FlatExpression: track lambda, block-with-vars, goto/label, and try-catch node indices during construction

[Copilot]

TryCollectInfo traverses the entire expression tree to discover nested lambdas, block-scoped variables, goto/label pairs, and try regions. For FlatExpression (FE), all of this work can be done during construction — the same way ClosureConstants is already pre-collected — eliminating the O(tree_size) scan.

Changes

• ExprTree.LambdaNodes — tracks indices of every lambda node; the root is RootIndex, all others are nested lambdas
• ExprTree.BlocksWithVariables — tracks indices of block nodes that carry explicit variable declarations (children.Count == 2), covering TryCollectInfo's PushBlockWithVars/PopBlock tracking
• ExprTree.GotoNodes — tracks indices of ExpressionType.Goto nodes (goto/return/break/continue family), covering the goto-count side of TargetToGotosAndLabels
• ExprTree.LabelNodes — tracks indices of ExpressionType.Label expression nodes, covering the label-count side of TargetToGotosAndLabels
• ExprTree.TryCatchNodes — tracks indices of ExpressionType.Try nodes (try/catch, try/finally, try/fault), covering the HasComplexExpression = true marking

All five lists are populated in both the direct factory-API path and Builder.AddExpression (the FromExpression path), so the same metadata is available regardless of how the ExprTree was built.

Usage

var fe = default(ExprTree);
var x = fe.ParameterOf<int>("x");
var inner = fe.Lambda<Func<int>>(x);
fe.RootIndex = fe.Lambda<Func<int, Func<int>>>(inner, x);

// fe.LambdaNodes.Count == 2  (root + nested)
// nested lambdas = all LambdaNodes entries where index != fe.RootIndex

// fe.BlocksWithVariables — blocks that need PushBlockWithVars treatment
// fe.GotoNodes / fe.LabelNodes — for goto↔label linking without traversal
// fe.TryCatchNodes — try regions that force HasComplexExpression = true

Callers can now enumerate all of these node categories in O(node_count) without a full tree walk. This is the groundwork for eliminating the separate TryCollectInfo phase for FE-built expressions; subsequent work can leverage these lists to pre-compute non-passed parameters, block-local variables, and label linkage at construction time.

[dadhi]

@copilot what about other things, blocks, try catch, goto/labels

[Copilot]

@copilot what about other things, blocks, try catch, goto/labels

Done in commit 60a4f93. Added three more pre-collected index lists to ExprTree, mirroring the LambdaNodes pattern:

• BlocksWithVariables — block node indices that carry explicit variable declarations (children.Count == 2), covering TryCollectInfo's PushBlockWithVars/PopBlock tracking
• GotoNodes — ExpressionType.Goto node indices (goto/return/break/continue family), covering the TargetToGotosAndLabels goto-count side
• LabelNodes — ExpressionType.Label expression node indices, covering the label-count side
• TryCatchNodes — ExpressionType.Try node indices (try/catch, try/finally, try/fault), covering the HasComplexExpression = true marking

All four are populated in both the direct factory-API path and Builder.AddExpression (FromExpression), with 6 new tests added.

[dadhi]

Right now we are just creating indexes so we can collecting the indexes for imporant node types.