What causes "[BUG] tried to replace 'ASTType' on 'ValueContainer'" in vitessio/vitess?

Inspect the rewrite pass stack trace to find which walker change proposes replacing the ASTType child

[BUG] tried to replace 'ASTType' on 'ValueContainer'

Error message

[BUG] tried to replace 'ASTType' on 'ValueContainer'

What it means

This panic lives inside the generated AST rewriter for the ValueContainer node. The 'ASTType' child of a ValueContainer is structural and must never be rewritten, so the rewrite callback is written to panic '[BUG] tried to replace ASTType on ValueContainer' if the walker ever proposes replacing it. Hitting it means an invariant of the AST rewriting contract is violated — it is always a bug in the rewriter/walker, not in user code.

Source

Thrown at go/tools/asthelpergen/integration/ast_rewrite.go:450

func (a *application) rewriteValueContainer(parent AST, node ValueContainer, replacer replacerFunc) bool {
	if a.pre != nil {
		a.cur.replacer = replacer
		a.cur.parent = parent
		a.cur.node = node
		kontinue := !a.pre(&a.cur)
		if a.cur.revisit {
			a.cur.revisit = false
			return a.rewriteAST(parent, a.cur.node, replacer)
		}
		if kontinue {
			return true
		}
	}
	if a.collectPaths {
		a.cur.current.AddStep(uint16(ValueContainerASTType))
	}
	if !a.rewriteAST(node, node.ASTType, func(newNode, parent AST) {
		panic("[BUG] tried to replace 'ASTType' on 'ValueContainer'")
	}) {
		return false
	}
	if a.collectPaths {
		a.cur.current.Pop()
		a.cur.current.AddStep(uint16(ValueContainerASTImplementationType))
	}
	if !a.rewriteRefOfLeaf(node, node.ASTImplementationType, func(newNode, parent AST) {
		panic("[BUG] tried to replace 'ASTImplementationType' on 'ValueContainer'")
	}) {
		return false
	}
	if a.collectPaths {
		a.cur.current.Pop()
	}
	if a.post != nil {
		a.cur.replacer = replacer
		a.cur.parent = parent

View on GitHub (pinned to 01a25a7d17)

Solutions

Inspect the rewrite pass stack trace to find which walker change proposes replacing the ASTType child
Fix the rewrite callback/walker so ASTType children are skipped (not visited as replaceable) and re-run make codegen
Report upstream if it reproduces on unmodified vitess main — it indicates a codegen bug in asthelpergen rewrite generation

Defensive patterns

Strategy: try-catch

Validate before calling

// Reproduce under test with path collection enabled before merging walker changes
node.Rewrite(func(newNode, parent AST) { ... }) // run in a test with collectPaths = true

Try / catch

func() {
    defer func() {
        if r := recover(); r != nil && strings.Contains(fmt.Sprint(r), "tried to replace 'ASTType'") {
            log.Fatalf("codegen bug: rewriter touched ASTType child: %v", r)
        }
    }()
    runRewritePass(node)
}()

Prevention

Never modify ASTType children in rewrite callbacks — only value/implementation children
Re-run make codegen and sqlparser tests after any AST definition change
Treat this panic as a bug report: capture the stack trace and fix the walker, don't work around it in caller code

When it happens

Trigger: Running a rewrite pass (rewriteAST) over a ValueContainer node where the replacement logic tries to substitute the node's ASTType child instead of its value or implementation-type children; typically caused by changes to the generated walker or rewrite rules.

Common situations: After regenerating sqlparser code (make codegen) following an AST definition change, rewrite passes on type-valued containers start crashing in tests.

Related errors

AI-assisted analysis of vitessio/vitess@01a25a7d17 (2026-09-01). Data as JSON: /api/errors/d84deac2ac36389a. Report an issue: GitHub.