When not finding assoc fn on type, look for builder fn

When we have a resolution error when looking at a fully qualified path
on a type, look for all associated functions on inherent impls that
return `Self` and mention them to the user.

Fix #69512.

Author: estebank

compiler/rustc_hir_typeck/src/method/suggest.rs

@@ -409,6 +409,78 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             err.downgrade_to_delayed_bug();
         }
 
+        if let (ty::Adt(adt_def, _), SelfSource::QPath(_)) = (rcvr_ty.kind(), source) {
+            let mut items = self
+                .tcx
+                .inherent_impls(adt_def.did())
+                .iter()
+                .flat_map(|i| self.tcx.associated_items(i).in_definition_order())
+                .filter(|item| {
+                    matches!(item.kind, ty::AssocKind::Fn) && !item.fn_has_self_parameter
+                })
+                .filter_map(|item| {
+                    let ret_ty = self.tcx.fn_sig(item.def_id).skip_binder().output().skip_binder();
+                    let ty::Adt(def, args) = ret_ty.kind() else {
+                        return None;
+                    };
+                    if ![
+                        self.tcx.lang_items().option_type(),
+                        self.tcx.get_diagnostic_item(sym::Result),
+                    ]
+                    .contains(&Some(def.did()))
+                    {
+                        return None;
+                    }
+                    let arg = args.get(0)?;
+                    if self.can_eq(self.param_env, rcvr_ty, arg.expect_ty())
+                        || self.can_eq(self.param_env, ret_ty, rcvr_ty)
+                    {
+                        Some((item.def_id, ret_ty))
+                    } else {
+                        None
+                    }
+                })
+                .collect::<Vec<_>>();
+            let post = if items.len() > 9 {
+                let items_len = items.len();
+                items.truncate(8);
+                format!("and {} others", items_len - 8)
+            } else {
+                String::new()
+            };
+            match &items[..] {
+                [] => {}
+                [(def_id, ret_ty)] => {
+                    err.span_note(
+                        self.tcx.def_span(def_id),
+                        format!(
+                            "if you're trying to build a new `{rcvr_ty}`, consider using `{}` \
+                             which returns `{ret_ty}`",
+                            self.tcx.def_path_str(def_id),
+                        ),
+                    );
+                }
+                _ => {
+                    let span: MultiSpan = items
+                        .iter()
+                        .map(|(def_id, _)| self.tcx.def_span(def_id))
+                        .collect::<Vec<Span>>()
+                        .into();
+                    err.span_note(
+                        span,
+                        format!(
+                            "if you're trying to build a new `{rcvr_ty}` consider using one of the \
+                             following associated functions:\n{}{post}",
+                            items
+                                .iter()
+                                .map(|(def_id, _ret_ty)| self.tcx.def_path_str(def_id))
+                                .collect::<Vec<String>>()
+                                .join("\n")
+                        ),
+                    );
+                }
+            }
+        };
         if tcx.ty_is_opaque_future(rcvr_ty) && item_name.name == sym::poll {
             err.help(format!(
                 "method `poll` found on `Pin<&mut {ty_str}>`, \

tests/ui/issues/issue-42880.stderr

@@ -3,6 +3,13 @@ error[E0599]: no associated item named `String` found for struct `String` in the
    |
 LL |     let f = |&Value::String(_)| ();
    |                      ^^^^^^ associated item not found in `String`
+   |
+note: if you're trying to build a new `String` consider using one of the following associated functions:
+      String::from_utf8
+      String::from_utf16
+      String::from_utf16le
+      String::from_utf16be
+  --> $SRC_DIR/alloc/src/string.rs:LL:COL
 
 error: aborting due to previous error
 

tests/ui/resolve/fn-new-doesnt-exist.rs

@@ -0,0 +1,5 @@
+use std::net::TcpStream;
+
+fn main() {
+   let stream = TcpStream::new(); //~ ERROR no function or associated item named `new` found
+}

tests/ui/resolve/fn-new-doesnt-exist.stderr

@@ -0,0 +1,14 @@
+error[E0599]: no function or associated item named `new` found for struct `TcpStream` in the current scope
+  --> $DIR/fn-new-doesnt-exist.rs:4:28
+   |
+LL |    let stream = TcpStream::new();
+   |                            ^^^ function or associated item not found in `TcpStream`
+   |
+note: if you're trying to build a new `TcpStream` consider using one of the following associated functions:
+      TcpStream::connect
+      TcpStream::connect_timeout
+  --> $SRC_DIR/std/src/net/tcp.rs:LL:COL
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0599`.

tests/ui/resolve/issue-82865.stderr

@@ -15,6 +15,16 @@ LL |     Box::z
 LL |     mac!();
    |     ------ in this macro invocation
    |
+note: if you're trying to build a new `Box<_, _>` consider using one of the following associated functions:
+      Box::<T>::try_new
+      Box::<T>::try_new_uninit
+      Box::<T>::try_new_zeroed
+      Box::<T, A>::try_new_in
+      Box::<T, A>::try_new_uninit_in
+      Box::<T, A>::try_new_zeroed_in
+      Box::<[T]>::try_new_uninit_slice
+      Box::<[T]>::try_new_zeroed_slice
+  --> $SRC_DIR/alloc/src/boxed.rs:LL:COL
    = note: this error originates in the macro `mac` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 2 previous errors