Most specific method in diagnostic generation for overload resolution

[B. Blaser]

Hi,

Related to [1], I wrote a specialized map to store only the most
specific candidates during the diagnostic generation for overload
resolution, here under.

It's then used in "Resolve.InapplicableSymbolsError.mapCandidates()"
when non-applicable methods are collected to generate the diagnostic.

What do you think?
Bernard

[1] http://mail.openjdk.java.net/pipermail/compiler-dev/2017-September/011062.html

diff --git a/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Resolve.java
b/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Resolve.java
--- a/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Resolve.java
+++ b/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Resolve.java
@@ -59,6 +59,7 @@
 import java.util.HashSet;
 import java.util.Iterator;
 import java.util.LinkedHashMap;
+import java.util.LinkedList;
 import java.util.Map;
 import java.util.Set;
 import java.util.function.BiFunction;
@@ -3995,14 +3996,29 @@
         }
         //where
             private Map<Symbol, JCDiagnostic> mapCandidates() {
-                Map<Symbol, JCDiagnostic> candidates = new LinkedHashMap<>();
+                MostSpecificMap candidates = new MostSpecificMap();
                 for (Candidate c : resolveContext.candidates) {
                     if (c.isApplicable()) continue;
-                    candidates.put(c.sym, c.details);
+                    candidates.put(c);
                 }
                 return candidates;
             }

+            @SuppressWarnings("serial")
+            private class MostSpecificMap extends
LinkedHashMap<Symbol, JCDiagnostic> {
+                private void put(Candidate c) {
+                    new LinkedList<>(keySet()).stream()
+                            .filter( s -> !s.equals(c.sym) )
+                            .filter( s -> c.sym.overrides(s,
(TypeSymbol)s.owner, types, false) )
+                            .forEach( s -> remove(s) );
+
+                    if (!keySet().stream()
+                            .filter( s -> !s.equals(c.sym) )
+                            .anyMatch( s -> s.overrides(c.sym,
(TypeSymbol)c.sym.owner, types, false) ))
+                        put(c.sym, c.details);
+                }
+            }
+
             Map<Symbol, JCDiagnostic> filterCandidates(Map<Symbol,
JCDiagnostic> candidatesMap) {
                 Map<Symbol, JCDiagnostic> candidates = new LinkedHashMap<>();
                 for (Map.Entry<Symbol, JCDiagnostic> _entry :
candidatesMap.entrySet()) {