Auto merge of #32358 - Manishearth:pr-32053, r=Manishearth

Add note if method is called on a function object

rebase of #32053

src/librustc_typeck/check/method/suggest.rs

@@ -25,11 +25,13 @@ use middle::subst::Substs;
 use middle::traits::{Obligation, SelectionContext};
 use util::nodemap::{FnvHashSet};
 
+
 use syntax::ast;
 use syntax::codemap::Span;
 use syntax::errors::DiagnosticBuilder;
 use rustc_front::print::pprust;
 use rustc_front::hir;
+use rustc_front::hir::Expr_;
 
 use std::cell;
 use std::cmp::Ordering;
@@ -37,6 +39,42 @@ use std::cmp::Ordering;
 use super::{MethodError, NoMatchData, CandidateSource, impl_item, trait_item};
 use super::probe::Mode;
 
+fn is_fn_ty<'a, 'tcx>(ty: &Ty<'tcx>, fcx: &FnCtxt<'a, 'tcx>, span: Span) -> bool {
+    let cx = fcx.tcx();
+    println!("{:?}", ty);
+    match ty.sty {
+        // Not all of these (e.g. unsafe fns) implement FnOnce
+        // so we look for these beforehand
+        ty::TyClosure(..) | ty::TyFnDef(..) | ty::TyFnPtr(_) => true,
+        // If it's not a simple function, look for things which implement FnOnce
+        _ => {
+            if let Ok(fn_once_trait_did) =
+                    cx.lang_items.require(FnOnceTraitLangItem) {
+                let infcx = fcx.infcx();
+                infcx.probe(|_| {
+                    let fn_once_substs =
+                        Substs::new_trait(vec![infcx.next_ty_var()],
+                                          Vec::new(),
+                                          ty);
+                    let trait_ref =
+                      ty::TraitRef::new(fn_once_trait_did,
+                                        cx.mk_substs(fn_once_substs));
+                    let poly_trait_ref = trait_ref.to_poly_trait_ref();
+                    let obligation = Obligation::misc(span,
+                                                      fcx.body_id,
+                                                      poly_trait_ref
+                                                         .to_predicate());
+                    let mut selcx = SelectionContext::new(infcx);
+
+                    return selcx.evaluate_obligation(&obligation)
+                })
+            } else {
+                false
+            }
+        }
+    }
+}
+
 pub fn report_error<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
                               span: Span,
                               rcvr_ty: Ty<'tcx>,
@@ -79,60 +117,41 @@ pub fn report_error<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
                                         // snippet
                     };
 
-                    macro_rules! span_stored_function {
-                        () => {
-                            err.span_note(span,
-                                          &format!("use `({0}.{1})(...)` if you meant to call \
-                                                    the function stored in the `{1}` field",
-                                                   expr_string, item_name));
-                        }
-                    }
-
-                    macro_rules! span_did_you_mean {
-                        () => {
-                            err.span_note(span, &format!("did you mean to write `{0}.{1}`?",
-                                                         expr_string, item_name));
-                        }
-                    }
-
-                    // Determine if the field can be used as a function in some way
                     let field_ty = field.ty(cx, substs);
 
-                    match field_ty.sty {
+                    if is_fn_ty(&field_ty, &fcx, span) {
-                        // Not all of these (e.g. unsafe fns) implement FnOnce
+                        err.span_note(span,
-                        // so we look for these beforehand
+                                      &format!("use `({0}.{1})(...)` if you meant to call \
-                        ty::TyClosure(..) | ty::TyFnDef(..) | ty::TyFnPtr(_) => {
+                                               the function stored in the `{1}` field",
-                            span_stored_function!();
+                                               expr_string, item_name));
-                        }
+                    } else {
-                        // If it's not a simple function, look for things which implement FnOnce
+                        err.span_note(span, &format!("did you mean to write `{0}.{1}`?",
-                        _ => {
+                                                     expr_string, item_name));
-                            if let Ok(fn_once_trait_did) =
+                    }
-                                    cx.lang_items.require(FnOnceTraitLangItem) {
+                }
-                                let infcx = fcx.infcx();
+            }
-                                infcx.probe(|_| {
-                                    let fn_once_substs =
-                                        Substs::new_trait(vec![infcx.next_ty_var()],
-                                                          Vec::new(),
-                                                          field_ty);
-                                    let trait_ref =
-                                      ty::TraitRef::new(fn_once_trait_did,
-                                                        cx.mk_substs(fn_once_substs));
-                                    let poly_trait_ref = trait_ref.to_poly_trait_ref();
-                                    let obligation = Obligation::misc(span,
-                                                                      fcx.body_id,
-                                                                      poly_trait_ref
-                                                                         .to_predicate());
-                                    let mut selcx = SelectionContext::new(infcx);
 
-                                    if selcx.evaluate_obligation(&obligation) {
+            if is_fn_ty(&rcvr_ty, &fcx, span) {
-                                        span_stored_function!();
+                macro_rules! report_function {
-                                    } else {
+                    ($span:expr, $name:expr) => {
-                                        span_did_you_mean!();
+                        err.fileline_note(
-                                    }
+                            $span,
-                                });
+                            &format!("{} is a function, perhaps you wish to call it",
-                            } else {
+                                     $name));
-                                span_did_you_mean!();
+                    }
-                            }
+                }
+
+                if let Some(expr) = rcvr_expr {
+                    if let Ok (expr_string) = cx.sess.codemap().span_to_snippet(expr.span) {
+                        report_function!(expr.span, expr_string);
+                        err.span_suggestion(expr.span,
+                                            "try calling the base function:",
+                                            format!("{}()",
+                                                    expr_string));
+                    }
+                    else if let Expr_::ExprPath(_, path) = expr.node.clone() {
+                        if let Some(segment) = path.segments.last() {
+                            report_function!(expr.span, segment.identifier.name);
                         }
                     }
                 }

src/test/compile-fail/issue-29124.rs

@@ -0,0 +1,35 @@
+// Copyright 2015 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 ret;
+struct obj;
+
+impl obj {
+    fn func() -> ret {
+        ret
+    }
+}
+
+fn func() -> ret {
+    ret
+}
+
+fn main() {
+    obj::func.x();
+    //~^ ERROR no method named `x` found for type `fn() -> ret {obj::func}` in the current scope
+    //~^^ NOTE obj::func is a function, perhaps you wish to call it
+    //~^^^ HELP try calling the base function:
+    //~| SUGGESTION obj::func().x();
+    func.x();
+    //~^ ERROR no method named `x` found for type `fn() -> ret {func}` in the current scope
+    //~^^ NOTE func is a function, perhaps you wish to call it
+    //~^^^ HELP try calling the base function:
+    //~| SUGGESTION func().x();
+}