When encountering struct fn call literal with private fields, suggest all builders

When encountering code like `Box(42)`, suggest `Box::new(42)` and *all*
other associated functions that return `-> Box<T>`.

compiler/rustc_errors/src/diagnostic.rs

@@ -759,6 +759,9 @@ impl Diagnostic {
         suggestions: impl IntoIterator<Item = String>,
         applicability: Applicability,
     ) -> &mut Self {
+        let mut suggestions: Vec<_> = suggestions.into_iter().collect();
+        suggestions.sort();
+
         self.span_suggestions_with_style(
             sp,
             msg,
@@ -768,7 +771,9 @@ impl Diagnostic {
         )
     }
 
-    /// [`Diagnostic::span_suggestions()`] but you can set the [`SuggestionStyle`].
+    /// [`Diagnostic::span_suggestions()`] but you can set the [`SuggestionStyle`]. This version
+    /// *doesn't* sort the suggestions, so the caller has control of the order in which they are
+    /// presented.
     pub fn span_suggestions_with_style(
         &mut self,
         sp: Span,
@@ -777,9 +782,7 @@ impl Diagnostic {
         applicability: Applicability,
         style: SuggestionStyle,
     ) -> &mut Self {
-        let mut suggestions: Vec<_> = suggestions.into_iter().collect();
-        suggestions.sort();
-
+        let suggestions: Vec<_> = suggestions.into_iter().collect();
         debug_assert!(
             !(sp.is_empty() && suggestions.iter().any(|suggestion| suggestion.is_empty())),
             "Span must not be empty and have no suggestion"

compiler/rustc_macros/src/diagnostics/diagnostic_builder.rs

@@ -442,10 +442,12 @@ impl<'a> DiagnosticDeriveVariantBuilder<'a> {
 
                 self.formatting_init.extend(code_init);
                 Ok(quote! {
+                    let mut code: Vec<_> = #code_field.into_iter().collect();
+                    code.sort();
                     #diag.span_suggestions_with_style(
                         #span_field,
                         crate::fluent_generated::#slug,
-                        #code_field,
+                        code,
                         #applicability,
                         #style
                     );

compiler/rustc_resolve/src/diagnostics.rs

@@ -2608,6 +2608,7 @@ fn show_candidates(
         path_strings.extend(core_path_strings);
         path_strings.dedup_by(|a, b| a.0 == b.0);
     }
+    accessible_path_strings.sort();
 
     if !accessible_path_strings.is_empty() {
         let (determiner, kind, name, through) =

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -15,7 +15,7 @@ use rustc_ast_pretty::pprust::where_bound_predicate_to_string;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::{
     pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed,
-    MultiSpan,
+    MultiSpan, SuggestionStyle,
 };
 use rustc_hir as hir;
 use rustc_hir::def::{self, CtorKind, CtorOf, DefKind};
@@ -29,6 +29,8 @@ use rustc_span::hygiene::MacroKind;
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::Span;
 
+use rustc_middle::ty;
+
 use std::borrow::Cow;
 use std::iter;
 use std::ops::Deref;
@@ -1593,29 +1595,85 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
                         Some(Vec::from(pattern_spans))
                     }
                     // e.g. `let _ = Enum::TupleVariant(field1, field2);`
-                    _ if source.is_call() => {
+                    PathSource::Expr(Some(Expr { kind: ExprKind::Call(_, ref args), .. })) => {
                         err.set_primary_message(
                             "cannot initialize a tuple struct which contains private fields",
                         );
-                        if !def_id.is_local()
-                            && self
+                        if !def_id.is_local() {
+                            // Look at all the associated functions without receivers in the type's
+                            // inherent impls to look for builders that return `Self`
+                            let mut items = self
                                 .r
                                 .tcx
                                 .inherent_impls(def_id)
                                 .iter()
-                                .flat_map(|impl_def_id| {
-                                    self.r.tcx.provided_trait_methods(*impl_def_id)
+                                .flat_map(|i| self.r.tcx.associated_items(i).in_definition_order())
+                                // Only assoc fn with no receivers.
+                                .filter(|item| {
+                                    matches!(item.kind, ty::AssocKind::Fn)
+                                        && !item.fn_has_self_parameter
                                 })
-                                .any(|assoc| !assoc.fn_has_self_parameter && assoc.name == sym::new)
-                        {
-                            // FIXME: look for associated functions with Self return type,
-                            // instead of relying only on the name and lack of self receiver.
-                            err.span_suggestion_verbose(
-                                span.shrink_to_hi(),
-                                "you might have meant to use the `new` associated function",
-                                "::new".to_string(),
-                                Applicability::MaybeIncorrect,
-                            );
+                                .filter_map(|item| {
+                                    // Only assoc fns that return `Self`
+                                    let fn_sig = self.r.tcx.fn_sig(item.def_id).skip_binder();
+                                    let ret_ty = fn_sig.output();
+                                    let ret_ty = self.r.tcx.erase_late_bound_regions(ret_ty);
+                                    let ty::Adt(def, _args) = ret_ty.kind() else {
+                                        return None;
+                                    };
+                                    // Check for `-> Self`
+                                    if def.did() == def_id {
+                                        let order = if item.name.as_str().starts_with("new")
+                                            && fn_sig.inputs().skip_binder().len() == args.len()
+                                        {
+                                            0
+                                        } else if item.name.as_str().starts_with("new")
+                                            || item.name.as_str().starts_with("default")
+                                        {
+                                            // Give higher precedence to functions with a name that
+                                            // imply construction.
+                                            1
+                                        } else if fn_sig.inputs().skip_binder().len() == args.len()
+                                        {
+                                            2
+                                        } else {
+                                            3
+                                        };
+                                        return Some((order, item.name));
+                                    }
+                                    None
+                                })
+                                .collect::<Vec<_>>();
+                            items.sort_by_key(|(order, _)| *order);
+                            match &items[..] {
+                                [] => {}
+                                [(_, name)] => {
+                                    err.span_suggestion_verbose(
+                                        span.shrink_to_hi(),
+                                        format!(
+                                            "you might have meant to use the `{name}` associated \
+                                             function",
+                                        ),
+                                        format!("::{name}"),
+                                        Applicability::MaybeIncorrect,
+                                    );
+                                }
+                                _ => {
+                                    // We use this instead of `span_suggestions` to retain output
+                                    // sort order.
+                                    err.span_suggestions_with_style(
+                                        span.shrink_to_hi(),
+                                        "you might have meant to use an associated function to \
+                                         build this type",
+                                        items
+                                            .iter()
+                                            .map(|(_, name)| format!("::{name}"))
+                                            .collect::<Vec<String>>(),
+                                        Applicability::MaybeIncorrect,
+                                        SuggestionStyle::ShowAlways,
+                                    );
+                                }
+                            }
                         }
                         // Use spans of the tuple struct definition.
                         self.r.field_def_ids(def_id).map(|field_ids| {

tests/ui/hygiene/extern-prelude-from-opaque-fail-2018.stderr

@@ -25,8 +25,8 @@ LL | a!();
    | ---- in this macro invocation
    |
    = help: consider importing one of these items:
-           std::mem
            core::mem
+           std::mem
    = note: this error originates in the macro `a` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0433]: failed to resolve: use of undeclared crate or module `my_core`

tests/ui/privacy/suggest-box-new.fixed

@@ -1,15 +0,0 @@
-// run-rustfix
-#![allow(dead_code)]
-struct U <T> {
-    wtf: Option<Box<U<T>>>,
-    x: T,
-}
-fn main() {
-    U {
-        wtf: Some(Box::new(U { //~ ERROR cannot initialize a tuple struct which contains private fields
-            wtf: None,
-            x: (),
-        })),
-        x: ()
-    };
-}

tests/ui/privacy/suggest-box-new.rs

@@ -1,4 +1,3 @@
-// run-rustfix
 #![allow(dead_code)]
 struct U <T> {
     wtf: Option<Box<U<T>>>,

tests/ui/privacy/suggest-box-new.stderr

@@ -1,5 +1,5 @@
 error[E0423]: cannot initialize a tuple struct which contains private fields
-  --> $DIR/suggest-box-new.rs:9:19
+  --> $DIR/suggest-box-new.rs:8:19
    |
 LL |         wtf: Some(Box(U {
    |                   ^^^
@@ -10,10 +10,17 @@ note: constructor is not visible here due to private fields
    = note: private field
    |
    = note: private field
-help: you might have meant to use the `new` associated function
+help: you might have meant to use an associated function to build this type
    |
 LL |         wtf: Some(Box::new(U {
    |                      +++++
+LL |         wtf: Some(Box::new_uninit_in(U {
+   |                      +++++++++++++++
+LL |         wtf: Some(Box::new_zeroed_in(U {
+   |                      +++++++++++++++
+LL |         wtf: Some(Box::new_uninit_slice(U {
+   |                      ++++++++++++++++++
+     and 10 other candidates
 
 error: aborting due to previous error
 

tests/ui/suggestions/suggest-tryinto-edition-change.stderr

@@ -4,8 +4,8 @@ error[E0433]: failed to resolve: use of undeclared type `TryFrom`
 LL |     let _i: i16 = TryFrom::try_from(0_i32).unwrap();
    |                   ^^^^^^^ use of undeclared type `TryFrom`
    |
-   = note: 'std::convert::TryFrom' is included in the prelude starting in Edition 2021
    = note: 'core::convert::TryFrom' is included in the prelude starting in Edition 2021
+   = note: 'std::convert::TryFrom' is included in the prelude starting in Edition 2021
 help: consider importing one of these items
    |
 LL + use core::convert::TryFrom;
@@ -19,8 +19,8 @@ error[E0433]: failed to resolve: use of undeclared type `TryInto`
 LL |     let _i: i16 = TryInto::try_into(0_i32).unwrap();
    |                   ^^^^^^^ use of undeclared type `TryInto`
    |
-   = note: 'std::convert::TryInto' is included in the prelude starting in Edition 2021
    = note: 'core::convert::TryInto' is included in the prelude starting in Edition 2021
+   = note: 'std::convert::TryInto' is included in the prelude starting in Edition 2021
 help: consider importing one of these items
    |
 LL + use core::convert::TryInto;
@@ -34,8 +34,8 @@ error[E0433]: failed to resolve: use of undeclared type `FromIterator`
 LL |     let _v: Vec<_> = FromIterator::from_iter(&[1]);
    |                      ^^^^^^^^^^^^ use of undeclared type `FromIterator`
    |
-   = note: 'std::iter::FromIterator' is included in the prelude starting in Edition 2021
    = note: 'core::iter::FromIterator' is included in the prelude starting in Edition 2021
+   = note: 'std::iter::FromIterator' is included in the prelude starting in Edition 2021
 help: a trait with a similar name exists
    |
 LL |     let _v: Vec<_> = IntoIterator::from_iter(&[1]);