Disallow expression variables in query clauses. (#16081)

Fixes #15910
Also fixes a sequence point issue with the let expression. Specifically, the source range for the query lambda included more than the expression of the let, but included the entire query clause. It now includes only the expression, like other query clauses.

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

@@ -582,7 +582,7 @@ private void ReduceLet(LetClauseSyntax let, QueryTranslationState state, Diagnos
 
  // The bound block represents a closure scope for transparent identifiers captured in the let clause.
  // Such closures shall be associated with the lambda body expression.
- return lambdaBodyBinder.CreateBlockFromExpression(let.Expression, lambdaBodyBinder.GetDeclaredLocalsForScope(let.Expression), RefKind.None, construction, null, d);
+ return lambdaBodyBinder.CreateLambdaBlockForQueryClause(let.Expression, construction, d);
  };
 
  var lambda = MakeQueryUnboundLambda(state.RangeVariableMap(), ImmutableArray.Create(x), let.Expression, bodyFactory);
@@ -594,6 +594,17 @@ private void ReduceLet(LetClauseSyntax let, QueryTranslationState state, Diagnos
  state.fromExpression = MakeQueryClause(let, invocation, y, invocation);
  }
 
+ private BoundBlock CreateLambdaBlockForQueryClause(ExpressionSyntax expression, BoundExpression result, DiagnosticBag diagnostics)
+ {
+ var locals = this.GetDeclaredLocalsForScope(expression);
+ if (locals.Any())
+ {
+ diagnostics.Add(ErrorCode.ERR_ExpressionVariableInQueryClause, locals[0].Locations[0]);
+ }
+
+ return this.CreateBlockFromExpression(expression, locals, RefKind.None, result, expression, diagnostics);
+ }
+
  private BoundQueryClause MakeQueryClause(
  CSharpSyntaxNode syntax,
  BoundExpression expression,
@@ -648,7 +659,10 @@ private UnboundLambda MakeQueryUnboundLambda(RangeVariableMap qvm, ImmutableArra
  {
  return MakeQueryUnboundLambda(expression, new QueryUnboundLambdaState(this, qvm, parameters, (LambdaSymbol lambdaSymbol, Binder lambdaBodyBinder, DiagnosticBag diagnostics) =>
  {
- return lambdaBodyBinder.BindLambdaExpressionAsBlock(expression, diagnostics);
+ lambdaBodyBinder = lambdaBodyBinder.GetBinder(expression);
+ Debug.Assert(lambdaSymbol != null);
+ BoundExpression boundExpression = lambdaBodyBinder.BindValue(expression, diagnostics, BindValueKind.RValue);
+ return lambdaBodyBinder.CreateLambdaBlockForQueryClause(expression, boundExpression, diagnostics);
  }));
  }
 
@@ -658,13 +672,12 @@ private UnboundLambda MakeQueryUnboundLambdaWithCast(RangeVariableMap qvm, Range
  {
  lambdaBodyBinder = lambdaBodyBinder.GetBinder(expression);
  Debug.Assert(lambdaBodyBinder != null);
-
  BoundExpression boundExpression = lambdaBodyBinder.BindValue(expression, diagnostics, BindValueKind.RValue);
 
  // We transform the expression from "expr" to "expr.Cast<castTypeOpt>()".
  boundExpression = lambdaBodyBinder.MakeQueryInvocation(expression, boundExpression, "Cast", castTypeSyntax, castType, diagnostics);
 
- return lambdaBodyBinder.CreateBlockFromExpression(expression, lambdaBodyBinder.GetDeclaredLocalsForScope(expression), RefKind.None, boundExpression, expression, diagnostics);
+ return lambdaBodyBinder.CreateLambdaBlockForQueryClause(expression, boundExpression, diagnostics);
  }));
  }
 

src/Compilers/CSharp/Portable/CSharpResources.resx

@@ -4969,6 +4969,9 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
  <data name="ERR_ExpressionVariableInConstructorOrFieldInitializer" xml:space="preserve">
  <value>Out variable and pattern variable declarations are not allowed within constructor initializers, field initializers, or property initializers.</value>
  </data>
+ <data name="ERR_ExpressionVariableInQueryClause" xml:space="preserve">
+ <value>Out variable and pattern variable declarations are not allowed within a query clause.</value>
+ </data>
  <data name="ERR_SemiOrLBraceOrArrowExpected" xml:space="preserve">
  <value>{ or ; or =&gt; expected</value>
  </data>

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

@@ -1443,8 +1443,12 @@ internal enum ErrorCode
  ERR_ImplicitlyTypedOutVariableUsedInTheSameArgumentList = 8196,
  ERR_TypeInferenceFailedForImplicitlyTypedOutVariable = 8197,
  ERR_ExpressionTreeContainsOutVariable = 8198,
+ #endregion diagnostics for out var
+
+ #region more stragglers for C# 7
  ERR_VarInvocationLvalueReserved = 8199,
  ERR_ExpressionVariableInConstructorOrFieldInitializer = 8200,
- #endregion diagnostics for out var
+ ERR_ExpressionVariableInQueryClause = 8201,
+ #endregion more stragglers for C# 7
  }
 }

src/Compilers/CSharp/Test/Emit/PDB/PDBLambdaTests.cs

@@ -655,7 +655,7 @@ where b > 10
  <forward declaringType=""C"" methodName=""M"" />
  </customDebugInfo>
  <sequencePoints>
- <entry offset=""0x0"" startLine=""10"" startColumn=""17"" endLine=""10"" endColumn=""30"" />
+ <entry offset=""0x0"" startLine=""10"" startColumn=""25"" endLine=""10"" endColumn=""30"" />
  </sequencePoints>
  </method>
  <method containingType=""C+&lt;&gt;c"" name=""&lt;M&gt;b__0_1"" parameterNames=""&lt;&gt;h__TransparentIdentifier0"">