lastStep undefined issue

[tjk]

Description

Still need to understand why this is happening... but there seems to at least be a problem in the code.

Comment + check for nullish lastStep here:

ai/packages/ai/core/generate-text/stream-text.ts

Lines 534 to 536 in 952cbdf

	// from last step (when there are errors there may be no last step)
	const lastStep = recordedSteps[recordedSteps.length - 1];
	if (lastStep) {

but then accessed without care here:

ai/packages/ai/core/generate-text/stream-text.ts

Line 569 in 952cbdf

toolCalls: lastStep.toolCalls,

Produces this stack trace:

Cause: TypeError: Cannot read properties of undefined (reading 'toolCalls')
    at Object.flush (turbopack://[project]/node_modules/.pnpm/[email protected][email protected][email protected]/node_modules/ai/core/generate-text/stream-text.ts:571:21)
  569 |             toolCalls: lastStep.toolCalls,
  570 |             toolResults: lastStep.toolResults,
> 571 |             request: lastStep.request ?? {},
      |                     ^
  572 |             response: lastStep.response,
  573 |             warnings: lastStep.warnings,

AI provider

Anthropic. Don't get this error With OpenAI, I think. Probably something to do with tools declaration, but would be nice to get better feedback than just that stack above.

[tjk]

It looks like this issue might be related (and what I'm running into): #3422

[lgrammel]

Can you share the code you use to call streamText?

Anthropic does not support structured outputs with streamText (we use tool calls with streamObject/generateObject), so this might not work with Anthropic.

[Taofeeq-deru]

I'm getting this same error, using steamText not steamObject, with openai

[lgrammel]

Can you check if you still encounter this issue if you downgrade ai to 4.0.14?

[Taofeeq-deru]

hi, forgot to reply this

I didn't have to downgrade it, was previously sending only text and tool-result content types in my context window, changed that and included tool-call too, and all worked fine after