Fix lint_single_char_pattern on raw string literal

Author: tesuji

clippy_lints/src/methods/mod.rs

@@ -2329,13 +2329,20 @@ fn lint_chars_last_cmp_with_unwrap<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &
 fn lint_single_char_pattern<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, _expr: &'tcx hir::Expr, arg: &'tcx hir::Expr) {
     if_chain! {
         if let hir::ExprKind::Lit(lit) = &arg.node;
-        if let ast::LitKind::Str(r, _) = lit.node;
+        if let ast::LitKind::Str(r, style) = lit.node;
         if r.as_str().len() == 1;
         then {
             let mut applicability = Applicability::MachineApplicable;
             let snip = snippet_with_applicability(cx, arg.span, "..", &mut applicability);
-            let c = &snip[1..snip.len() - 1];
-            let hint = format!("'{}'", if c == "'" { "\\'" } else { c });
+            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!("'{}'", if ch == "'" { "\\'" } else { ch });
             span_lint_and_sugg(
                 cx,
                 SINGLE_CHAR_PATTERN,

tests/ui/single_char_pattern.fixed

@@ -53,4 +53,8 @@ fn main() {
     // Issue #3204
     const S: &str = "#";
     x.find(S);
+
+    // Raw string
+    x.split('a');
+    x.split('a');
 }

tests/ui/single_char_pattern.rs

@@ -53,4 +53,8 @@ fn main() {
     // Issue #3204
     const S: &str = "#";
     x.find(S);
+
+    // Raw string
+    x.split(r"a");
+    x.split(r#"a"#);
 }

tests/ui/single_char_pattern.stderr

@@ -132,5 +132,17 @@ error: single-character string constant used as pattern
 LL |     x.starts_with("/x03"); // issue #2996
    |                   ^^^^^^ help: try using a char instead: `'/x03'`
 
-error: aborting due to 22 previous errors
+error: single-character string constant used as pattern
+  --> $DIR/single_char_pattern.rs:58:13
+   |
+LL |     x.split(r"a");
+   |             ^^^^ help: try using a char instead: `'a'`
+
+error: single-character string constant used as pattern
+  --> $DIR/single_char_pattern.rs:59:13
+   |
+LL |     x.split(r#"a"#);
+   |             ^^^^^^ help: try using a char instead: `'a'`
+
+error: aborting due to 24 previous errors