Prevent duplicate rule metadata in /errorlog

src/Compilers/Core/CodeAnalysisTest/Diagnostics/ErrorLoggerTests.cs

@@ -93,10 +93,25 @@ public void AdditionalLocationsAsRelatedLocations()
         public void DescriptorIdCollision()
         {
             var descriptors = new[] {
+                // Toughest case: generation of TST001.001 collides with with actual TST001.001 and must be bumped to TST00.002
                 new DiagnosticDescriptor("TST001.001",    "_TST001.001_",     "", "", DiagnosticSeverity.Warning, true),
                 new DiagnosticDescriptor("TST001",        "_TST001_",         "", "", DiagnosticSeverity.Warning, true),
                 new DiagnosticDescriptor("TST001",        "_TST001.002_",     "", "", DiagnosticSeverity.Warning, true),
                 new DiagnosticDescriptor("TST001",        "_TST001.003_",     "", "", DiagnosticSeverity.Warning, true),
+
+                // Descriptors with same values should not get distinct entries in log
+                new DiagnosticDescriptor("TST002", "", "", "", DiagnosticSeverity.Warning, true),
+                new DiagnosticDescriptor("TST002", "", "", "", DiagnosticSeverity.Warning, true),
+
+                // Changing only the message format (which we do not write out) should not produce a distinct entry in log.
+                new DiagnosticDescriptor("TST002", "", "messageFormat", "", DiagnosticSeverity.Warning, true),
+
+                // Changing any property that we do write out should create a distinct entry
+                new DiagnosticDescriptor("TST002", "title_001", "", "", DiagnosticSeverity.Warning, true),
+                new DiagnosticDescriptor("TST002", "", "", "category_002", DiagnosticSeverity.Warning, true),
+                new DiagnosticDescriptor("TST002", "", "", "", DiagnosticSeverity.Error /*003*/, true),
+                new DiagnosticDescriptor("TST002", "", "", "", DiagnosticSeverity.Warning, isEnabledByDefault: false /*004*/),
+                new DiagnosticDescriptor("TST002", "", "", "", DiagnosticSeverity.Warning, true, "description_005"),
             };
 
             var stream = new MemoryStream();
@@ -154,6 +169,65 @@ public void DescriptorIdCollision()
             ""warningLevel"": 1
           }
         },
+        {
+          ""ruleId"": ""TST002"",
+          ""level"": ""warning"",
+          ""properties"": {
+            ""warningLevel"": 1
+          }
+        },
+        {
+          ""ruleId"": ""TST002"",
+          ""level"": ""warning"",
+          ""properties"": {
+            ""warningLevel"": 1
+          }
+        },
+        {
+          ""ruleId"": ""TST002"",
+          ""level"": ""warning"",
+          ""message"": ""messageFormat"",
+          ""properties"": {
+            ""warningLevel"": 1
+          }
+        },
+        {
+          ""ruleId"": ""TST002"",
+          ""ruleKey"": ""TST002.001"",
+          ""level"": ""warning"",
+          ""properties"": {
+            ""warningLevel"": 1
+          }
+        },
+        {
+          ""ruleId"": ""TST002"",
+          ""ruleKey"": ""TST002.002"",
+          ""level"": ""warning"",
+          ""properties"": {
+            ""warningLevel"": 1
+          }
+        },
+        {
+          ""ruleId"": ""TST002"",
+          ""ruleKey"": ""TST002.003"",
+          ""level"": ""error""
+        },
+        {
+          ""ruleId"": ""TST002"",
+          ""ruleKey"": ""TST002.004"",
+          ""level"": ""warning"",
+          ""properties"": {
+            ""warningLevel"": 1
+          }
+        },
+        {
+          ""ruleId"": ""TST002"",
+          ""ruleKey"": ""TST002.005"",
+          ""level"": ""warning"",
+          ""properties"": {
+            ""warningLevel"": 1
+          }
+        },
         {
           ""ruleId"": ""TST001.001"",
           ""level"": ""warning"",
@@ -183,6 +257,65 @@ public void DescriptorIdCollision()
           ""properties"": {
             ""warningLevel"": 1
           }
+        },
+        {
+          ""ruleId"": ""TST002"",
+          ""level"": ""warning"",
+          ""properties"": {
+            ""warningLevel"": 1
+          }
+        },
+        {
+          ""ruleId"": ""TST002"",
+          ""level"": ""warning"",
+          ""properties"": {
+            ""warningLevel"": 1
+          }
+        },
+        {
+          ""ruleId"": ""TST002"",
+          ""level"": ""warning"",
+          ""message"": ""messageFormat"",
+          ""properties"": {
+            ""warningLevel"": 1
+          }
+        },
+        {
+          ""ruleId"": ""TST002"",
+          ""ruleKey"": ""TST002.001"",
+          ""level"": ""warning"",
+          ""properties"": {
+            ""warningLevel"": 1
+          }
+        },
+        {
+          ""ruleId"": ""TST002"",
+          ""ruleKey"": ""TST002.002"",
+          ""level"": ""warning"",
+          ""properties"": {
+            ""warningLevel"": 1
+          }
+        },
+        {
+          ""ruleId"": ""TST002"",
+          ""ruleKey"": ""TST002.003"",
+          ""level"": ""error""
+        },
+        {
+          ""ruleId"": ""TST002"",
+          ""ruleKey"": ""TST002.004"",
+          ""level"": ""warning"",
+          ""properties"": {
+            ""warningLevel"": 1
+          }
+        },
+        {
+          ""ruleId"": ""TST002"",
+          ""ruleKey"": ""TST002.005"",
+          ""level"": ""warning"",
+          ""properties"": {
+            ""warningLevel"": 1
+          }
         }
       ],
       ""rules"": {
@@ -217,6 +350,51 @@ public void DescriptorIdCollision()
           ""properties"": {
             ""isEnabledByDefault"": true
           }
+        },
+        ""TST002"": {
+          ""id"": ""TST002"",
+          ""defaultLevel"": ""warning"",
+          ""properties"": {
+            ""isEnabledByDefault"": true
+          }
+        },
+        ""TST002.001"": {
+          ""id"": ""TST002"",
+          ""shortDescription"": ""title_001"",
+          ""defaultLevel"": ""warning"",
+          ""properties"": {
+            ""isEnabledByDefault"": true
+          }
+        },
+        ""TST002.002"": {
+          ""id"": ""TST002"",
+          ""defaultLevel"": ""warning"",
+          ""properties"": {
+            ""category"": ""category_002"",
+            ""isEnabledByDefault"": true
+          }
+        },
+        ""TST002.003"": {
+          ""id"": ""TST002"",
+          ""defaultLevel"": ""error"",
+          ""properties"": {
+            ""isEnabledByDefault"": true
+          }
+        },
+        ""TST002.004"": {
+          ""id"": ""TST002"",
+          ""defaultLevel"": ""warning"",
+          ""properties"": {
+            ""isEnabledByDefault"": false
+          }
+        },
+        ""TST002.005"": {
+          ""id"": ""TST002"",
+          ""fullDescription"": ""description_005"",
+          ""defaultLevel"": ""warning"",
+          ""properties"": {
+            ""isEnabledByDefault"": true
+          }
         }
       }
     }

src/Compilers/Core/Portable/CommandLine/ErrorLogger.cs

@@ -317,7 +317,7 @@ private sealed class DiagnosticDescriptorSet
             private Dictionary<string, int> _counters = new Dictionary<string, int>();
 
             // DiagnosticDescriptor -> unique key
-            private Dictionary<DiagnosticDescriptor, string> _keys = new Dictionary<DiagnosticDescriptor, string>();
+            private Dictionary<DiagnosticDescriptor, string> _keys = new Dictionary<DiagnosticDescriptor, string>(new Comparer());
 
             /// <summary>
             /// The total number of descriptors in the set.
@@ -381,6 +381,54 @@ public string Add(DiagnosticDescriptor descriptor)
                 list.Sort((x, y) => string.CompareOrdinal(x.Key, y.Key));
                 return list;
             }
+
+            /// <summary>
+            /// Compares descriptors by the values that we write to the log and nothing else.
+            /// 
+            /// We cannot use the IEquatable implementation because it includes message format 
+            /// and we don't write it out. It also ignores tags, which we do write.
+            /// </summary>
+            private sealed class Comparer : IEqualityComparer<DiagnosticDescriptor>
+            {
+                public bool Equals(DiagnosticDescriptor x, DiagnosticDescriptor y)
+                {
+                    if (ReferenceEquals(x, y))
+                        return true;
+
+                    if (ReferenceEquals(x, null) || ReferenceEquals(y, null))
+                        return false;
+
+                   return (x.Category == y.Category
+                        && x.DefaultSeverity == y.DefaultSeverity
+                        && x.Description.Equals(y.Description)
+                        && x.HelpLinkUri == y.HelpLinkUri
+                        && x.Id == y.Id
+                        && x.IsEnabledByDefault == y.IsEnabledByDefault
+                        && x.Title.Equals(y.Title)
+                        && x.CustomTags.SequenceEqual(y.CustomTags));
+                }
+
+                public int GetHashCode(DiagnosticDescriptor obj)
+                {
+                    if (ReferenceEquals(obj, null))
+                        return 0;
+
+                    int hash = Hash.Combine(obj.Category.GetHashCode(),
+                        Hash.Combine(obj.DefaultSeverity.GetHashCode(),
+                        Hash.Combine(obj.Description.GetHashCode(),
+                        Hash.Combine(obj.HelpLinkUri.GetHashCode(),
+                        Hash.Combine(obj.Id.GetHashCode(),
+                        Hash.Combine(obj.IsEnabledByDefault.GetHashCode(),
+                        obj.Title.GetHashCode()))))));
+
+                    foreach (string tag in obj.CustomTags)
+                    {
+                        hash = Hash.Combine(tag, hash);
+                    }
+
+                    return hash;
+                }
+            }
         }
     }
 }