Extract shared walkStatements helper for microflow AST walkers

[hjotha]

Source

Follow-up from ako's review on PR #337 (merged as part of open PR).

Problem

Several microflow builder passes open-code the same recursive AST walk over MicroflowStatement bodies, each with a nearly identical switch on statement types. Concrete examples:

• `planMicroflowCallOutputDeclarations` (inner `walk`) in `cmd_microflows_builder.go`
• `countMicroflowCallOutputs` in the same file
• `collectListInputVariables` / `collectObjectInputVariables` in `cmd_microflows_builder_graph.go`
• `statementVarRefs` / `statementsVarRefs` in `cmd_microflows_builder_varutil.go`
• `bodyReturns` in `validate_microflow.go`

Each copy is ~40 lines of switch boilerplate with an `ErrorHandling` recurse arm. When a new statement type gains an `ErrorHandling` field or nested body, it must be added in every place — this is how the bugs in PR #337 (issue #405) and PR #362 surfaced.

Expected behavior

A single shared helper:

```go
func walkStatements(body []ast.MicroflowStatement, fn func(ast.MicroflowStatement))
```

does the recursion (including `IfStmt`/`LoopStmt`/`WhileStmt` bodies and every `ErrorHandling.Body`). Each caller supplies the per-node callback only. Adding a new statement type with its own body requires exactly one edit in one place.

Proposed fix

1. Introduce `walkStatements(body, fn)` in `cmd_microflows_builder_varutil.go` (or a new `cmd_microflows_builder_walk.go`).
2. Rewrite the existing walkers to call it with their per-node logic.
3. Keep `statementVarRefs` as is — that's the per-node logic, not the walker.

Related

• Reviewed in fix: reject duplicate microflow output variables #337 by ako.
• Directly related to gaps that produced Reverse retrieve incorrectly classified when output feeds add/remove-from-list statements #405, PR feat: allow expressions in add-to-list statements #362 follow-up, and the missing CreateListStmt / SendRestRequestStmt coverage.
• Part of Microflow roundtrip stabilization for large-project audit findings #332 (microflow roundtrip stabilization tracker).

[github-actions]

Issue Triage

Summary:
The issue proposes extracting a shared walkStatements helper to eliminate duplicated AST‑walking code in mxcli’s microflow builder passes.

Checklist for feature request

Required info	Present?	Details
Use case – why the feature is needed / problem it solves	✅	Describes duplicated walkers causing bugs when new statement types are added.
Proposed syntax or behavior (if applicable)	✅	Suggests func walkStatements(body []ast.MicroflowStatement, fn func(ast.MicroflowStatement)) and shows how callers would use it.
Mendix version relevance (if version‑specific)	❌	No mention of which Mendix versions the change affects or is tested against.

What’s missing:
Could you let us know which Mendix version(s) this change is relevant to (e.g., does it apply to all versions, or only certain 9.x/10.x releases)? This helps reviewers assess impact and testing needs.

Thank you for the clear proposal! Once we have the version info, we can move forward.

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