fix #101749, use . instead of :: when accessing a method of an object

compiler/rustc_errors/src/lib.rs

@@ -467,6 +467,7 @@ pub enum StashKey {
     /// When an invalid lifetime e.g. `'2` should be reinterpreted
     /// as a char literal in the parser
     LifetimeIsChar,
+    CallAssocMethod,
 }
 
 fn default_track_diagnostic(_: &Diagnostic) {}

compiler/rustc_hir_typeck/src/expr.rs

@@ -527,6 +527,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             self.resolve_ty_and_res_fully_qualified_call(qpath, expr.hir_id, expr.span);
         let ty = match res {
             Res::Err => {
+                self.suggest_assoc_method_call(segs);
                 let e =
                     self.tcx.sess.delay_span_bug(qpath.span(), "`Res::Err` but no error emitted");
                 self.set_tainted_by_errors(e);

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

@@ -1043,7 +1043,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         hir_id: hir::HirId,
     ) -> (Ty<'tcx>, Res) {
         let tcx = self.tcx;
-
         let path_segs = match res {
             Res::Local(_) | Res::SelfCtor(_) => vec![],
             Res::Def(kind, def_id) => <dyn AstConv<'_>>::def_ids_for_value_path_segments(

compiler/rustc_hir_typeck/src/method/suggest.rs

@@ -5,6 +5,7 @@ use crate::errors;
 use crate::FnCtxt;
 use rustc_ast::ast::Mutability;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_errors::StashKey;
 use rustc_errors::{
     pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed,
     MultiSpan,
@@ -13,6 +14,8 @@ use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::DefId;
 use rustc_hir::lang_items::LangItem;
+use rustc_hir::PatKind::Binding;
+use rustc_hir::PathSegment;
 use rustc_hir::{ExprKind, Node, QPath};
 use rustc_infer::infer::{
     type_variable::{TypeVariableOrigin, TypeVariableOriginKind},
@@ -35,11 +38,11 @@ use rustc_trait_selection::traits::{
     FulfillmentError, Obligation, ObligationCause, ObligationCauseCode,
 };
 
-use std::cmp::Ordering;
-use std::iter;
-
 use super::probe::{AutorefOrPtrAdjustment, IsSuggestion, Mode, ProbeScope};
 use super::{CandidateSource, MethodError, NoMatchData};
+use rustc_hir::intravisit::Visitor;
+use std::cmp::Ordering;
+use std::iter;
 
 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     fn is_fn_ty(&self, ty: Ty<'tcx>, span: Span) -> bool {
@@ -1470,6 +1473,60 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         false
     }
 
+    /// For code `rect::area(...)`,
+    /// if `rect` is a local variable and `area` is a valid assoc method for it,
+    /// we try to suggest `rect.area()`
+    pub(crate) fn suggest_assoc_method_call(&self, segs: &[PathSegment<'_>]) {
+        debug!("suggest_assoc_method_call segs: {:?}", segs);
+        if segs.len() != 2 {
+            return;
+        }
+        let (seg1, seg2) = (&segs[0], &segs[1]);
+        let Some(mut diag) =
+                self.tcx.sess.diagnostic().steal_diagnostic(seg1.ident.span, StashKey::CallAssocMethod)
+                else { return };
+
+        let map = self.infcx.tcx.hir();
+        let body_id = map.body_owned_by(seg1.hir_id.owner.def_id);
+        let body = map.body(body_id);
+        struct LetVisitor<'a> {
+            result: Option<&'a hir::Expr<'a>>,
+            ident_name: Symbol,
+        }
+
+        impl<'v> Visitor<'v> for LetVisitor<'v> {
+            fn visit_stmt(&mut self, ex: &'v hir::Stmt<'v>) {
+                if let hir::StmtKind::Local(hir::Local { pat, init, .. }) = &ex.kind {
+                    if let Binding(_, _, ident, ..) = pat.kind &&
+                        ident.name == self.ident_name {
+                        self.result = *init;
+                    }
+                }
+                hir::intravisit::walk_stmt(self, ex);
+            }
+        }
+
+        let mut visitor = LetVisitor { result: None, ident_name: seg1.ident.name };
+        visitor.visit_body(&body);
+
+        let parent = self.tcx.hir().get_parent_node(seg1.hir_id);
+        if let Some(Node::Expr(call_expr)) = self.tcx.hir().find(parent) &&
+            let Some(expr) = visitor.result {
+            let self_ty = self.check_expr(expr);
+            let probe = self.lookup_probe(
+                seg2.ident,
+                self_ty,
+                call_expr,
+                ProbeScope::TraitsInScope,
+            );
+            if probe.is_ok() {
+                diag.emit();
+                return;
+            }
+        }
+        diag.cancel();
+    }
+
     /// Suggest calling a method on a field i.e. `a.field.bar()` instead of `a.bar()`
     fn suggest_calling_method_on_field(
         &self,

compiler/rustc_resolve/src/diagnostics.rs

@@ -1840,13 +1840,20 @@ impl<'a> Resolver<'a> {
 
             (format!("use of undeclared type `{}`", ident), suggestion)
         } else {
-            let suggestion = if ident.name == sym::alloc {
-                Some((
+            // crate or module resolve failed, here we try three things:
+
+            // 1. special handling for `alloc`
+            let mut suggestion = None;
+            if ident.name == sym::alloc {
+                suggestion = Some((
                     vec![],
                     String::from("add `extern crate alloc` to use the `alloc` crate"),
                     Applicability::MaybeIncorrect,
                 ))
-            } else {
+            }
+
+            // 2. check whether there is a similar name
+            suggestion = suggestion.or_else(|| {
                 self.find_similarly_named_module_or_crate(ident.name, &parent_scope.module).map(
                     |sugg| {
                         (
@@ -1856,7 +1863,56 @@ impl<'a> Resolver<'a> {
                         )
                     },
                 )
-            };
+            });
+
+            // 3. check whether the name refers to an item in local scope
+            // then delay to check whether methond name is an associated function or not
+            // For example:
+            // ```
+            // struct Foo;
+            // impl Foo {
+            //    fn bar(&self) {}
+            // }
+            //
+            // fn main() {
+            //    let foo = Foo {};
+            //    foo::bar(); // suggest to foo.bar();
+            //}
+            //```
+            if suggestion.is_none() &&
+                let Some(ribs) = ribs &&
+                let Some(LexicalScopeBinding::Res(Res::Local(local_id))) = self.resolve_ident_in_lexical_scope(
+                    ident,
+                    ValueNS,
+                    parent_scope,
+                    None,
+                    &ribs[ValueNS],
+                    ignore_binding,
+                )
+                {
+                    let sm = self.session.source_map();
+                    // only check path with two segments, like `foo::bar(..)`
+                    if let Ok(span) = sm.span_extend_while(ident.span.shrink_to_hi(), |c| c != ' ') &&
+                        let Ok(snippet) = sm.span_to_snippet(span) &&
+                            snippet.starts_with("::") &&  snippet.matches("::").count() == 1 {
+                        let local_span = *self.pat_span_map.get(&local_id).unwrap();
+                        let mut err = self.session.struct_span_err(
+                            ident.span,
+                            format!(
+                                "`{}` is not a crate or module",
+                                ident
+                            )
+                        );
+                        err.span_suggestion_verbose(
+                            sm.span_extend_while(ident.span.shrink_to_hi(), |c| c == ':').unwrap(),
+                            "maybe you meant to call instance method",
+                            ".".to_string(),
+                            Applicability::MaybeIncorrect
+                        );
+                        err.span_warn(local_span, format!("ident `{}` is defined at here", ident));
+                        err.stash(ident.span, rustc_errors::StashKey::CallAssocMethod);
+                    }
+                };
             (format!("use of undeclared crate or module `{}`", ident), suggestion)
         }
     }

src/test/ui/resolve/issue-101749-2.rs

@@ -0,0 +1,16 @@
+struct Rectangle {
+    width: i32,
+    height: i32,
+}
+impl Rectangle {
+    fn new(width: i32, height: i32) -> Self {
+        Self { width, height }
+    }
+}
+
+fn main() {
+    let rect = Rectangle::new(3, 4);
+    // `area` is not implemented for `Rectangle`, so this should not suggest
+    let _ = rect::area();
+    //~^ ERROR failed to resolve: use of undeclared crate or module `rect`
+}

src/test/ui/resolve/issue-101749-2.stderr

@@ -0,0 +1,9 @@
+error[E0433]: failed to resolve: use of undeclared crate or module `rect`
+  --> $DIR/issue-101749-2.rs:14:13
+   |
+LL |     let _ = rect::area();
+   |             ^^^^ use of undeclared crate or module `rect`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0433`.

src/test/ui/resolve/issue-101749.fixed

@@ -0,0 +1,21 @@
+// run-rustfix
+struct Rectangle {
+    width: i32,
+    height: i32,
+}
+impl Rectangle {
+    fn new(width: i32, height: i32) -> Self {
+        Self { width, height }
+    }
+    fn area(&self) -> i32 {
+        self.height * self.width
+    }
+}
+
+fn main() {
+    let rect = Rectangle::new(3, 4);
+    //~^ WARNING ident `rect` is defined at here
+    let _ = rect.area();
+    //~^ ERROR failed to resolve: use of undeclared crate or module `rect`
+    //~| ERROR `rect` is not a crate or module
+}

src/test/ui/resolve/issue-101749.rs

@@ -0,0 +1,21 @@
+// run-rustfix
+struct Rectangle {
+    width: i32,
+    height: i32,
+}
+impl Rectangle {
+    fn new(width: i32, height: i32) -> Self {
+        Self { width, height }
+    }
+    fn area(&self) -> i32 {
+        self.height * self.width
+    }
+}
+
+fn main() {
+    let rect = Rectangle::new(3, 4);
+    //~^ WARNING ident `rect` is defined at here
+    let _ = rect::area();
+    //~^ ERROR failed to resolve: use of undeclared crate or module `rect`
+    //~| ERROR `rect` is not a crate or module
+}

src/test/ui/resolve/issue-101749.stderr

@@ -0,0 +1,25 @@
+error[E0433]: failed to resolve: use of undeclared crate or module `rect`
+  --> $DIR/issue-101749.rs:18:13
+   |
+LL |     let _ = rect::area();
+   |             ^^^^ use of undeclared crate or module `rect`
+
+error: `rect` is not a crate or module
+  --> $DIR/issue-101749.rs:18:13
+   |
+LL |     let _ = rect::area();
+   |             ^^^^
+   |
+warning: ident `rect` is defined at here
+  --> $DIR/issue-101749.rs:16:9
+   |
+LL |     let rect = Rectangle::new(3, 4);
+   |         ^^^^
+help: maybe you meant to call instance method
+   |
+LL |     let _ = rect.area();
+   |                 ~
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0433`.