Properly handle expression variable declared within VariableDeclarato…

…rSyntax.ArgumentList in ‘fixed’, ‘for’ and ‘using’ statements.

Related to dotnet#12597.
Fixes dotnet#13459, dotnet#13460.

src/Compilers/CSharp/Portable/Binder/Binder_Statements.cs

@@ -954,7 +954,7 @@ protected BoundLocalDeclaration BindVariableDeclaration(
  return new BoundLocalDeclaration(associatedSyntaxNode, localSymbol, boundDeclType, initializerOpt, arguments, hasErrors);
  }
 
- private ImmutableArray<BoundExpression> BindDeclaratorArguments(VariableDeclaratorSyntax declarator, DiagnosticBag diagnostics)
+ internal ImmutableArray<BoundExpression> BindDeclaratorArguments(VariableDeclaratorSyntax declarator, DiagnosticBag diagnostics)
  {
  // It is possible that we have a bracketed argument list, like "int x[];" or "int x[123];" 
  // in a non-fixed-size-array declaration . This is a common error made by C++ programmers. 

src/Compilers/CSharp/Portable/Binder/FixedStatementBinder.cs

@@ -30,10 +30,8 @@ override protected ImmutableArray<LocalSymbol> BuildLocals()
  {
  locals.Add(MakeLocal(_syntax.Declaration, declarator, LocalDeclarationKind.FixedVariable));
 
- if (declarator.Initializer != null)
- {
- ExpressionVariableFinder.FindExpressionVariables(this, locals, declarator.Initializer.Value);
- }
+ // also gather expression-declared variables from the bracketed argument lists and the initializers
+ ExpressionVariableFinder.FindExpressionVariables(this, locals, declarator);
  }
 
  return locals.ToImmutable();

src/Compilers/CSharp/Portable/Binder/ForLoopBinder.cs

@@ -40,7 +40,9 @@ override protected ImmutableArray<LocalSymbol> BuildLocals()
  {
  var localSymbol = MakeLocal(_syntax.Declaration, vdecl, LocalDeclarationKind.ForInitializerVariable);
  locals.Add(localSymbol);
- ExpressionVariableFinder.FindExpressionVariables(this, locals, vdecl.Initializer?.Value);
+
+ // also gather expression-declared variables from the bracketed argument lists and the initializers
+ ExpressionVariableFinder.FindExpressionVariables(this, locals, vdecl);
  }
  }
  else

src/Compilers/CSharp/Portable/Binder/LocalBinderFactory.cs

@@ -360,10 +360,7 @@ public override void VisitUsingStatement(UsingStatementSyntax node)
  {
  foreach (VariableDeclaratorSyntax declarator in declarationSyntax.Variables)
  {
- if (declarator.Initializer != null)
- {
- Visit(declarator.Initializer.Value, usingBinder);
- }
+ Visit(declarator, usingBinder);
  }
  }
 
@@ -401,10 +398,7 @@ public override void VisitForStatement(ForStatementSyntax node)
  {
  foreach (var variable in declaration.Variables)
  {
- if (variable.Initializer != null)
- {
- Visit(variable.Initializer.Value, binder);
- }
+ Visit(variable, binder);
  }
  }
  else
@@ -478,10 +472,7 @@ public override void VisitFixedStatement(FixedStatementSyntax node)
  {
  foreach (VariableDeclaratorSyntax declarator in node.Declaration.Variables)
  {
- if (declarator.Initializer != null)
- {
- Visit(declarator.Initializer.Value, binder);
- }
+ Visit(declarator, binder);
  }
  }
 
@@ -651,14 +642,16 @@ public override void VisitLocalDeclarationStatement(LocalDeclarationStatementSyn
  {
  foreach (var decl in node.Declaration.Variables)
  {
- var value = decl.Initializer?.Value;
- if (value != null)
- {
- Visit(value, _enclosing);
- }
+ Visit(decl);
  }
  }
 
+ public override void VisitVariableDeclarator(VariableDeclaratorSyntax node)
+ {
+ Visit(node.ArgumentList);
+ Visit(node.Initializer?.Value);
+ }
+
  public override void VisitDeconstructionDeclarationStatement(DeconstructionDeclarationStatementSyntax node)
  {
  Visit(node.Assignment.Value, _enclosing);

src/Compilers/CSharp/Portable/Binder/UsingStatementBinder.cs

@@ -40,10 +40,8 @@ override protected ImmutableArray<LocalSymbol> BuildLocals()
  {
  locals.Add(MakeLocal(declarationSyntax, declarator, LocalDeclarationKind.UsingVariable));
 
- if (declarator.Initializer != null)
- {
- ExpressionVariableFinder.FindExpressionVariables(this, locals, declarator.Initializer.Value);
- }
+ // also gather expression-declared variables from the bracketed argument lists and the initializers
+ ExpressionVariableFinder.FindExpressionVariables(this, locals, declarator);
  }
 
  return locals.ToImmutableAndFree();

src/Compilers/CSharp/Portable/FlowAnalysis/DataFlowPass.cs

@@ -1660,7 +1660,7 @@ public override BoundNode VisitUsingStatement(BoundUsingStatement node)
  }
  }
 
- Debug.Assert(localsOpt.Where(l => l.DeclarationKind != LocalDeclarationKind.PatternVariable).All(_usedVariables.Contains));
+ Debug.Assert(localsOpt.Where(l => l.DeclarationKind == LocalDeclarationKind.UsingVariable).All(_usedVariables.Contains));
 
  return result;
  }

src/Compilers/CSharp/Portable/Symbols/Source/SourceLocalSymbol.cs

@@ -752,23 +752,7 @@ protected override TypeSymbol InferTypeOfVarVariable(DiagnosticBag diagnostics)
  // This occurs, for example, in
  // int x, y[out var Z, 1 is int I];
  // for (int x, y[out var Z, 1 is int I]; ;) {}
- var declarator = (VariableDeclaratorSyntax)_nodeToBind;
- if (declarator.ArgumentList != null)
- {
- foreach (var arg in declarator.ArgumentList.Arguments)
- {
- var expression = arg.Expression;
- if (expression.Kind() == SyntaxKind.DeclarationExpression)
- {
- this.SetType(_nodeBinder.CreateErrorType("var"));
- // no error is necessary, as they would be dropped on the floor by the caller
- }
- else
- {
- _nodeBinder.BindExpression(expression, diagnostics);
- }
- }
- }
+ _nodeBinder.BindDeclaratorArguments((VariableDeclaratorSyntax)_nodeToBind, diagnostics);
  break;
  default:
  _nodeBinder.BindExpression((ExpressionSyntax)_nodeToBind, diagnostics);