Auto merge of #13313 - y21:issue13308, r=Centri3

Look at adjusted types instead of fn signature types in `ptr_arg`

This simplifies the implementation of the `ptr_arg` lint a bit and:
Fixes #13308
Fixes #10612

Currently, the lint checks if e.g. a `&String` parameter is only used in contexts where a `&str` could work. Part of it worked by looking for path exprs to that parameter in function call position specifically, looking at the callee signature and checking if that parameter type without refs is `String` (or one of a bunch of other special cases).

This simplified version removes the special casing of function calls and looking at the parameter type and instead just looks at the **adjusted type**, regardless of the expression it's in. This naturally also covers what the previous version was doing (if the expression is in a function call argument position expecting a `&str`, then it will have that adjustment. If it requires a `&String` then it won't have that adjustment and we won't lint).

The linked issue was a FP that happened because the previous implementation simply didn't consider projection types in the signature type, but with this simplification we don't really need to consider that (because we aren't looking at function signatures at all anymore -- the `&mut Self::Owned` parameter type of `clone_into` is the already-instantiated and normalized type `&mut String`).

changelog: none

3 files changed, 75 insertions, 61 deletions

diff --git a/clippy_lints/src/ptr.rs b/clippy_lints/src/ptr.rs
index 7d24d25dc2f..cd8e921347c 100644
--- a/clippy_lints/src/ptr.rs
+++ b/clippy_lints/src/ptr.rs
@@ -1,11 +1,9 @@
 use clippy_utils::diagnostics::{span_lint, span_lint_and_sugg, span_lint_and_then, span_lint_hir_and_then};
 use clippy_utils::source::SpanRangeExt;
-use clippy_utils::ty::expr_sig;
 use clippy_utils::visitors::contains_unsafe_block;
 use clippy_utils::{get_expr_use_or_unification_node, is_lint_allowed, path_def_id, path_to_local};
 use hir::LifetimeName;
 use rustc_errors::{Applicability, MultiSpan};
-use rustc_hir::def_id::DefId;
 use rustc_hir::hir_id::{HirId, HirIdMap};
 use rustc_hir::intravisit::{walk_expr, Visitor};
 use rustc_hir::{
@@ -323,7 +321,6 @@ struct PtrArg<'tcx> {
     idx: usize,
     emission_id: HirId,
     span: Span,
-    ty_did: DefId,
     ty_name: Symbol,
     method_renames: &'static [(&'static str, &'static str)],
     ref_prefix: RefPrefix,
@@ -411,7 +408,6 @@ impl<'tcx> DerefTy<'tcx> {
     }
 }
 
-#[expect(clippy::too_many_lines)]
 fn check_fn_args<'cx, 'tcx: 'cx>(
     cx: &'cx LateContext<'tcx>,
     fn_sig: ty::FnSig<'tcx>,
@@ -514,7 +510,6 @@ fn check_fn_args<'cx, 'tcx: 'cx>(
                     idx: i,
                     emission_id,
                     span: hir_ty.span,
-                    ty_did: adt.did(),
                     ty_name: name.ident.name,
                     method_renames,
                     ref_prefix: RefPrefix { lt: *lt, mutability },
@@ -610,65 +605,50 @@ fn check_ptr_arg_usage<'tcx>(cx: &LateContext<'tcx>, body: &Body<'tcx>, args: &[
                         set_skip_flag();
                     }
                 },
-                Some((Node::Expr(e), child_id)) => match e.kind {
-                    ExprKind::Call(f, expr_args) => {
-                        let i = expr_args.iter().position(|arg| arg.hir_id == child_id).unwrap_or(0);
-                        if expr_sig(self.cx, f).and_then(|sig| sig.input(i)).map_or(true, |ty| {
-                            match *ty.skip_binder().peel_refs().kind() {
-                                ty::Dynamic(preds, _, _) => !matches_preds(self.cx, args.deref_ty.ty(self.cx), preds),
-                                ty::Param(_) => true,
-                                ty::Adt(def, _) => def.did() == args.ty_did,
-                                _ => false,
-                            }
-                        }) {
-                            // Passed to a function taking the non-dereferenced type.
-                            set_skip_flag();
-                        }
-                    },
-                    ExprKind::MethodCall(name, self_arg, expr_args, _) => {
-                        let i = iter::once(self_arg)
-                            .chain(expr_args.iter())
-                            .position(|arg| arg.hir_id == child_id)
-                            .unwrap_or(0);
-                        if i == 0 {
-                            // Check if the method can be renamed.
-                            let name = name.ident.as_str();
-                            if let Some((_, replacement)) = args.method_renames.iter().find(|&&(x, _)| x == name) {
-                                result.replacements.push(PtrArgReplacement {
-                                    expr_span: e.span,
-                                    self_span: self_arg.span,
-                                    replacement,
-                                });
-                                return;
-                            }
+                Some((Node::Expr(use_expr), child_id)) => {
+                    if let ExprKind::Index(e, ..) = use_expr.kind
+                        && e.hir_id == child_id
+                    {
+                        // Indexing works with both owned and its dereferenced type
+                        return;
+                    }
+
+                    if let ExprKind::MethodCall(name, receiver, ..) = use_expr.kind
+                        && receiver.hir_id == child_id
+                    {
+                        let name = name.ident.as_str();
+
+                        // Check if the method can be renamed.
+                        if let Some((_, replacement)) = args.method_renames.iter().find(|&&(x, _)| x == name) {
+                            result.replacements.push(PtrArgReplacement {
+                                expr_span: use_expr.span,
+                                self_span: receiver.span,
+                                replacement,
+                            });
+                            return;
                         }
 
-                        let Some(id) = self.cx.typeck_results().type_dependent_def_id(e.hir_id) else {
-                            set_skip_flag();
+                        // Some methods exist on both `[T]` and `Vec<T>`, such as `len`, where the receiver type
+                        // doesn't coerce to a slice and our adjusted type check below isn't enough,
+                        // but it would still be valid to call with a slice
+                        if is_allowed_vec_method(self.cx, use_expr) {
                             return;
-                        };
-
-                        match *self.cx.tcx.fn_sig(id).instantiate_identity().skip_binder().inputs()[i]
-                            .peel_refs()
-                            .kind()
-                        {
-                            ty::Dynamic(preds, _, _) if !matches_preds(self.cx, args.deref_ty.ty(self.cx), preds) => {
-                                set_skip_flag();
-                            },
-                            ty::Param(_) => {
-                                set_skip_flag();
-                            },
-                            // If the types match check for methods which exist on both types. e.g. `Vec::len` and
-                            // `slice::len`
-                            ty::Adt(def, _) if def.did() == args.ty_did && !is_allowed_vec_method(self.cx, e) => {
-                                set_skip_flag();
-                            },
-                            _ => (),
                         }
-                    },
-                    // Indexing is fine for currently supported types.
-                    ExprKind::Index(e, _, _) if e.hir_id == child_id => (),
-                    _ => set_skip_flag(),
+                    }
+
+                    let deref_ty = args.deref_ty.ty(self.cx);
+                    let adjusted_ty = self.cx.typeck_results().expr_ty_adjusted(e).peel_refs();
+                    if adjusted_ty == deref_ty {
+                        return;
+                    }
+
+                    if let ty::Dynamic(preds, ..) = adjusted_ty.kind()
+                        && matches_preds(self.cx, deref_ty, preds)
+                    {
+                        return;
+                    }
+
+                    set_skip_flag();
                 },
                 _ => set_skip_flag(),
             }
diff --git a/tests/ui/ptr_arg.rs b/tests/ui/ptr_arg.rs
index e6ef6268121..e8b42d3b913 100644
--- a/tests/ui/ptr_arg.rs
+++ b/tests/ui/ptr_arg.rs
@@ -309,3 +309,25 @@ mod issue_11181 {
         extern "C" fn allowed(_v: &Vec<u32>) {}
     }
 }
+
+mod issue_13308 {
+    use std::ops::Deref;
+
+    fn repro(source: &str, destination: &mut String) {
+        source.clone_into(destination);
+    }
+    fn repro2(source: &str, destination: &mut String) {
+        ToOwned::clone_into(source, destination);
+    }
+
+    fn h1(_: &<String as Deref>::Target) {}
+    fn h2<T: Deref>(_: T, _: &T::Target) {}
+
+    // Other cases that are still ok to lint and ideally shouldn't regress
+    fn good(v1: &String, v2: &String) {
+        //~^ ERROR: writing `&String` instead of `&str`
+        //~^^ ERROR: writing `&String` instead of `&str`
+        h1(v1);
+        h2(String::new(), v2);
+    }
+}
diff --git a/tests/ui/ptr_arg.stderr b/tests/ui/ptr_arg.stderr
index 4246453e64c..1a6b3aa1f8d 100644
--- a/tests/ui/ptr_arg.stderr
+++ b/tests/ui/ptr_arg.stderr
@@ -221,5 +221,17 @@ error: using a reference to `Cow` is not recommended
 LL |     fn cow_bad_ret_ty_2<'a, 'b>(input: &'a Cow<'a, str>) -> &'b str {
    |                                        ^^^^^^^^^^^^^^^^ help: change this to: `&str`
 
-error: aborting due to 25 previous errors
+error: writing `&String` instead of `&str` involves a new object where a slice will do
+  --> tests/ui/ptr_arg.rs:327:17
+   |
+LL |     fn good(v1: &String, v2: &String) {
+   |                 ^^^^^^^ help: change this to: `&str`
+
+error: writing `&String` instead of `&str` involves a new object where a slice will do
+  --> tests/ui/ptr_arg.rs:327:30
+   |
+LL |     fn good(v1: &String, v2: &String) {
+   |                              ^^^^^^^ help: change this to: `&str`
+
+error: aborting due to 27 previous errors