_lints/src/declared_lints.rs
@@ -448,7 +448,6 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::methods::SEEK_TO_START_INSTEAD_OF_REWIND_INFO,
     crate::methods::SHOULD_IMPLEMENT_TRAIT_INFO,
     crate::methods::SINGLE_CHAR_ADD_STR_INFO,
-    crate::methods::SINGLE_CHAR_PATTERN_INFO,
     crate::methods::SKIP_WHILE_NEXT_INFO,
     crate::methods::STABLE_SORT_PRIMITIVE_INFO,
     crate::methods::STRING_EXTEND_CHARS_INFO,
@@ -656,6 +655,8 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::std_instead_of_core::ALLOC_INSTEAD_OF_CORE_INFO,
     crate::std_instead_of_core::STD_INSTEAD_OF_ALLOC_INFO,
     crate::std_instead_of_core::STD_INSTEAD_OF_CORE_INFO,
+    crate::string_patterns::MANUAL_PATTERN_CHAR_COMPARISON_INFO,
+    crate::string_patterns::SINGLE_CHAR_PATTERN_INFO,
     crate::strings::STRING_ADD_INFO,
     crate::strings::STRING_ADD_ASSIGN_INFO,
     crate::strings::STRING_FROM_UTF8_AS_BYTES_INFO,
diff --git a/clippy_lints/src/float_literal.rs b/clippy_lints/src/float_literal.rs
index 4ec9bd757ff..4d301daabe4 100644
--- a/clippy_lints/src/float_literal.rs
+++ b/clippy_lints/src/float_literal.rs
@@ -103,7 +103,7 @@ impl<'tcx> LateLintPass<'tcx> for FloatLiteral {
                 return;
             }
 
-            if is_whole && !sym_str.contains(|c| c == 'e' || c == 'E') {
+            if is_whole && !sym_str.contains(['e', 'E']) {
                 // Normalize the literal by stripping the fractional portion
                 if sym_str.split('.').next().unwrap() != float_str {
                     // If the type suffix is missing the suggestion would be
diff --git a/clippy_lints/src/lib.rs b/clippy_lints/src/lib.rs
index 6946c2986f4..c65581d5203 100644
--- a/clippy_lints/src/lib.rs
+++ b/clippy_lints/src/lib.rs
@@ -326,6 +326,7 @@ mod size_of_in_element_count;
 mod size_of_ref;
 mod slow_vector_initialization;
 mod std_instead_of_core;
+mod string_patterns;
 mod strings;
 mod strlen_on_c_strings;
 mod suspicious_operation_groupings;
@@ -1167,6 +1168,7 @@ pub fn register_lints(store: &mut rustc_lint::LintStore, conf: &'static Conf) {
             ..Default::default()
         })
     });
+    store.register_late_pass(|_| Box::new(string_patterns::StringPatterns));
     // add lints here, do not remove this comment, it's used in `new_lint`
 }
 
diff --git a/clippy_lints/src/methods/mod.rs b/clippy_lints/src/methods/mod.rs
index c3699d6341a..6200716afbe 100644
--- a/clippy_lints/src/methods/mod.rs
+++ b/clippy_lints/src/methods/mod.rs
@@ -94,7 +94,6 @@ mod seek_from_current;
 mod seek_to_start_instead_of_rewind;
 mod single_char_add_str;
 mod single_char_insert_string;
-mod single_char_pattern;
 mod single_char_push_string;
 mod skip_while_next;
 mod stable_sort_primitive;
@@ -1143,38 +1142,6 @@ declare_clippy_lint! {
 
 declare_clippy_lint! {
     /// ### What it does
-    /// Checks for string methods that receive a single-character
-    /// `str` as an argument, e.g., `_.split("x")`.
-    ///
-    /// ### Why is this bad?
-    /// While this can make a perf difference on some systems,
-    /// benchmarks have proven inconclusive. But at least using a
-    /// char literal makes it clear that we are looking at a single
-    /// character.
-    ///
-    /// ### Known problems
-    /// Does not catch multi-byte unicode characters. This is by
-    /// design, on many machines, splitting by a non-ascii char is
-    /// actually slower. Please do your own measurements instead of
-    /// relying solely on the results of this lint.
-    ///
-    /// ### Example
-    /// ```rust,ignore
-    /// _.split("x");
-    /// ```
-    ///
-    /// Use instead:
-    /// ```rust,ignore
-    /// _.split('x');
-    /// ```
-    #[clippy::version = "pre 1.29.0"]
-    pub SINGLE_CHAR_PATTERN,
-    pedantic,
-    "using a single-character str where a char could be used, e.g., `_.split(\"x\")`"
-}
-
-declare_clippy_lint! {
-    /// ### What it does
     /// Checks for calling `.step_by(0)` on iterators which panics.
     ///
     /// ### Why is this bad?
@@ -4169,7 +4136,6 @@ impl_lint_pass!(Methods => [
     FLAT_MAP_OPTION,
     INEFFICIENT_TO_STRING,
     NEW_RET_NO_SELF,
-    SINGLE_CHAR_PATTERN,
     SINGLE_CHAR_ADD_STR,
     SEARCH_IS_SOME,
     FILTER_NEXT,
@@ -4324,7 +4290,6 @@ impl<'tcx> LateLintPass<'tcx> for Methods {
                 inefficient_to_string::check(cx, expr, method_call.ident.name, receiver, args);
                 single_char_add_str::check(cx, expr, receiver, args);
                 into_iter_on_ref::check(cx, expr, method_span, method_call.ident.name, receiver);
-                single_char_pattern::check(cx, expr, method_call.ident.name, receiver, args);
                 unnecessary_to_owned::check(cx, expr, method_call.ident.name, receiver, args, &self.msrv);
             },
             ExprKind::Binary(op, lhs, rhs) if op.node == hir::BinOpKind::Eq || op.node == hir::BinOpKind::Ne => {
diff --git a/clippy_lints/src/methods/path_buf_push_overwrite.rs b/clippy_lints/src/methods/path_buf_push_overwrite.rs
index 04a27cc98f3..2d3007e50b8 100644
--- a/clippy_lints/src/methods/path_buf_push_overwrite.rs
+++ b/clippy_lints/src/methods/path_buf_push_overwrite.rs
@@ -27,7 +27,7 @@ pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, arg: &'t
             lit.span,
             "calling `push` with '/' or '\\' (file system root) will overwrite the previous path definition",
             "try",
-            format!("\"{}\"", pushed_path_lit.trim_start_matches(|c| c == '/' || c == '\\')),
+            format!("\"{}\"", pushed_path_lit.trim_start_matches(['/', '\\'])),
             Applicability::MachineApplicable,
         );
     }
diff --git a/clippy_lints/src/methods/single_char_insert_string.rs b/clippy_lints/src/methods/single_char_insert_string.rs
index ba9ef9c84f9..e2f76ac114c 100644
--- a/clippy_lints/src/methods/single_char_insert_string.rs
+++ b/clippy_lints/src/methods/single_char_insert_string.rs
@@ -1,6 +1,5 @@
-use super::utils::get_hint_if_single_char_arg;
 use clippy_utils::diagnostics::span_lint_and_sugg;
-use clippy_utils::source::snippet_with_applicability;
+use clippy_utils::source::{snippet_with_applicability, str_literal_to_char_literal};
 use rustc_ast::BorrowKind;
 use rustc_errors::Applicability;
 use rustc_hir::{self as hir, ExprKind};
@@ -11,7 +10,7 @@ use super::SINGLE_CHAR_ADD_STR;
 /// lint for length-1 `str`s as argument for `insert_str`
 pub(super) fn check(cx: &LateContext<'_>, expr: &hir::Expr<'_>, receiver: &hir::Expr<'_>, args: &[hir::Expr<'_>]) {
     let mut applicability = Applicability::MachineApplicable;
-    if let Some(extension_string) = get_hint_if_single_char_arg(cx, &args[1], &mut applicability, false) {
+    if let Some(extension_string) = str_literal_to_char_literal(cx, &args[1], &mut applicability, false) {
         let base_string_snippet =
             snippet_with_applicability(cx, receiver.span.source_callsite(), "_", &mut applicability);
         let pos_arg = snippet_with_applicability(cx, args[0].span, "..", &mut applicability);
diff --git a/clippy_lints/src/methods/single_char_pattern.rs b/clippy_lints/src/methods/single_char_pattern.rs
deleted file mode 100644
index 982a7901c45..00000000000
--- a/clippy_lints/src/methods/single_char_pattern.rs
+++ /dev/null
@@ -1,64 +0,0 @@
-use super::utils::get_hint_if_single_char_arg;
-use clippy_utils::diagnostics::span_lint_and_sugg;
-use rustc_errors::Applicability;
-use rustc_hir as hir;
-use rustc_lint::LateContext;
-use rustc_middle::ty;
-use rustc_span::symbol::Symbol;
-
-use super::SINGLE_CHAR_PATTERN;
-
-const PATTERN_METHODS: [(&str, usize); 22] = [
-    ("contains", 0),
-    ("starts_with", 0),
-    ("ends_with", 0),
-    ("find", 0),
-    ("rfind", 0),
-    ("split", 0),
-    ("split_inclusive", 0),
-    ("rsplit", 0),
-    ("split_terminator", 0),
-    ("rsplit_terminator", 0),
-    ("splitn", 1),
-    ("rsplitn", 1),
-    ("split_once", 0),
-    ("rsplit_once", 0),
-    ("matches", 0),
-    ("rmatches", 0),
-    ("match_indices", 0),
-    ("rmatch_indices", 0),
-    ("trim_start_matches", 0),
-    ("trim_end_matches", 0),
-    ("replace", 0),
-    ("replacen", 0),
-];
-
-/// lint for length-1 `str`s for methods in `PATTERN_METHODS`
-pub(super) fn check(
-    cx: &LateContext<'_>,
-    _expr: &hir::Expr<'_>,
-    method_name: Symbol,
-    receiver: &hir::Expr<'_>,
-    args: &[hir::Expr<'_>],
-) {
-    for &(method, pos) in &PATTERN_METHODS {
-        if let ty::Ref(_, ty, _) = cx.typeck_results().expr_ty_adjusted(receiver).kind()
-            && ty.is_str()
-            && method_name.as_str() == method
-            && args.len() > pos
-            && let arg = &args[pos]
-            && let mut applicability = Applicability::MachineApplicable
-            && let Some(hint) = get_hint_if_single_char_arg(cx, arg, &mut applicability, true)
-        {
-            span_lint_and_sugg(
-                cx,
-                SINGLE_CHAR_PATTERN,
-                arg.span,
-                "single-character string constant used as pattern",
-                "consider using a `char`",
-                hint,
-                applicability,
-            );
-        }
-    }
-}
diff --git a/clippy_lints/src/methods/single_char_push_string.rs b/clippy_lints/src/methods/single_char_push_string.rs
index f00a5ab455e..4ae8634305d 100644
--- a/clippy_lints/src/methods/single_char_push_string.rs
+++ b/clippy_lints/src/methods/single_char_push_string.rs
@@ -1,6 +1,5 @@
-use super::utils::get_hint_if_single_char_arg;
 use clippy_utils::diagnostics::span_lint_and_sugg;
-use clippy_utils::source::snippet_with_applicability;
+use clippy_utils::source::{snippet_with_applicability, str_literal_to_char_literal};
 use rustc_ast::BorrowKind;
 use rustc_errors::Applicability;
 use rustc_hir::{self as hir, ExprKind};
@@ -11,7 +10,7 @@ use super::SINGLE_CHAR_ADD_STR;
 /// lint for length-1 `str`s as argument for `push_str`
 pub(super) fn check(cx: &LateContext<'_>, expr: &hir::Expr<'_>, receiver: &hir::Expr<'_>, args: &[hir::Expr<'_>]) {
     let mut applicability = Applicability::MachineApplicable;
-    if let Some(extension_string) = get_hint_if_single_char_arg(cx, &args[0], &mut applicability, false) {
+    if let Some(extension_string) = str_literal_to_char_literal(cx, &args[0], &mut applicability, false) {
         let base_string_snippet =
             snippet_with_applicability(cx, receiver.span.source_callsite(), "..", &mut applicability);
         let sugg = format!("{base_string_snippet}.push({extension_string})");
diff --git a/clippy_lints/src/methods/utils.rs b/clippy_lints/src/methods/utils.rs
index 5d58c73f8b2..0d2b0a31317 100644
--- a/clippy_lints/src/methods/utils.rs
+++ b/clippy_lints/src/methods/utils.rs
@@ -1,8 +1,5 @@
-use clippy_utils::source::snippet_with_applicability;
 use clippy_utils::ty::is_type_diagnostic_item;
 use clippy_utils::{get_parent_expr, path_to_local_id, usage};
-use rustc_ast::ast;
-use rustc_errors::Applicability;
 use rustc_hir::intravisit::{walk_expr, Visitor};
 use rustc_hir::{BorrowKind, Expr, ExprKind, HirId, Mutability, Pat, QPath, Stmt, StmtKind};
 use rustc_lint::LateContext;
@@ -49,48 +46,6 @@ pub(super) fn derefs_to_slice<'tcx>(
     }
 }
 
-pub(super) fn get_hint_if_single_char_arg(
-    cx: &LateContext<'_>,
-    arg: &Expr<'_>,
-    applicability: &mut Applicability,
-    ascii_only: bool,
-) -> Option<String> {
-    if let ExprKind::Lit(lit) = &arg.kind
-        && let ast::LitKind::Str(r, style) = lit.node
-        && let string = r.as_str()
-        && let len = if ascii_only {
-            string.len()
-        } else {
-            string.chars().count()
-        }
-        && len == 1
-    {
-        let snip = snippet_with_applicability(cx, arg.span, string, applicability);
-        let ch = if let ast::StrStyle::Raw(nhash) = style {
-            let nhash = nhash as usize;
-            // for raw string: r##"a"##
-            &snip[(nhash + 2)..(snip.len() - 1 - nhash)]
-        } else {
-            // for regular string: "a"
-            &snip[1..(snip.len() - 1)]
-        };
-
-        let hint = format!(
-            "'{}'",
-            match ch {
-                "'" => "\\'",
-                r"\" => "\\\\",
-                "\\\"" => "\"", // no need to escape `"` in `'"'`
-                _ => ch,
-            }
-        );
-
-        Some(hint)
-    } else {
-        None
-    }
-}
-
 /// The core logic of `check_for_loop_iter` in `unnecessary_iter_cloned.rs`, this function wraps a
 /// use of `CloneOrCopyVisitor`.
 pub(super) fn clone_or_copy_needed<'tcx>(
diff --git a/clippy_lints/src/misc_early/zero_prefixed_literal.rs b/clippy_lints/src/misc_early/zero_prefixed_literal.rs
index 4f9578d1b25..61f4684c9e3 100644
--- a/clippy_lints/src/misc_early/zero_prefixed_literal.rs
+++ b/clippy_lints/src/misc_early/zero_prefixed_literal.rs
@@ -6,7 +6,7 @@ use rustc_span::Span;
 use super::ZERO_PREFIXED_LITERAL;
 
 pub(super) fn check(cx: &EarlyContext<'_>, lit_span: Span, lit_snip: &str) {
-    let trimmed_lit_snip = lit_snip.trim_start_matches(|c| c == '_' || c == '0');
+    let trimmed_lit_snip = lit_snip.trim_start_matches(['_', '0']);
     span_lint_and_then(
         cx,
         ZERO_PREFIXED_LITERAL,
@@ -20,7 +20,7 @@ pub(super) fn check(cx: &EarlyContext<'_>, lit_span: Span, lit_snip: &str) {
                 Applicability::MaybeIncorrect,
             );
             // do not advise to use octal form if the literal cannot be expressed in base 8.
-            if !lit_snip.contains(|c| c == '8' || c == '9') {
+            if !lit_snip.contains(['8', '9']) {
                 diag.span_suggestion(
                     lit_span,
                     "if you mean to use an octal constant, use `0o`",
diff --git a/clippy_lints/src/string_patterns.rs b/clippy_lints/src/string_patterns.rs
new file mode 100644
index 00000000000..64b5b8f9f27
--- /dev/null
+++ b/clippy_lints/src/string_patterns.rs
@@ -0,0 +1,227 @@
+use std::ops::ControlFlow;
+
+use clippy_utils::diagnostics::{span_lint_and_sugg, span_lint_and_then};
+use clippy_utils::eager_or_lazy::switch_to_eager_eval;
+use clippy_utils::macros::matching_root_macro_call;
+use clippy_utils::path_to_local_id;
+use clippy_utils::source::{snippet, str_literal_to_char_literal};
+use clippy_utils::visitors::{for_each_expr, Descend};
+use itertools::Itertools;
+use rustc_ast::{BinOpKind, LitKind};
+use rustc_errors::Applicability;
+use rustc_hir::{Expr, ExprKind, PatKind};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_middle::ty;
+use rustc_session::declare_lint_pass;
+use rustc_span::{sym, Span};
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for manual `char` comparison in string patterns
+    ///
+    /// ### Why is this bad?
+    /// This can be written more concisely using a `char` or an array of `char`.
+    /// This is more readable and more optimized when comparing to only one `char`.
+    ///
+    /// ### Example
+    /// ```no_run
+    /// "Hello World!".trim_end_matches(|c| c == '.' || c == ',' || c == '!' || c == '?');
+    /// ```
+    /// Use instead:
+    /// ```no_run
+    /// "Hello World!".trim_end_matches(['.', ',', '!', '?']);
+    /// ```
+    #[clippy::version = "1.80.0"]
+    pub MANUAL_PATTERN_CHAR_COMPARISON,
+    style,
+    "manual char comparison in string patterns"
+}
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for string methods that receive a single-character
+    /// `str` as an argument, e.g., `_.split("x")`.
+    ///
+    /// ### Why is this bad?
+    /// While this can make a perf difference on some systems,
+    /// benchmarks have proven inconclusive. But at least using a
+    /// char literal makes it clear that we are looking at a single
+    /// character.
+    ///
+    /// ### Known problems
+    /// Does not catch multi-byte unicode characters. This is by
+    /// design, on many machines, splitting by a non-ascii char is
+    /// actually slower. Please do your own measurements instead of
+    /// relying solely on the results of this lint.
+    ///
+    /// ### Example
+    /// ```rust,ignore
+    /// _.split("x");
+    /// ```
+    ///
+    /// Use instead:
+    /// ```rust,ignore
+    /// _.split('x');
+    /// ```
+    #[clippy::version = "pre 1.29.0"]
+    pub SINGLE_CHAR_PATTERN,
+    pedantic,
+    "using a single-character str where a char could be used, e.g., `_.split(\"x\")`"
+}
+
+declare_lint_pass!(StringPatterns => [MANUAL_PATTERN_CHAR_COMPARISON, SINGLE_CHAR_PATTERN]);
+
+const PATTERN_METHODS: [(&str, usize); 22] = [
+    ("contains", 0),
+    ("starts_with", 0),
+    ("ends_with", 0),
+    ("find", 0),
+    ("rfind", 0),
+    ("split", 0),
+    ("split_inclusive", 0),
+    ("rsplit", 0),
+    ("split_terminator", 0),
+    ("rsplit_terminator", 0),
+    ("splitn", 1),
+    ("rsplitn", 1),
+    ("split_once", 0),
+    ("rsplit_once", 0),
+    ("matches", 0),
+    ("rmatches", 0),
+    ("match_indices", 0),
+    ("rmatch_indices", 0),
+    ("trim_start_matches", 0),
+    ("trim_end_matches", 0),
+    ("replace", 0),
+    ("replacen", 0),
+];
+
+fn check_single_char_pattern_lint(cx: &LateContext<'_>, arg: &Expr<'_>) {
+    let mut applicability = Applicability::MachineApplicable;
+    if let Some(hint) = str_literal_to_char_literal(cx, arg, &mut applicability, true) {
+        span_lint_and_sugg(
+            cx,
+            SINGLE_CHAR_PATTERN,
+            arg.span,
+            "single-character string constant used as pattern",
+            "consider using a `char`",
+            hint,
+            applicability,
+        );
+    }
+}
+
+fn get_char_span<'tcx>(cx: &'_ LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<Span> {
+    if cx.typeck_results().expr_ty_adjusted(expr).is_char()
+        && !expr.span.from_expansion()
+        && switch_to_eager_eval(cx, expr)
+    {
+        Some(expr.span)
+    } else {
+        None
+    }
+}
+
+fn check_manual_pattern_char_comparison(cx: &LateContext<'_>, method_arg: &Expr<'_>) {
+    if let ExprKind::Closure(closure) = method_arg.kind
+        && let body = cx.tcx.hir().body(closure.body)
+        && let Some(PatKind::Binding(_, binding, ..)) = body.params.first().map(|p| p.pat.kind)
+    {
+        let mut set_char_spans: Vec<Span> = Vec::new();
+
+        // We want to retrieve all the comparisons done.
+        // They are ordered in a nested way and so we need to traverse the AST to collect them all.
+        if for_each_expr(cx, body.value, |sub_expr| -> ControlFlow<(), Descend> {
+            match sub_expr.kind {
+                ExprKind::Binary(op, left, right) if op.node == BinOpKind::Eq => {
+                    if path_to_local_id(left, binding)
+                        && let Some(span) = get_char_span(cx, right)
+                    {
+                        set_char_spans.push(span);
+                        ControlFlow::Continue(Descend::No)
+                    } else if path_to_local_id(right, binding)
+                        && let Some(span) = get_char_span(cx, left)
+                    {
+                        set_char_spans.push(span);
+                        ControlFlow::Continue(Descend::No)
+                    } else {
+                        ControlFlow::Break(())
+                    }
+                },
+                ExprKind::Binary(op, _, _) if op.node == BinOpKind::Or => ControlFlow::Continue(Descend::Yes),
+                ExprKind::Match(match_value, [arm, _], _) => {
+                    if matching_root_macro_call(cx, sub_expr.span, sym::matches_macro).is_none()
+                        || arm.guard.is_some()
+                        || !path_to_local_id(match_value, binding)
+                    {
+                        return ControlFlow::Break(());
+                    }
+                    if arm.pat.walk_short(|pat| match pat.kind {
+                        PatKind::Lit(expr) if let ExprKind::Lit(lit) = expr.kind => {
+                            if let LitKind::Char(_) = lit.node {
+                                set_char_spans.push(lit.span);
+                            }
+                            true
+                        },
+                        PatKind::Or(_) => true,
+                        _ => false,
+                    }) {
+                        ControlFlow::Continue(Descend::No)
+                    } else {
+                        ControlFlow::Break(())
+                    }
+                },
+                _ => ControlFlow::Break(()),
+            }
+        })
+        .is_some()
+        {
+            return;
+        }
+        span_lint_and_then(
+            cx,
+            MANUAL_PATTERN_CHAR_COMPARISON,
+            method_arg.span,
+            "this manual char comparison can be written more succinctly",
+            |diag| {
+                if let [set_char_span] = set_char_spans[..] {
+                    diag.span_suggestion(
+                        method_arg.span,
+                        "consider using a `char`",
+                        snippet(cx, set_char_span, "c"),
+                        Applicability::MachineApplicable,
+                    );
+                } else {
+                    diag.span_suggestion(
+                        method_arg.span,
+                        "consider using an array of `char`",
+                        format!(
+                            "[{}]",
+                            set_char_spans.into_iter().map(|span| snippet(cx, span, "c")).join(", ")
+                        ),
+                        Applicability::MachineApplicable,
+                    );
+                }
+            },
+        );
+    }
+}
+
+impl<'tcx> LateLintPass<'tcx> for StringPatterns {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
+        if !expr.span.from_expansion()
+            && let ExprKind::MethodCall(method, receiver, args, _) = expr.kind
+            && let ty::Ref(_, ty, _) = cx.typeck_results().expr_ty_adjusted(receiver).kind()
+            && ty.is_str()
+            && let method_name = method.ident.name.as_str()
+            && let Some(&(_, pos)) = PATTERN_METHODS
+                .iter()
+                .find(|(array_method_name, _)| *array_method_name == method_name)
+            && let Some(arg) = args.get(pos)
+        {
+            check_single_char_pattern_lint(cx, arg);
+
+            check_manual_pattern_char_comparison(cx, arg);
+        }
+    }
+}
diff --git a/clippy_utils/src/source.rs b/clippy_utils/src/source.rs
index 69f593fe04a..b7ff7ebe910 100644
--- a/clippy_utils/src/source.rs
+++ b/clippy_utils/src/source.rs
@@ -2,6 +2,7 @@
 
 #![allow(clippy::module_name_repetitions)]
 
+use rustc_ast::{LitKind, StrStyle};
 use rustc_data_structures::sync::Lrc;
 use rustc_errors::Applicability;
 use rustc_hir::{BlockCheckMode, Expr, ExprKind, UnsafeSource};
@@ -500,6 +501,50 @@ pub fn expand_past_previous_comma(cx: &LateContext<'_>, span: Span) -> Span {
     extended.with_lo(extended.lo() - BytePos(1))
 }
 
+/// Converts `expr` to a `char` literal if it's a `str` literal containing a single
+/// character (or a single byte with `ascii_only`)
+pub fn str_literal_to_char_literal(
+    cx: &LateContext<'_>,
+    expr: &Expr<'_>,
+    applicability: &mut Applicability,
+    ascii_only: bool,
+) -> Option<String> {
+    if let ExprKind::Lit(lit) = &expr.kind
+        && let LitKind::Str(r, style) = lit.node
+        && let string = r.as_str()
+        && let len = if ascii_only {
+            string.len()
+        } else {
+            string.chars().count()
+        }
+        && len == 1
+    {
+        let snip = snippet_with_applicability(cx, expr.span, string, applicability);
+        let ch = if let StrStyle::Raw(nhash) = style {
+            let nhash = nhash as usize;
+            // for raw string: r##"a"##
+            &snip[(nhash + 2)..(snip.len() - 1 - nhash)]
+        } else {
+            // for regular string: "a"
+            &snip[1..(snip.len() - 1)]
+        };
+
+        let hint = format!(
+            "'{}'",
+            match ch {
+                "'" => "\\'",
+                r"\" => "\\\\",
+                "\\\"" => "\"", // no need to escape `"` in `'"'`
+                _ => ch,
+            }
+        );
+
+        Some(hint)
+    } else {
+        None
+    }
+}
+
 #[cfg(test)]
 mod test {
     use super::{reindent_multiline, without_block_comments};
diff --git a/tests/ui/manual_pattern_char_comparison.fixed b/tests/ui/manual_pattern_char_comparison.fixed
new file mode 100644
index 00000000000..588226b87e8
--- /dev/null
+++ b/tests/ui/manual_pattern_char_comparison.fixed
@@ -0,0 +1,49 @@
+#![warn(clippy::manual_pattern_char_comparison)]
+
+struct NotStr;
+
+impl NotStr {
+    fn find(&self, _: impl FnMut(char) -> bool) {}
+}
+
+fn main() {
+    let sentence = "Hello, world!";
+    sentence.trim_end_matches(['.', ',', '!', '?']);
+    sentence.split(['\n', 'X']);
+    sentence.split(['\n', 'X']);
+    sentence.splitn(3, 'X');
+    sentence.splitn(3, |c: char| c.is_whitespace() || c == 'X');
+    let char_compare = 'X';
+    sentence.splitn(3, char_compare);
+    sentence.split(['\n', 'X', 'Y']);
+    sentence.splitn(3, 'X');
+    sentence.splitn(3, ['X', 'W']);
+    sentence.find('🎈');
+
+    let not_str = NotStr;
+    not_str.find(|c: char| c == 'X');
+
+    "".find(|c| c == 'a' || c > 'z');
+
+    let x = true;
+    "".find(|c| c == 'a' || x || c == 'b');
+
+    let d = 'd';
+    "".find(|c| c == 'a' || d == 'b');
+
+    "".find(|c| match c {
+        'a' | 'b' => true,
+        _ => c.is_ascii(),
+    });
+
+    "".find(|c| matches!(c, 'a' | 'b' if false));
+
+    "".find(|c| matches!(c, 'a' | '1'..'4'));
+    "".find(|c| c == 'a' || matches!(c, '1'..'4'));
+    macro_rules! m {
+        ($e:expr) => {
+            $e == '?'
+        };
+    }
+    "".find(|c| m!(c));
+}
diff --git a/tests/ui/manual_pattern_char_comparison.rs b/tests/ui/manual_pattern_char_comparison.rs
new file mode 100644
index 00000000000..5078f3ee27f
--- /dev/null
+++ b/tests/ui/manual_pattern_char_comparison.rs
@@ -0,0 +1,49 @@
+#![warn(clippy::manual_pattern_char_comparison)]
+
+struct NotStr;
+
+impl NotStr {
+    fn find(&self, _: impl FnMut(char) -> bool) {}
+}
+
+fn main() {
+    let sentence = "Hello, world!";
+    sentence.trim_end_matches(|c: char| c == '.' || c == ',' || c == '!' || c == '?');
+    sentence.split(|c: char| c == '\n' || c == 'X');
+    sentence.split(|c| c == '\n' || c == 'X');
+    sentence.splitn(3, |c: char| c == 'X');
+    sentence.splitn(3, |c: char| c.is_whitespace() || c == 'X');
+    let char_compare = 'X';
+    sentence.splitn(3, |c: char| c == char_compare);
+    sentence.split(|c: char| matches!(c, '\n' | 'X' | 'Y'));
+    sentence.splitn(3, |c: char| matches!(c, 'X'));
+    sentence.splitn(3, |c: char| matches!(c, 'X' | 'W'));
+    sentence.find(|c| c == '🎈');
+
+    let not_str = NotStr;
+    not_str.find(|c: char| c == 'X');
+
+    "".find(|c| c == 'a' || c > 'z');
+
+    let x = true;
+    "".find(|c| c == 'a' || x || c == 'b');
+
+    let d = 'd';
+    "".find(|c| c == 'a' || d == 'b');
+
+    "".find(|c| match c {
+        'a' | 'b' => true,
+        _ => c.is_ascii(),
+    });
+
+    "".find(|c| matches!(c, 'a' | 'b' if false));
+
+    "".find(|c| matches!(c, 'a' | '1'..'4'));
+    "".find(|c| c == 'a' || matches!(c, '1'..'4'));
+    macro_rules! m {
+        ($e:expr) => {
+            $e == '?'
+        };
+    }
+    "".find(|c| m!(c));
+}
diff --git a/tests/ui/manual_pattern_char_comparison.stderr b/tests/ui/manual_pattern_char_comparison.stderr
new file mode 100644
index 00000000000..b6b51794a11
--- /dev/null
+++ b/tests/ui/manual_pattern_char_comparison.stderr
@@ -0,0 +1,59 @@
+error: this manual char comparison can be written more succinctly
+  --> tests/ui/manual_pattern_char_comparison.rs:11:31
+   |
+LL |     sentence.trim_end_matches(|c: char| c == '.' || c == ',' || c == '!' || c == '?');
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using an array of `char`: `['.', ',', '!', '?']`
+   |
+   = note: `-D clippy::manual-pattern-char-comparison` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::manual_pattern_char_comparison)]`
+
+error: this manual char comparison can be written more succinctly
+  --> tests/ui/manual_pattern_char_comparison.rs:12:20
+   |
+LL |     sentence.split(|c: char| c == '\n' || c == 'X');
+   |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using an array of `char`: `['\n', 'X']`
+
+error: this manual char comparison can be written more succinctly
+  --> tests/ui/manual_pattern_char_comparison.rs:13:20
+   |
+LL |     sentence.split(|c| c == '\n' || c == 'X');
+   |                    ^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using an array of `char`: `['\n', 'X']`
+
+error: this manual char comparison can be written more succinctly
+  --> tests/ui/manual_pattern_char_comparison.rs:14:24
+   |
+LL |     sentence.splitn(3, |c: char| c == 'X');
+   |                        ^^^^^^^^^^^^^^^^^^ help: consider using a `char`: `'X'`
+
+error: this manual char comparison can be written more succinctly
+  --> tests/ui/manual_pattern_char_comparison.rs:17:24
+   |
+LL |     sentence.splitn(3, |c: char| c == char_compare);
+   |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using a `char`: `char_compare`
+
+error: this manual char comparison can be written more succinctly
+  --> tests/ui/manual_pattern_char_comparison.rs:18:20
+   |
+LL |     sentence.split(|c: char| matches!(c, '\n' | 'X' | 'Y'));
+   |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using an array of `char`: `['\n', 'X', 'Y']`
+
+error: this manual char comparison can be written more succinctly
+  --> tests/ui/manual_pattern_char_comparison.rs:19:24
+   |
+LL |     sentence.splitn(3, |c: char| matches!(c, 'X'));
+   |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using a `char`: `'X'`
+
+error: this manual char comparison can be written more succinctly
+  --> tests/ui/manual_pattern_char_comparison.rs:20:24
+   |
+LL |     sentence.splitn(3, |c: char| matches!(c, 'X' | 'W'));
+   |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using an array of `char`: `['X', 'W']`
+
+error: this manual char comparison can be written more succinctly
+  --> tests/ui/manual_pattern_char_comparison.rs:21:19
+   |
+LL |     sentence.find(|c| c == '🎈');
+   |                   ^^^^^^^^^^^^^ help: consider using a `char`: `'🎈'`
+
+error: aborting due to 9 previous errors
+
diff --git a/tests/ui/search_is_some.rs b/tests/ui/search_is_some.rs
index e8a0920b645..9a9aaba56ad 100644
--- a/tests/ui/search_is_some.rs
+++ b/tests/ui/search_is_some.rs
@@ -1,5 +1,6 @@
 //@aux-build:option_helpers.rs
 #![warn(clippy::search_is_some)]
+#![allow(clippy::manual_pattern_char_comparison)]
 #![allow(clippy::useless_vec)]
 #![allow(dead_code)]
 extern crate option_helpers;
diff --git a/tests/ui/search_is_some.stderr b/tests/ui/search_is_some.stderr
index b5f84d23284..b5ef5534177 100644
--- a/tests/ui/search_is_some.stderr
+++ b/tests/ui/search_is_some.stderr
@@ -1,5 +1,5 @@
 error: called `is_some()` after searching an `Iterator` with `find`
-  --> tests/ui/search_is_some.rs:15:13
+  --> tests/ui/search_is_some.rs:16:13
    |
 LL |       let _ = v.iter().find(|&x| {
    |  _____________^
@@ -13,7 +13,7 @@ LL | |                    ).is_some();
    = help: to override `-D warnings` add `#[allow(clippy::search_is_some)]`
 
 error: called `is_some()` after searching an `Iterator` with `position`
-  --> tests/ui/search_is_some.rs:21:13
+  --> tests/ui/search_is_some.rs:22:13
    |
 LL |       let _ = v.iter().position(|&x| {
    |  _____________^
@@ -25,7 +25,7 @@ LL | |                    ).is_some();
    = help: this is more succinctly expressed by calling `any()`
 
 error: called `is_some()` after searching an `Iterator` with `rposition`
-  --> tests/ui/search_is_some.rs:27:13
+  --> tests/ui/search_is_some.rs:28:13
    |
 LL |       let _ = v.iter().rposition(|&x| {
    |  _____________^
@@ -37,13 +37,13 @@ LL | |                    ).is_some();
    = help: this is more succinctly expressed by calling `any()`
 
 error: called `is_some()` after searching an `Iterator` with `find`
-  --> tests/ui/search_is_some.rs:42:20
+  --> tests/ui/search_is_some.rs:43:20
    |
 LL |     let _ = (0..1).find(some_closure).is_some();
    |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `any(some_closure)`
 
 error: called `is_none()` after searching an `Iterator` with `find`
-  --> tests/ui/search_is_some.rs:52:13
+  --> tests/ui/search_is_some.rs:53:13
    |
 LL |       let _ = v.iter().find(|&x| {
    |  _____________^
@@ -55,7 +55,7 @@ LL | |                    ).is_none();
    = help: this is more succinctly expressed by calling `any()` with negation
 
 error: called `is_none()` after searching an `Iterator` with `position`
-  --> tests/ui/search_is_some.rs:58:13
+  --> tests/ui/search_is_some.rs:59:13
    |
 LL |       let _ = v.iter().position(|&x| {
    |  _____________^
@@ -67,7 +67,7 @@ LL | |                    ).is_none();
    = help: this is more succinctly expressed by calling `any()` with negation
 
 error: called `is_none()` after searching an `Iterator` with `rposition`
-  --> tests/ui/search_is_some.rs:64:13
+  --> tests/ui/search_is_some.rs:65:13
    |
 LL |       let _ = v.iter().rposition(|&x| {
    |  _____________^
@@ -79,7 +79,7 @@ LL | |                    ).is_none();
    = help: this is more succinctly expressed by calling `any()` with negation
 
 error: called `is_none()` after searching an `Iterator` with `find`
-  --> tests/ui/search_is_some.rs:79:13
+  --> tests/ui/search_is_some.rs:80:13
    |
 LL |     let _ = (0..1).find(some_closure).is_none();
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `!(0..1).any(some_closure)`