Fix strlen_on_c_strings when not used with a full path

clippy_utils/src/lib.rs

@@ -1597,6 +1597,14 @@ pub fn match_def_path<'tcx>(cx: &LateContext<'tcx>, did: DefId, syms: &[&str]) -
     syms.iter().map(|x| Symbol::intern(x)).eq(path.iter().copied())
 }
 
+/// Checks if the given `DefId` matches the `libc` item.
+pub fn match_libc_symbol(cx: &LateContext<'_>, did: DefId, name: &str) -> bool {
+    let path = cx.get_def_path(did);
+    // libc is meant to be used as a flat list of names, but they're all actually defined in different
+    // modules based on the target platform. Ignore everything but crate name and the item name.
+    path.first().map_or(false, |s| s.as_str() == "libc") && path.last().map_or(false, |s| s.as_str() == name)
+}
+
 pub fn match_panic_call(cx: &LateContext<'_>, expr: &'tcx Expr<'_>) -> Option<&'tcx Expr<'tcx>> {
     if let ExprKind::Call(func, [arg]) = expr.kind {
         expr_path_res(cx, func)

clippy_utils/src/paths.rs

@@ -86,7 +86,6 @@ pub const ITERTOOLS_NEXT_TUPLE: [&str; 3] = ["itertools", "Itertools", "next_tup
 pub const KW_MODULE: [&str; 3] = ["rustc_span", "symbol", "kw"];
 #[cfg(feature = "internal-lints")]
 pub const LATE_CONTEXT: [&str; 2] = ["rustc_lint", "LateContext"];
-pub const LIBC_STRLEN: [&str; 2] = ["libc", "strlen"];
 #[cfg(any(feature = "internal-lints", feature = "metadata-collector-lint"))]
 pub const LINT: [&str; 2] = ["rustc_lint_defs", "Lint"];
 pub const MEM_DISCRIMINANT: [&str; 3] = ["core", "mem", "discriminant"];