feat(strlen_on_c_strings): mention the specific type (CString or CStr)

clippy_lints/src/strlen_on_c_strings.rs

@@ -1,4 +1,4 @@
-use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::diagnostics::span_lint_and_then;
 use clippy_utils::res::MaybeDef;
 use clippy_utils::source::snippet_with_context;
 use clippy_utils::visitors::is_expr_unsafe;
@@ -47,7 +47,21 @@ impl<'tcx> LateLintPass<'tcx> for StrlenOnCStrings {
             && let ExprKind::MethodCall(path, self_arg, [], _) = recv.kind
             && !recv.span.from_expansion()
             && path.ident.name == sym::as_ptr
+            && let typeck = cx.typeck_results()
+            && typeck
+                .expr_ty_adjusted(self_arg)
+                .peel_refs()
+                .is_lang_item(cx, LangItem::CStr)
         {
+            let ty = typeck.expr_ty(self_arg).peel_refs();
+            let ty_kind = if ty.is_diag_item(cx, sym::cstring_type) {
+                "`CString` value"
+            } else if ty.is_lang_item(cx, LangItem::CStr) {
+                "`CStr` value"
+            } else {
+                "type that dereferences to `CStr`"
+            };
+
             let ctxt = expr.span.ctxt();
             let span = match cx.tcx.parent_hir_node(expr.hir_id) {
                 Node::Block(&Block {
@@ -58,25 +72,16 @@ impl<'tcx> LateLintPass<'tcx> for StrlenOnCStrings {
                 _ => expr.span,
             };
 
-            let ty = cx.typeck_results().expr_ty(self_arg).peel_refs();
-            let mut app = Applicability::MachineApplicable;
-            let val_name = snippet_with_context(cx, self_arg.span, ctxt, "..", &mut app).0;
-            let method_name = if ty.is_diag_item(cx, sym::cstring_type) {
-                "as_bytes"
-            } else if ty.is_lang_item(cx, LangItem::CStr) {
-                "to_bytes"
-            } else {
-                return;
-            };
-
-            span_lint_and_sugg(
+            span_lint_and_then(
                 cx,
                 STRLEN_ON_C_STRINGS,
                 span,
-                "using `libc::strlen` on a `CString` or `CStr` value",
-                "try",
-                format!("{val_name}.{method_name}().len()"),
-                app,
+                format!("using `libc::strlen` on a {ty_kind}"),
+                |diag| {
+                    let mut app = Applicability::MachineApplicable;
+                    let val_name = snippet_with_context(cx, self_arg.span, ctxt, "_", &mut app).0;
+                    diag.span_suggestion(span, "use", format!("{val_name}.to_bytes().len()"), app);
+                },
             );
         }
     }

tests/ui/strlen_on_c_strings.fixed

@@ -1,37 +1,46 @@
 #![warn(clippy::strlen_on_c_strings)]
-#![allow(dead_code, clippy::manual_c_str_literals)]
+#![allow(clippy::manual_c_str_literals, clippy::boxed_local)]
 
-#[allow(unused)]
 use libc::strlen;
 use std::ffi::{CStr, CString};
 
 fn main() {
     // CString
     let cstring = CString::new("foo").expect("CString::new failed");
-    let _ = cstring.as_bytes().len();
-    //~^ strlen_on_c_strings
+    let _ = cstring.to_bytes().len();
+    //~^ ERROR: using `libc::strlen` on a `CString` value
 
     // CStr
     let cstr = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed");
     let _ = cstr.to_bytes().len();
-    //~^ strlen_on_c_strings
+    //~^ ERROR: using `libc::strlen` on a `CStr` value
 
     let _ = cstr.to_bytes().len();
-    //~^ strlen_on_c_strings
+    //~^ ERROR: using `libc::strlen` on a `CStr` value
 
     let pcstr: *const &CStr = &cstr;
     let _ = unsafe { (*pcstr).to_bytes().len() };
-    //~^ strlen_on_c_strings
+    //~^ ERROR: using `libc::strlen` on a `CStr` value
 
     unsafe fn unsafe_identity<T>(x: T) -> T {
         x
     }
     let _ = unsafe { unsafe_identity(cstr).to_bytes().len() };
-    //~^ strlen_on_c_strings
+    //~^ ERROR: using `libc::strlen` on a `CStr` value
     let _ = unsafe { unsafe_identity(cstr) }.to_bytes().len();
-    //~^ strlen_on_c_strings
+    //~^ ERROR: using `libc::strlen` on a `CStr` value
 
     let f: unsafe fn(_) -> _ = unsafe_identity;
     let _ = unsafe { f(cstr).to_bytes().len() };
-    //~^ strlen_on_c_strings
+    //~^ ERROR: using `libc::strlen` on a `CStr` value
+}
+
+// make sure we lint types that _adjust_ to `CStr`
+fn adjusted(box_cstring: Box<CString>, box_cstr: Box<CStr>, arc_cstring: std::sync::Arc<CStr>) {
+    let _ = box_cstring.to_bytes().len();
+    //~^ ERROR: using `libc::strlen` on a type that dereferences to `CStr`
+    let _ = box_cstr.to_bytes().len();
+    //~^ ERROR: using `libc::strlen` on a type that dereferences to `CStr`
+    let _ = arc_cstring.to_bytes().len();
+    //~^ ERROR: using `libc::strlen` on a type that dereferences to `CStr`
 }

tests/ui/strlen_on_c_strings.rs

@@ -1,37 +1,46 @@
 #![warn(clippy::strlen_on_c_strings)]
-#![allow(dead_code, clippy::manual_c_str_literals)]
+#![allow(clippy::manual_c_str_literals, clippy::boxed_local)]
 
-#[allow(unused)]
 use libc::strlen;
 use std::ffi::{CStr, CString};
 
 fn main() {
     // CString
     let cstring = CString::new("foo").expect("CString::new failed");
     let _ = unsafe { libc::strlen(cstring.as_ptr()) };
-    //~^ strlen_on_c_strings
+    //~^ ERROR: using `libc::strlen` on a `CString` value
 
     // CStr
     let cstr = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed");
     let _ = unsafe { libc::strlen(cstr.as_ptr()) };
-    //~^ strlen_on_c_strings
+    //~^ ERROR: using `libc::strlen` on a `CStr` value
 
     let _ = unsafe { strlen(cstr.as_ptr()) };
-    //~^ strlen_on_c_strings
+    //~^ ERROR: using `libc::strlen` on a `CStr` value
 
     let pcstr: *const &CStr = &cstr;
     let _ = unsafe { strlen((*pcstr).as_ptr()) };
-    //~^ strlen_on_c_strings
+    //~^ ERROR: using `libc::strlen` on a `CStr` value
 
     unsafe fn unsafe_identity<T>(x: T) -> T {
         x
     }
     let _ = unsafe { strlen(unsafe_identity(cstr).as_ptr()) };
-    //~^ strlen_on_c_strings
+    //~^ ERROR: using `libc::strlen` on a `CStr` value
     let _ = unsafe { strlen(unsafe { unsafe_identity(cstr) }.as_ptr()) };
-    //~^ strlen_on_c_strings
+    //~^ ERROR: using `libc::strlen` on a `CStr` value
 
     let f: unsafe fn(_) -> _ = unsafe_identity;
     let _ = unsafe { strlen(f(cstr).as_ptr()) };
-    //~^ strlen_on_c_strings
+    //~^ ERROR: using `libc::strlen` on a `CStr` value
+}
+
+// make sure we lint types that _adjust_ to `CStr`
+fn adjusted(box_cstring: Box<CString>, box_cstr: Box<CStr>, arc_cstring: std::sync::Arc<CStr>) {
+    let _ = unsafe { libc::strlen(box_cstring.as_ptr()) };
+    //~^ ERROR: using `libc::strlen` on a type that dereferences to `CStr`
+    let _ = unsafe { libc::strlen(box_cstr.as_ptr()) };
+    //~^ ERROR: using `libc::strlen` on a type that dereferences to `CStr`
+    let _ = unsafe { libc::strlen(arc_cstring.as_ptr()) };
+    //~^ ERROR: using `libc::strlen` on a type that dereferences to `CStr`
 }

tests/ui/strlen_on_c_strings.stderr

@@ -1,47 +1,65 @@
-error: using `libc::strlen` on a `CString` or `CStr` value
-  --> tests/ui/strlen_on_c_strings.rs:11:13
+error: using `libc::strlen` on a `CString` value
+  --> tests/ui/strlen_on_c_strings.rs:10:13
    |
 LL |     let _ = unsafe { libc::strlen(cstring.as_ptr()) };
-   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `cstring.as_bytes().len()`
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use: `cstring.to_bytes().len()`
    |
    = note: `-D clippy::strlen-on-c-strings` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::strlen_on_c_strings)]`
 
-error: using `libc::strlen` on a `CString` or `CStr` value
-  --> tests/ui/strlen_on_c_strings.rs:16:13
+error: using `libc::strlen` on a `CStr` value
+  --> tests/ui/strlen_on_c_strings.rs:15:13
    |
 LL |     let _ = unsafe { libc::strlen(cstr.as_ptr()) };
-   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `cstr.to_bytes().len()`
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use: `cstr.to_bytes().len()`
 
-error: using `libc::strlen` on a `CString` or `CStr` value
-  --> tests/ui/strlen_on_c_strings.rs:19:13
+error: using `libc::strlen` on a `CStr` value
+  --> tests/ui/strlen_on_c_strings.rs:18:13
    |
 LL |     let _ = unsafe { strlen(cstr.as_ptr()) };
-   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `cstr.to_bytes().len()`
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use: `cstr.to_bytes().len()`
 
-error: using `libc::strlen` on a `CString` or `CStr` value
-  --> tests/ui/strlen_on_c_strings.rs:23:22
+error: using `libc::strlen` on a `CStr` value
+  --> tests/ui/strlen_on_c_strings.rs:22:22
    |
 LL |     let _ = unsafe { strlen((*pcstr).as_ptr()) };
-   |                      ^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `(*pcstr).to_bytes().len()`
+   |                      ^^^^^^^^^^^^^^^^^^^^^^^^^ help: use: `(*pcstr).to_bytes().len()`
 
-error: using `libc::strlen` on a `CString` or `CStr` value
-  --> tests/ui/strlen_on_c_strings.rs:29:22
+error: using `libc::strlen` on a `CStr` value
+  --> tests/ui/strlen_on_c_strings.rs:28:22
    |
 LL |     let _ = unsafe { strlen(unsafe_identity(cstr).as_ptr()) };
-   |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `unsafe_identity(cstr).to_bytes().len()`
+   |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use: `unsafe_identity(cstr).to_bytes().len()`
 
-error: using `libc::strlen` on a `CString` or `CStr` value
-  --> tests/ui/strlen_on_c_strings.rs:31:13
+error: using `libc::strlen` on a `CStr` value
+  --> tests/ui/strlen_on_c_strings.rs:30:13
    |
 LL |     let _ = unsafe { strlen(unsafe { unsafe_identity(cstr) }.as_ptr()) };
-   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `unsafe { unsafe_identity(cstr) }.to_bytes().len()`
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use: `unsafe { unsafe_identity(cstr) }.to_bytes().len()`
 
-error: using `libc::strlen` on a `CString` or `CStr` value
-  --> tests/ui/strlen_on_c_strings.rs:35:22
+error: using `libc::strlen` on a `CStr` value
+  --> tests/ui/strlen_on_c_strings.rs:34:22
    |
 LL |     let _ = unsafe { strlen(f(cstr).as_ptr()) };
-   |                      ^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `f(cstr).to_bytes().len()`
+   |                      ^^^^^^^^^^^^^^^^^^^^^^^^ help: use: `f(cstr).to_bytes().len()`
 
-error: aborting due to 7 previous errors
+error: using `libc::strlen` on a type that dereferences to `CStr`
+  --> tests/ui/strlen_on_c_strings.rs:40:13
+   |
+LL |     let _ = unsafe { libc::strlen(box_cstring.as_ptr()) };
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use: `box_cstring.to_bytes().len()`
+
+error: using `libc::strlen` on a type that dereferences to `CStr`
+  --> tests/ui/strlen_on_c_strings.rs:42:13
+   |
+LL |     let _ = unsafe { libc::strlen(box_cstr.as_ptr()) };
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use: `box_cstr.to_bytes().len()`
+
+error: using `libc::strlen` on a type that dereferences to `CStr`
+  --> tests/ui/strlen_on_c_strings.rs:44:13
+   |
+LL |     let _ = unsafe { libc::strlen(arc_cstring.as_ptr()) };
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use: `arc_cstring.to_bytes().len()`
+
+error: aborting due to 10 previous errors