Improve LINQ decompiler to support combining lambda parameter names if they syntactically refer to the same range variable

ICSharpCode.Decompiler/CSharp/Transforms/CombineQueryExpressions.cs

@@ -16,12 +16,12 @@
 // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 // DEALINGS IN THE SOFTWARE.
 
-using System;
 using System.Collections.Generic;
 using System.Linq;
 
 using ICSharpCode.Decompiler.CSharp.Syntax;
 using ICSharpCode.Decompiler.CSharp.Syntax.PatternMatching;
+using ICSharpCode.Decompiler.Util;
 
 namespace ICSharpCode.Decompiler.CSharp.Transforms
 {
@@ -54,12 +54,10 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 				next = child.NextSibling;
 				CombineQueries(child, fromOrLetIdentifiers);
 			}
-			QueryExpression query = node as QueryExpression;
-			if (query != null)
+			if (node is QueryExpression query)
 			{
 				QueryFromClause fromClause = (QueryFromClause)query.Clauses.First();
-				QueryExpression innerQuery = fromClause.Expression as QueryExpression;
-				if (innerQuery != null)
+				if (fromClause.Expression is QueryExpression innerQuery)
 				{
 					if (TryRemoveTransparentIdentifier(query, fromClause, innerQuery, fromOrLetIdentifiers))
 					{
@@ -165,11 +163,8 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 			{
 				RemoveTransparentIdentifierReferences(child, fromOrLetIdentifiers);
 			}
-			MemberReferenceExpression mre = node as MemberReferenceExpression;
-			if (mre != null)
-			{
-				IdentifierExpression ident = mre.Target as IdentifierExpression;
-				if (ident != null && CSharpDecompiler.IsTransparentIdentifier(ident.Identifier))
+			if (node is MemberReferenceExpression mre && mre.Target is IdentifierExpression ident
+				&& CSharpDecompiler.IsTransparentIdentifier(ident.Identifier))
 			{
 				IdentifierExpression newIdent = new IdentifierExpression(mre.MemberName);
 				mre.TypeArguments.MoveTo(newIdent.TypeArguments);
@@ -182,7 +177,6 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 			}
 		}
 	}
-	}
 
 	public class LetIdentifierAnnotation
 	{

ICSharpCode.Decompiler/CSharp/Transforms/IntroduceQueryExpressions.cs

@@ -17,10 +17,10 @@
 // DEALINGS IN THE SOFTWARE.
 
 using System;
-using System.Diagnostics;
 using System.Linq;
 
 using ICSharpCode.Decompiler.CSharp.Syntax;
+using ICSharpCode.Decompiler.IL;
 
 namespace ICSharpCode.Decompiler.CSharp.Transforms
 {
@@ -54,13 +54,14 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 				while (IsDegenerateQuery(innerQuery))
 				{
 					QueryFromClause innerFromClause = (QueryFromClause)innerQuery.Clauses.First();
-					if (fromClause.Identifier != innerFromClause.Identifier)
-						break;
+					ILVariable innerVariable = innerFromClause.Annotation<ILVariableResolveResult>()?.Variable;
+					ILVariable rangeVariable = fromClause.Annotation<ILVariableResolveResult>()?.Variable;
 					// Replace the fromClause with all clauses from the inner query
 					fromClause.Remove();
 					QueryClause insertionPos = null;
 					foreach (var clause in innerQuery.Clauses)
 					{
+						CombineRangeVariables(clause, innerVariable, rangeVariable);
 						query.Clauses.InsertAfter(insertionPos, insertionPos = clause.Detach());
 					}
 					fromClause = innerFromClause;
@@ -69,6 +70,20 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 			}
 		}
 
+		private void CombineRangeVariables(QueryClause clause, ILVariable oldVariable, ILVariable newVariable)
+		{
+			foreach (var identifier in clause.DescendantNodes().OfType<Identifier>())
+			{
+				var variable = identifier.Parent.Annotation<ILVariableResolveResult>()?.Variable;
+				if (variable == oldVariable)
+				{
+					identifier.Parent.RemoveAnnotations<ILVariableResolveResult>();
+					identifier.Parent.AddAnnotation(new ILVariableResolveResult(newVariable));
+					identifier.ReplaceWith(Identifier.Create(newVariable.Name));
+				}
+			}
+		}
+
 		bool IsDegenerateQuery(QueryExpression query)
 		{
 			if (query == null)