Produce warning on duplicate analyzer references

Author: Youssef1313

src/Compilers/CSharp/Portable/CSharpResources.resx

@@ -6781,63 +6781,54 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
   <data name="ERR_RefFieldInNonRefStruct" xml:space="preserve">
     <value>A ref field can only be declared in a ref struct.</value>
   </data>
-
   <data name="WRN_UseDefViolationPropertySupportedVersion" xml:space="preserve">
     <value>Auto-implemented property '{0}' is read before being explicitly assigned, causing a preceding implicit assignment of 'default'.</value>
   </data>
   <data name="WRN_UseDefViolationPropertySupportedVersion_Title" xml:space="preserve">
     <value>Auto-implemented property is read before being explicitly assigned, causing a preceding implicit assignment of 'default'.</value>
   </data>
-
   <data name="WRN_UseDefViolationFieldSupportedVersion" xml:space="preserve">
     <value>Field '{0}' is read before being explicitly assigned, causing a preceding implicit assignment of 'default'.</value>
   </data>
   <data name="WRN_UseDefViolationFieldSupportedVersion_Title" xml:space="preserve">
     <value>Field is read before being explicitly assigned, causing a preceding implicit assignment of 'default'.</value>
   </data>
-
   <data name="WRN_UseDefViolationThisSupportedVersion" xml:space="preserve">
     <value>The 'this' object is read before all of its fields have been assigned, causing preceding implicit assignments of 'default' to non-explicitly assigned fields.</value>
   </data>
   <data name="WRN_UseDefViolationThisSupportedVersion_Title" xml:space="preserve">
     <value>The 'this' object is read before all of its fields have been assigned, causing preceding implicit assignments of 'default' to non-explicitly assigned fields.</value>
   </data>
-
   <data name="WRN_UnassignedThisAutoPropertySupportedVersion" xml:space="preserve">
     <value>Control is returned to caller before auto-implemented property '{0}' is explicitly assigned, causing a preceding implicit assignment of 'default'.</value>
   </data>
   <data name="WRN_UnassignedThisAutoPropertySupportedVersion_Title" xml:space="preserve">
     <value>Control is returned to caller before auto-implemented property is explicitly assigned, causing a preceding implicit assignment of 'default'.</value>
   </data>
-
   <data name="WRN_UnassignedThisSupportedVersion" xml:space="preserve">
     <value>Control is returned to caller before field '{0}' is explicitly assigned, causing a preceding implicit assignment of 'default'.</value>
   </data>
   <data name="WRN_UnassignedThisSupportedVersion_Title" xml:space="preserve">
     <value>Control is returned to caller before field is explicitly assigned, causing a preceding implicit assignment of 'default'.</value>
   </data>
-
   <data name="ERR_UseDefViolationFieldUnsupportedVersion" xml:space="preserve">
     <value>Use of possibly unassigned field '{0}'. Consider updating to language version '{1}' to auto-default the field.</value>
   </data>
   <data name="ERR_UseDefViolationPropertyUnsupportedVersion" xml:space="preserve">
     <value>Use of possibly unassigned auto-implemented property '{0}'. Consider updating to language version '{1}' to auto-default the property.</value>
   </data>
-
   <data name="WRN_UseDefViolationFieldUnsupportedVersion" xml:space="preserve">
     <value>Use of possibly unassigned field '{0}'. Consider updating to language version '{1}' to auto-default the field.</value>
   </data>
   <data name="WRN_UseDefViolationFieldUnsupportedVersion_Title" xml:space="preserve">
     <value>Use of possibly unassigned field. Consider updating the language version to auto-default the field.</value>
   </data>
-
   <data name="WRN_UseDefViolationPropertyUnsupportedVersion" xml:space="preserve">
     <value>Use of possibly unassigned auto-implemented property '{0}'. Consider updating to language version '{1}' to auto-default the property.</value>
   </data>
   <data name="WRN_UseDefViolationPropertyUnsupportedVersion_Title" xml:space="preserve">
     <value>Use of possibly unassigned auto-implemented property. Consider updating the language version to auto-default the property.</value>
   </data>
-
   <data name="ERR_UnsupportedTypeForSlicePattern" xml:space="preserve">
     <value>Slice patterns may not be used for a value of type '{0}'.</value>
   </data>
@@ -7211,4 +7202,10 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
   <data name="ERR_RuntimeDoesNotSupportRefFields" xml:space="preserve">
     <value>Target runtime doesn't support ref fields.</value>
   </data>
-</root>
+  <data name="WRN_DuplicateAnalyzerReference" xml:space="preserve">
+    <value>Analyzer reference '{0}' specified multiple times</value>
+  </data>
+  <data name="WRN_DuplicateAnalyzerReference_Title" xml:space="preserve">
+    <value>Analyzer reference specified multiple times</value>
+  </data>
+</root>

src/Compilers/CSharp/Portable/Errors/ErrorCode.cs

@@ -2113,6 +2113,7 @@ internal enum ErrorCode
         ERR_ScopedTypeNameDisallowed = 9062,
         ERR_UnscopedRefAttributeUnsupportedTarget = 9063,
         ERR_RuntimeDoesNotSupportRefFields = 9064,
+        WRN_DuplicateAnalyzerReference = 9065,
 
         #endregion
 

src/Compilers/CSharp/Portable/Errors/ErrorFacts.cs

@@ -501,6 +501,7 @@ internal static int GetWarningLevel(ErrorCode code)
                 case ErrorCode.WRN_UnassignedThisSupportedVersion:
                 case ErrorCode.WRN_ObsoleteMembersShouldNotBeRequired:
                 case ErrorCode.WRN_AnalyzerReferencesNewerCompiler:
+                case ErrorCode.WRN_DuplicateAnalyzerReference:
                     return 1;
                 default:
                     return 0;
@@ -2214,6 +2215,7 @@ internal static bool IsBuildOnlyDiagnostic(ErrorCode code)
                 case ErrorCode.ERR_ScopedTypeNameDisallowed:
                 case ErrorCode.ERR_UnscopedRefAttributeUnsupportedTarget:
                 case ErrorCode.ERR_RuntimeDoesNotSupportRefFields:
+                case ErrorCode.WRN_DuplicateAnalyzerReference:
                     return false;
                 default:
                     // NOTE: All error codes must be explicitly handled in this switch statement

src/Compilers/CSharp/Portable/Errors/MessageProvider.cs

@@ -179,6 +179,7 @@ internal override bool ShouldAssertExpectedMessageArgumentsLength(int errorCode)
         public override int WRN_UnableToLoadAnalyzer => (int)ErrorCode.WRN_UnableToLoadAnalyzer;
         public override int WRN_AnalyzerReferencesFramework => (int)ErrorCode.WRN_AnalyzerReferencesFramework;
         public override int WRN_AnalyzerReferencesNewerCompiler => (int)ErrorCode.WRN_AnalyzerReferencesNewerCompiler;
+        public override int WRN_DuplicateAnalyzerReference => (int)ErrorCode.WRN_DuplicateAnalyzerReference;
         public override int INF_UnableToLoadSomeTypesInAnalyzer => (int)ErrorCode.INF_UnableToLoadSomeTypesInAnalyzer;
         public override int ERR_CantReadRulesetFile => (int)ErrorCode.ERR_CantReadRulesetFile;
         public override int ERR_CompileCancelled => (int)ErrorCode.ERR_CompileCancelled;