Shrink span to variant discriminant expression for E0081

Author: KiChjang

src/librustc_typeck/check/mod.rs

@@ -1272,13 +1272,21 @@ pub fn check_enum_variants<'a,'tcx>(ccx: &CrateCtxt<'a,'tcx>,
 
             // Check for duplicate discriminant values
             if let Some(i) = disr_vals.iter().position(|&x| x == current_disr_val) {
-                let mut err = struct_span_err!(ccx.tcx.sess, v.span, E0081,
-                    "discriminant value `{}` already exists", disr_vals[i]);
                 let variant_i_node_id = ccx.tcx.map.as_local_node_id(variants[i].did).unwrap();
-                err.span_label(ccx.tcx.map.span(variant_i_node_id),
-                               &format!("first use of `{}`", disr_vals[i]));
-                err.span_label(v.span , &format!("enum already has `{}`", disr_vals[i]));
-                err.emit();
+                let variant_i = ccx.tcx.map.expect_variant(variant_i_node_id);
+                let i_span = match variant_i.node.disr_expr {
+                    Some(ref expr) => expr.span,
+                    None => ccx.tcx.map.span(variant_i_node_id)
+                };
+                let span = match v.node.disr_expr {
+                    Some(ref expr) => expr.span,
+                    None => v.span
+                };
+                struct_span_err!(ccx.tcx.sess, span, E0081,
+                                 "discriminant value `{}` already exists", disr_vals[i])
+                    .span_label(i_span, &format!("first use of `{}`", disr_vals[i]))
+                    .span_label(span , &format!("enum already has `{}`", disr_vals[i]))
+                    .emit();
             }
             disr_vals.push(current_disr_val);
         }

src/test/compile-fail/E0081.rs

@@ -9,8 +9,10 @@
 // except according to those terms.
 
 enum Enum {
-    P = 3,
-    X = 3, //~ ERROR E0081
+    P = 3, //~ NOTE first use of `3isize`
+    X = 3,
+    //~^ ERROR discriminant value `3isize` already exists
+    //~| NOTE enum already has `3isize`
     Y = 5
 }
 

src/test/compile-fail/issue-15524.rs

@@ -12,17 +12,20 @@ const N: isize = 1;
 
 enum Foo {
     A = 1,
-    //~^ NOTE first use
-    //~| NOTE first use
-    //~| NOTE first use
-    B = 1, //~ ERROR discriminant value
-    //~^ NOTE enum already
+    //~^ NOTE first use of `1isize`
+    //~| NOTE first use of `1isize`
+    //~| NOTE first use of `1isize`
+    B = 1,
+    //~^ ERROR discriminant value `1isize` already exists
+    //~| NOTE enum already has `1isize`
     C = 0,
-    D, //~ ERROR discriminant value
-    //~^ NOTE enum already
+    D,
+    //~^ ERROR discriminant value `1isize` already exists
+    //~| NOTE enum already has `1isize`
 
-    E = N, //~ ERROR discriminant value
-    //~^ NOTE enum already
+    E = N,
+    //~^ ERROR discriminant value `1isize` already exists
+    //~| NOTE enum already has `1isize`
 
 }