Rollup merge of #75509 - estebank:coming-merrily-from-java-land, r=lcnr

Tweak suggestion for `this` -> `self`

* When referring to `this` in associated `fn`s always suggest `self`.
* Point at ident for `fn` lacking `self`
* Suggest adding `self` to assoc `fn`s when appropriate

_Improvements based on the narrative in https://fasterthanli.me/articles/i-am-a-java-csharp-c-or-cplusplus-dev-time-to-do-some-rust_

src/librustc_ast/visit.rs

@@ -50,6 +50,13 @@ impl<'a> FnKind<'a> {
         }
     }
 
+    pub fn ident(&self) -> Option<&Ident> {
+        match self {
+            FnKind::Fn(_, ident, ..) => Some(ident),
+            _ => None,
+        }
+    }
+
     pub fn decl(&self) -> &'a FnDecl {
         match self {
             FnKind::Fn(_, _, sig, _, _) => &sig.decl,

src/librustc_resolve/late/diagnostics.rs

@@ -7,6 +7,7 @@ use crate::{PathResult, PathSource, Segment};
 
 use rustc_ast::ast::{self, Expr, ExprKind, Item, ItemKind, NodeId, Path, Ty, TyKind};
 use rustc_ast::util::lev_distance::find_best_match_for_name;
+use rustc_ast::visit::FnKind;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder};
 use rustc_hir as hir;
@@ -175,16 +176,40 @@ impl<'a> LateResolutionVisitor<'a, '_, '_> {
         let code = source.error_code(res.is_some());
         let mut err = self.r.session.struct_span_err_with_code(base_span, &base_msg, code);
 
+        let is_assoc_fn = self.self_type_is_available(span);
         // Emit help message for fake-self from other languages (e.g., `this` in Javascript).
-        if ["this", "my"].contains(&&*item_str.as_str())
-            && self.self_value_is_available(path[0].ident.span, span)
-        {
+        if ["this", "my"].contains(&&*item_str.as_str()) && is_assoc_fn {
             err.span_suggestion_short(
                 span,
                 "you might have meant to use `self` here instead",
                 "self".to_string(),
                 Applicability::MaybeIncorrect,
             );
+            if !self.self_value_is_available(path[0].ident.span, span) {
+                if let Some((FnKind::Fn(_, _, sig, ..), fn_span)) =
+                    &self.diagnostic_metadata.current_function
+                {
+                    let (span, sugg) = if let Some(param) = sig.decl.inputs.get(0) {
+                        (param.span.shrink_to_lo(), "&self, ")
+                    } else {
+                        (
+                            self.r
+                                .session
+                                .source_map()
+                                .span_through_char(*fn_span, '(')
+                                .shrink_to_hi(),
+                            "&self",
+                        )
+                    };
+                    err.span_suggestion_verbose(
+                        span,
+                        "if you meant to use `self`, you are also missing a `self` receiver \
+                         argument",
+                        sugg.to_string(),
+                        Applicability::MaybeIncorrect,
+                    );
+                }
+            }
         }
 
         // Emit special messages for unresolved `Self` and `self`.
@@ -213,7 +238,38 @@ impl<'a> LateResolutionVisitor<'a, '_, '_> {
                 if fn_kind.decl().inputs.get(0).map(|p| p.is_self()).unwrap_or(false) {
                     err.span_label(*span, "this function has a `self` parameter, but a macro invocation can only access identifiers it receives from parameters");
                 } else {
-                    err.span_label(*span, "this function doesn't have a `self` parameter");
+                    let doesnt = if is_assoc_fn {
+                        let (span, sugg) = fn_kind
+                            .decl()
+                            .inputs
+                            .get(0)
+                            .map(|p| (p.span.shrink_to_lo(), "&self, "))
+                            .unwrap_or_else(|| {
+                                (
+                                    self.r
+                                        .session
+                                        .source_map()
+                                        .span_through_char(*span, '(')
+                                        .shrink_to_hi(),
+                                    "&self",
+                                )
+                            });
+                        err.span_suggestion_verbose(
+                            span,
+                            "add a `self` receiver parameter to make the associated `fn` a method",
+                            sugg.to_string(),
+                            Applicability::MaybeIncorrect,
+                        );
+                        "doesn't"
+                    } else {
+                        "can't"
+                    };
+                    if let Some(ident) = fn_kind.ident() {
+                        err.span_label(
+                            ident.span,
+                            &format!("this function {} have a `self` parameter", doesnt),
+                        );
+                    }
                 }
             }
             return (err, Vec::new());

src/test/ui/error-codes/E0424.rs

@@ -6,6 +6,10 @@ impl Foo {
     fn foo() {
         self.bar(); //~ ERROR E0424
     }
+
+    fn baz(_: i32) {
+        self.bar(); //~ ERROR E0424
+    }
 }
 
 fn main () {

src/test/ui/error-codes/E0424.stderr

@@ -1,21 +1,37 @@
 error[E0424]: expected value, found module `self`
   --> $DIR/E0424.rs:7:9
    |
-LL | /     fn foo() {
-LL | |         self.bar();
-   | |         ^^^^ `self` value is a keyword only available in methods with a `self` parameter
-LL | |     }
-   | |_____- this function doesn't have a `self` parameter
+LL |     fn foo() {
+   |        --- this function doesn't have a `self` parameter
+LL |         self.bar();
+   |         ^^^^ `self` value is a keyword only available in methods with a `self` parameter
+   |
+help: add a `self` receiver parameter to make the associated `fn` a method
+   |
+LL |     fn foo(&self) {
+   |            ^^^^^
+
+error[E0424]: expected value, found module `self`
+  --> $DIR/E0424.rs:11:9
+   |
+LL |     fn baz(_: i32) {
+   |        --- this function doesn't have a `self` parameter
+LL |         self.bar();
+   |         ^^^^ `self` value is a keyword only available in methods with a `self` parameter
+   |
+help: add a `self` receiver parameter to make the associated `fn` a method
+   |
+LL |     fn baz(&self, _: i32) {
+   |            ^^^^^^
 
 error[E0424]: expected unit struct, unit variant or constant, found module `self`
-  --> $DIR/E0424.rs:12:9
+  --> $DIR/E0424.rs:16:9
    |
-LL | / fn main () {
-LL | |     let self = "self";
-   | |         ^^^^ `self` value is a keyword and may not be bound to variables or shadowed
-LL | | }
-   | |_- this function doesn't have a `self` parameter
+LL | fn main () {
+   |    ---- this function can't have a `self` parameter
+LL |     let self = "self";
+   |         ^^^^ `self` value is a keyword and may not be bound to variables or shadowed
 
-error: aborting due to 2 previous errors
+error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0424`.

src/test/ui/issues/issue-5099.rs

@@ -1,3 +1,10 @@
-trait B < A > { fn a() -> A { this.a } } //~ ERROR cannot find value `this` in this scope
+trait B <A> {
+    fn a() -> A {
+        this.a //~ ERROR cannot find value `this` in this scope
+    }
+    fn b(x: i32) {
+        this.b(x); //~ ERROR cannot find value `this` in this scope
+    }
+}
 
 fn main() {}

src/test/ui/issues/issue-5099.stderr

@@ -1,9 +1,33 @@
 error[E0425]: cannot find value `this` in this scope
-  --> $DIR/issue-5099.rs:1:31
+  --> $DIR/issue-5099.rs:3:9
    |
-LL | trait B < A > { fn a() -> A { this.a } }
-   |                               ^^^^ not found in this scope
+LL |         this.a
+   |         ^^^^ not found in this scope
+   |
+help: you might have meant to use `self` here instead
+   |
+LL |         self.a
+   |         ^^^^
+help: if you meant to use `self`, you are also missing a `self` receiver argument
+   |
+LL |     fn a(&self) -> A {
+   |          ^^^^^
+
+error[E0425]: cannot find value `this` in this scope
+  --> $DIR/issue-5099.rs:6:9
+   |
+LL |         this.b(x);
+   |         ^^^^ not found in this scope
+   |
+help: you might have meant to use `self` here instead
+   |
+LL |         self.b(x);
+   |         ^^^^
+help: if you meant to use `self`, you are also missing a `self` receiver argument
+   |
+LL |     fn b(&self, x: i32) {
+   |          ^^^^^^
 
-error: aborting due to previous error
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0425`.

src/test/ui/resolve/issue-2356.stderr

@@ -70,14 +70,15 @@ LL |         purr();
 error[E0424]: expected value, found module `self`
   --> $DIR/issue-2356.rs:65:8
    |
-LL | /   fn meow() {
-LL | |     if self.whiskers > 3 {
-   | |        ^^^^ `self` value is a keyword only available in methods with a `self` parameter
-LL | |
-LL | |         println!("MEOW");
-LL | |     }
-LL | |   }
-   | |___- this function doesn't have a `self` parameter
+LL |   fn meow() {
+   |      ---- this function doesn't have a `self` parameter
+LL |     if self.whiskers > 3 {
+   |        ^^^^ `self` value is a keyword only available in methods with a `self` parameter
+   |
+help: add a `self` receiver parameter to make the associated `fn` a method
+   |
+LL |   fn meow(&self) {
+   |           ^^^^^
 
 error[E0425]: cannot find function `grow_older` in this scope
   --> $DIR/issue-2356.rs:72:5
@@ -112,12 +113,10 @@ LL |     purr_louder();
 error[E0424]: expected value, found module `self`
   --> $DIR/issue-2356.rs:92:5
    |
-LL | / fn main() {
-LL | |     self += 1;
-   | |     ^^^^ `self` value is a keyword only available in methods with a `self` parameter
-LL | |
-LL | | }
-   | |_- this function doesn't have a `self` parameter
+LL | fn main() {
+   |    ---- this function can't have a `self` parameter
+LL |     self += 1;
+   |     ^^^^ `self` value is a keyword only available in methods with a `self` parameter
 
 error: aborting due to 17 previous errors