Auto merge of #54694 - csmoe:self_this, r=estebank

Suggest to use self for fake-self from other languages

Closes #54019
r? @estebank

src/librustc_resolve/lib.rs

@@ -2968,13 +2968,13 @@ impl<'a, 'crateloader: 'a> Resolver<'a, 'crateloader> {
             // Make the base error.
             let expected = source.descr_expected();
             let path_str = names_to_string(path);
+            let item_str = path[path.len() - 1];
             let code = source.error_code(def.is_some());
             let (base_msg, fallback_label, base_span) = if let Some(def) = def {
                 (format!("expected {}, found {} `{}`", expected, def.kind_name(), path_str),
                  format!("not a {}", expected),
                  span)
             } else {
-                let item_str = path[path.len() - 1];
                 let item_span = path[path.len() - 1].span;
                 let (mod_prefix, mod_str) = if path.len() == 1 {
                     (String::new(), "this scope".to_string())
@@ -2997,6 +2997,20 @@ impl<'a, 'crateloader: 'a> Resolver<'a, 'crateloader> {
             let code = DiagnosticId::Error(code.into());
             let mut err = this.session.struct_span_err_with_code(base_span, &base_msg, code);
 
+            // Emit help message for fake-self from other languages like `this`(javascript)
+            let fake_self: Vec<Ident> = ["this", "my"].iter().map(
+                |s| Ident::from_str(*s)
+            ).collect();
+            if fake_self.contains(&item_str)
+                && this.self_value_is_available(path[0].span, span) {
+                err.span_suggestion_with_applicability(
+                    span,
+                    "did you mean",
+                    "self".to_string(),
+                    Applicability::MaybeIncorrect,
+                );
+            }
+
             // Emit special messages for unresolved `Self` and `self`.
             if is_self_type(path, ns) {
                 __diagnostic_used!(E0411);

src/test/ui/self/suggest-self.rs

@@ -0,0 +1,52 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+struct Foo {
+    x: i32,
+}
+
+impl Foo {
+    fn this1(&self) -> i32 {
+        let this = self;
+        let a = 1;
+        this.x
+    }
+
+    fn this2(&self) -> i32 {
+        let a = Foo {
+            x: 2
+        };
+        let this = a;
+        this.x
+    }
+
+    fn foo(&self) -> i32 {
+        this.x
+        //~^ ERROR cannot find value `this` in this scope
+    }
+
+    fn bar(&self) -> i32 {
+        this.foo()
+        //~^ ERROR cannot find value `this` in this scope
+    }
+
+    fn baz(&self) -> i32 {
+        my.bar()
+        //~^ ERROR cannot find value `my` in this scope
+    }
+}
+
+fn main() {
+    let this = vec![1, 2, 3];
+    let my = vec![1, 2, 3];
+    let len = this.len();
+    let len = my.len();
+}
+

src/test/ui/self/suggest-self.stderr

@@ -0,0 +1,30 @@
+error[E0425]: cannot find value `this` in this scope
+  --> $DIR/suggest-self.rs:31:9
+   |
+LL |         this.x
+   |         ^^^^
+   |         |
+   |         not found in this scope
+   |         help: did you mean: `self`
+
+error[E0425]: cannot find value `this` in this scope
+  --> $DIR/suggest-self.rs:36:9
+   |
+LL |         this.foo()
+   |         ^^^^
+   |         |
+   |         not found in this scope
+   |         help: did you mean: `self`
+
+error[E0425]: cannot find value `my` in this scope
+  --> $DIR/suggest-self.rs:41:9
+   |
+LL |         my.bar()
+   |         ^^
+   |         |
+   |         not found in this scope
+   |         help: did you mean: `self`
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0425`.