Auto merge of #43270 - petrochenkov:fixstab, r=alexcrichton

[rust.git] / src / librustc_typeck / check / demand.rs

diff --git a/src/librustc_typeck/check/demand.rs b/src/librustc_typeck/check/demand.rs
index 1b6f96cf65137f3fcda3d25d2822d2a4c7986a6f..828106df7821b2e1b435c295b4b3a40c471d36c4 100644 (file)
--- a/src/librustc_typeck/check/demand.rs
+++ b/src/librustc_typeck/check/demand.rs
@@ -16,6 +16,7 @@
 use syntax::ast;
 use syntax_pos::{self, Span};
 use rustc::hir;
+use rustc::hir::print;
 use rustc::hir::def::Def;
 use rustc::ty::{self, Ty, AssociatedItem};
 use errors::{DiagnosticBuilder, CodeMapper};
@@ -73,21 +74,55 @@ pub fn demand_eqtype_with_origin(&self,
         }
     }
 
+    pub fn demand_coerce(&self, expr: &hir::Expr, checked_ty: Ty<'tcx>, expected: Ty<'tcx>) {
+        if let Some(mut err) = self.demand_coerce_diag(expr, checked_ty, expected) {
+            err.emit();
+        }
+    }
+
     // Checks that the type of `expr` can be coerced to `expected`.
     //
     // NB: This code relies on `self.diverges` to be accurate.  In
     // particular, assignments to `!` will be permitted if the
     // diverges flag is currently "always".
-    pub fn demand_coerce(&self,
-                         expr: &hir::Expr,
-                         checked_ty: Ty<'tcx>,
-                         expected: Ty<'tcx>) {
+    pub fn demand_coerce_diag(&self,
+                              expr: &hir::Expr,
+                              checked_ty: Ty<'tcx>,
+                              expected: Ty<'tcx>) -> Option<DiagnosticBuilder<'tcx>> {
         let expected = self.resolve_type_vars_with_obligations(expected);
 
         if let Err(e) = self.try_coerce(expr, checked_ty, self.diverges.get(), expected) {
             let cause = self.misc(expr.span);
             let expr_ty = self.resolve_type_vars_with_obligations(checked_ty);
             let mut err = self.report_mismatched_types(&cause, expected, expr_ty, e);
+
+            // If the expected type is an enum with any variants whose sole
+            // field is of the found type, suggest such variants. See Issue
+            // #42764.
+            if let ty::TyAdt(expected_adt, substs) = expected.sty {
+                let mut compatible_variants = vec![];
+                for variant in &expected_adt.variants {
+                    if variant.fields.len() == 1 {
+                        let sole_field = &variant.fields[0];
+                        let sole_field_ty = sole_field.ty(self.tcx, substs);
+                        if self.can_coerce(expr_ty, sole_field_ty) {
+                            let mut variant_path = self.tcx.item_path_str(variant.did);
+                            variant_path = variant_path.trim_left_matches("std::prelude::v1::")
+                                .to_string();
+                            compatible_variants.push(variant_path);
+                        }
+                    }
+                }
+                if !compatible_variants.is_empty() {
+                    let expr_text = print::to_string(print::NO_ANN, |s| s.print_expr(expr));
+                    let suggestions = compatible_variants.iter()
+                        .map(|v| format!("{}({})", v, expr_text)).collect::<Vec<_>>();
+                    err.span_suggestions(expr.span,
+                                         "perhaps you meant to use a variant of the expected type",
+                                         suggestions);
+                }
+            }
+
             if let Some(suggestion) = self.check_ref(expr,
                                                      checked_ty,
                                                      expected) {
@@ -105,8 +140,9 @@ pub fn demand_coerce(&self,
                                       self.get_best_match(&suggestions).join("\n")));
                 }
             }
-            err.emit();
+            return Some(err);
         }
+        None
     }
 
     fn format_method_suggestion(&self, method: &AssociatedItem) -> String {
@@ -143,12 +179,7 @@ fn get_best_match(&self, methods: &[AssociatedItem]) -> Vec<String> {
     fn has_no_input_arg(&self, method: &AssociatedItem) -> bool {
         match method.def() {
             Def::Method(def_id) => {
-                match self.tcx.type_of(def_id).sty {
-                    ty::TypeVariants::TyFnDef(_, _, sig) => {
-                        sig.inputs().skip_binder().len() == 1
-                    }
-                    _ => false,
-                }
+                self.tcx.fn_sig(def_id).inputs().skip_binder().len() == 1
             }
             _ => false,
         }