Implicit field initialization in struct constructors

src/Compilers/CSharp/Portable/CSharpResources.resx

@@ -6691,6 +6691,9 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
   <data name="IDS_FeatureLineSpanDirective" xml:space="preserve">
     <value>line span directive</value>
   </data>
+  <data name="IDS_FeatureImplicitInitializationInStructConstructors" xml:space="preserve">
+    <value>implicit initialization in struct constructors</value>
+  </data>
   <data name="ERR_LineSpanDirectiveInvalidValue" xml:space="preserve">
     <value>The #line directive value is missing or out of range</value>
   </data>

src/Compilers/CSharp/Portable/Compiler/MethodCompiler.cs

@@ -1015,7 +1015,7 @@ private void CompileMethod(
                     }
 
                     var unusedDiagnostics = DiagnosticBag.GetInstance();
-                    DefiniteAssignmentPass.Analyze(_compilation, methodSymbol, initializerStatements, unusedDiagnostics, requireOutParamsAssigned: false);
+                    DefiniteAssignmentPass.Analyze(_compilation, methodSymbol, initializerStatements, unusedDiagnostics, out _, requireOutParamsAssigned: false);
                     DiagnosticsPass.IssueDiagnostics(_compilation, initializerStatements, BindingDiagnosticBag.Discarded, methodSymbol);
                     unusedDiagnostics.Free();
                 }
@@ -1077,7 +1077,7 @@ processedInitializers.AfterInitializersState is null &&
                                 // Flow analysis over the initializers is necessary in order to find assignments to fields.
                                 // Bodies of implicit constructors do not get flow analysis later, so the initializers
                                 // are analyzed here.
-                                DefiniteAssignmentPass.Analyze(_compilation, methodSymbol, analyzedInitializers, diagsForCurrentMethod.DiagnosticBag, requireOutParamsAssigned: false);
+                                DefiniteAssignmentPass.Analyze(_compilation, methodSymbol, analyzedInitializers, diagsForCurrentMethod.DiagnosticBag, out _, requireOutParamsAssigned: false);
                             }
 
                             // In order to get correct diagnostics, we need to analyze initializers and the body together.
@@ -1089,7 +1089,7 @@ processedInitializers.AfterInitializersState is null &&
                         {
                             // These analyses check for diagnostics in lambdas.
                             // Control flow analysis and implicit return insertion are unnecessary.
-                            DefiniteAssignmentPass.Analyze(_compilation, methodSymbol, analyzedInitializers, diagsForCurrentMethod.DiagnosticBag, requireOutParamsAssigned: false);
+                            DefiniteAssignmentPass.Analyze(_compilation, methodSymbol, analyzedInitializers, diagsForCurrentMethod.DiagnosticBag, out _, requireOutParamsAssigned: false);
                             DiagnosticsPass.IssueDiagnostics(_compilation, analyzedInitializers, diagsForCurrentMethod, methodSymbol);
                         }
                     }
@@ -1122,7 +1122,7 @@ processedInitializers.AfterInitializersState is null &&
                 BoundBlock flowAnalyzedBody = null;
                 if (body != null)
                 {
-                    flowAnalyzedBody = FlowAnalysisPass.Rewrite(methodSymbol, body, diagsForCurrentMethod.DiagnosticBag, hasTrailingExpression: hasTrailingExpression, originalBodyNested: originalBodyNested);
+                    flowAnalyzedBody = FlowAnalysisPass.Rewrite(methodSymbol, body, compilationState, diagsForCurrentMethod, hasTrailingExpression: hasTrailingExpression, originalBodyNested: originalBodyNested);
                 }
 
                 bool hasErrors = _hasDeclarationErrors || diagsForCurrentMethod.HasAnyErrors() || processedInitializers.HasErrors;

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

@@ -42,6 +42,23 @@ internal static CSDiagnosticInfo Add(this DiagnosticBag diagnostics, ErrorCode c
             return info;
         }
 
+        /// <summary>
+        /// Add a diagnostic to the bag.
+        /// </summary>
+        /// <param name="diagnostics"></param>
+        /// <param name="code"></param>
+        /// <param name="location"></param>
+        /// <param name="isSuppressed"></param>
+        /// <param name="args"></param>
+        /// <returns></returns>
+        internal static CSDiagnosticInfo Add(this DiagnosticBag diagnostics, ErrorCode code, Location location, bool isSuppressed, params object[] args)
+        {
+            var info = new CSDiagnosticInfo(code, args);
+            var diag = new CSDiagnostic(info, location, isSuppressed);
+            diagnostics.Add(diag);
+            return info;
+        }
+
         internal static CSDiagnosticInfo Add(this DiagnosticBag diagnostics, ErrorCode code, Location location, ImmutableArray<Symbol> symbols, params object[] args)
         {
             var info = new CSDiagnosticInfo(code, args, symbols, ImmutableArray<Location>.Empty);

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

@@ -244,6 +244,7 @@ internal enum MessageID
 
         IDS_FeatureCacheStaticMethodGroupConversion = MessageBase + 12816,
         IDS_FeatureRawStringLiterals = MessageBase + 12817,
+        IDS_FeatureImplicitInitializationInStructConstructors = MessageBase + 12818,
     }
 
     // Message IDs may refer to strings that need to be localized.
@@ -360,6 +361,7 @@ internal static LanguageVersion RequiredVersion(this MessageID feature)
                 case MessageID.IDS_FeatureListPattern: // semantic check
                 case MessageID.IDS_FeatureCacheStaticMethodGroupConversion: // lowering check
                 case MessageID.IDS_ParameterNullChecking: // syntax check
+                case MessageID.IDS_FeatureImplicitInitializationInStructConstructors: // semantic check
                     return LanguageVersion.Preview;
 
                 // C# 10.0 features.