add checking type

adding test patterns

cargo dev bless

fix comment

add ;

delete :

fix suggestion code

and update stderr in tests.

use match_def_path when checking method name

clippy_lints/src/bytes_count_to_len.rs

@@ -1,8 +1,14 @@
-use clippy_utils::diagnostics::span_lint_and_note;
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::source::snippet_with_applicability;
+use clippy_utils::ty::is_type_diagnostic_item;
+use clippy_utils::{match_def_path, paths};
 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};
+use rustc_span::sym;
 
 declare_clippy_lint! {
     /// ### What it does
@@ -16,15 +22,17 @@ declare_clippy_lint! {
     /// ### Example
     /// ```rust
     /// "hello".bytes().count();
+    /// String::from("hello").bytes().count();
     /// ```
     /// Use instead:
     /// ```rust
     /// "hello".len();
+    /// String::from("hello").len();
     /// ```
-    #[clippy::version = "1.60.0"]
+    #[clippy::version = "1.62.0"]
     pub BYTES_COUNT_TO_LEN,
     complexity,
-    "Using bytest().count() when len() performs the same functionality"
+    "Using `bytes().count()` when `len()` performs the same functionality"
 }
 
 declare_lint_pass!(BytesCountToLen => [BYTES_COUNT_TO_LEN]);
@@ -32,21 +40,29 @@ declare_lint_pass!(BytesCountToLen => [BYTES_COUNT_TO_LEN]);
 impl<'tcx> LateLintPass<'tcx> for BytesCountToLen {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
         if_chain! {
-            //check for method call called "count"
+            if let hir::ExprKind::MethodCall(_, expr_args, _) = &expr.kind;
-            if let hir::ExprKind::MethodCall(count_path, count_args, _) = &expr.kind;
+            if let Some(expr_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
-            if count_path.ident.name == rustc_span::sym::count;
+            if match_def_path(cx, expr_def_id, &paths::ITER_COUNT);
-            if let [bytes_expr] = &**count_args;
+
-            //check for method call called "bytes" that was linked to "count"
+            if let [bytes_expr] = &**expr_args;
-            if let hir::ExprKind::MethodCall(bytes_path, _, _) = &bytes_expr.kind;
+            if let hir::ExprKind::MethodCall(_, bytes_args, _) = &bytes_expr.kind;
-            if bytes_path.ident.name.as_str() == "bytes";
+            if let Some(bytes_def_id) = cx.typeck_results().type_dependent_def_id(bytes_expr.hir_id);
+            if match_def_path(cx, bytes_def_id, &paths::STR_BYTES);
+
+            if let [str_expr] = &**bytes_args;
+            let ty = cx.typeck_results().expr_ty(str_expr).peel_refs();
+
+            if is_type_diagnostic_item(cx, ty, sym::String) || ty.kind() == &ty::Str;
             then {
-                span_lint_and_note(
+                let mut applicability = Applicability::MachineApplicable;
+                span_lint_and_sugg(
                     cx,
                     BYTES_COUNT_TO_LEN,
                     expr.span,
                     "using long and hard to read `.bytes().count()`",
-                    None,
+                    "consider calling `.len()` instead",
-                    "`.len()` achieves same functionality"
+                    format!("{}.len()", snippet_with_applicability(cx, str_expr.span, "..", &mut applicability)),
+                    applicability
                 );
             }
         };

clippy_utils/src/paths.rs

@@ -61,6 +61,7 @@ pub const IO_READ: [&str; 3] = ["std", "io", "Read"];
 pub const IO_WRITE: [&str; 3] = ["std", "io", "Write"];
 pub const IPADDR_V4: [&str; 5] = ["std", "net", "ip", "IpAddr", "V4"];
 pub const IPADDR_V6: [&str; 5] = ["std", "net", "ip", "IpAddr", "V6"];
+pub const ITER_COUNT: [&str; 6] = ["core", "iter", "traits", "iterator", "Iterator", "count"];
 pub const ITER_REPEAT: [&str; 5] = ["core", "iter", "sources", "repeat", "repeat"];
 #[allow(clippy::invalid_paths)] // internal lints do not know about all external crates
 pub const ITERTOOLS_NEXT_TUPLE: [&str; 3] = ["itertools", "Itertools", "next_tuple"];
@@ -149,6 +150,7 @@ pub const STD_FS_CREATE_DIR: [&str; 3] = ["std", "fs", "create_dir"];
 pub const STRING_AS_MUT_STR: [&str; 4] = ["alloc", "string", "String", "as_mut_str"];
 pub const STRING_AS_STR: [&str; 4] = ["alloc", "string", "String", "as_str"];
 pub const STRING_NEW: [&str; 4] = ["alloc", "string", "String", "new"];
+pub const STR_BYTES: [&str; 4] = ["core", "str", "<impl str>", "bytes"];
 pub const STR_ENDS_WITH: [&str; 4] = ["core", "str", "<impl str>", "ends_with"];
 pub const STR_FROM_UTF8: [&str; 4] = ["core", "str", "converts", "from_utf8"];
 pub const STR_LEN: [&str; 4] = ["core", "str", "<impl str>", "len"];

tests/ui/bytes_count_to_len.fixed

@@ -0,0 +1,34 @@
+// run-rustfix
+#![warn(clippy::bytes_count_to_len)]
+use std::fs::File;
+use std::io::Read;
+
+fn main() {
+    // should fix, because type is String
+    let _ = String::from("foo").len();
+
+    let s1 = String::from("foo");
+    let _ = s1.len();
+
+    // should fix, because type is &str
+    let _ = "foo".len();
+
+    let s2 = "foo";
+    let _ = s2.len();
+
+    // make sure using count() normally doesn't trigger warning
+    let vector = [0, 1, 2];
+    let _ = vector.iter().count();
+
+    // The type is slice, so should not fix
+    let _ = &[1, 2, 3].bytes().count();
+
+    let bytes: &[u8] = &[1, 2, 3];
+    bytes.bytes().count();
+
+    // The type is File, so should not fix
+    let _ = File::open("foobar").unwrap().bytes().count();
+
+    let f = File::open("foobar").unwrap();
+    let _ = f.bytes().count();
+}

tests/ui/bytes_count_to_len.rs

@@ -1,15 +1,34 @@
+// run-rustfix
 #![warn(clippy::bytes_count_to_len)]
+use std::fs::File;
+use std::io::Read;
 
 fn main() {
-    let s1 = String::from("world");
+    // should fix, because type is String
+    let _ = String::from("foo").bytes().count();
 
-    //test warning against a string literal
+    let s1 = String::from("foo");
-    "hello".bytes().count();
+    let _ = s1.bytes().count();
 
-    //test warning against a string variable
+    // should fix, because type is &str
-    s1.bytes().count();
+    let _ = "foo".bytes().count();
 
-    //make sure using count() normally doesn't trigger warning
+    let s2 = "foo";
+    let _ = s2.bytes().count();
+
+    // make sure using count() normally doesn't trigger warning
     let vector = [0, 1, 2];
-    let size = vector.iter().count();
+    let _ = vector.iter().count();
+
+    // The type is slice, so should not fix
+    let _ = &[1, 2, 3].bytes().count();
+
+    let bytes: &[u8] = &[1, 2, 3];
+    bytes.bytes().count();
+
+    // The type is File, so should not fix
+    let _ = File::open("foobar").unwrap().bytes().count();
+
+    let f = File::open("foobar").unwrap();
+    let _ = f.bytes().count();
 }

tests/ui/bytes_count_to_len.stderr

@@ -1,19 +1,28 @@
 error: using long and hard to read `.bytes().count()`
-  --> $DIR/bytes_count_to_len.rs:7:5
+  --> $DIR/bytes_count_to_len.rs:8:13
    |
-LL |     "hello".bytes().count();
+LL |     let _ = String::from("foo").bytes().count();
-   |     ^^^^^^^^^^^^^^^^^^^^^^^
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider calling `.len()` instead: `String::from("foo").len()`
    |
    = note: `-D clippy::bytes-count-to-len` implied by `-D warnings`
-   = note: `.len()` achieves same functionality
 
 error: using long and hard to read `.bytes().count()`
-  --> $DIR/bytes_count_to_len.rs:10:5
+  --> $DIR/bytes_count_to_len.rs:11:13
    |
-LL |     s1.bytes().count();
+LL |     let _ = s1.bytes().count();
-   |     ^^^^^^^^^^^^^^^^^^
+   |             ^^^^^^^^^^^^^^^^^^ help: consider calling `.len()` instead: `s1.len()`
+
+error: using long and hard to read `.bytes().count()`
+  --> $DIR/bytes_count_to_len.rs:14:13
    |
-   = note: `.len()` achieves same functionality
+LL |     let _ = "foo".bytes().count();
+   |             ^^^^^^^^^^^^^^^^^^^^^ help: consider calling `.len()` instead: `"foo".len()`
 
-error: aborting due to 2 previous errors
+error: using long and hard to read `.bytes().count()`
+  --> $DIR/bytes_count_to_len.rs:17:13
+   |
+LL |     let _ = s2.bytes().count();
+   |             ^^^^^^^^^^^^^^^^^^ help: consider calling `.len()` instead: `s2.len()`
+
+error: aborting due to 4 previous errors