[BUG] Gemini not outputting [0]

[sergedc]

Problem (one or two sentences)

If gemini creates code with [0], the [0] disappear when the code ends up in the file.

Context (who is affected and when)

How to replicate:
System: Windows, VS code, Roo code extension (any version for the past 2 weeks),
API provider: Google Gemini
Model: gemini-2.5-pro

Reproduction steps

Prompt:
Create a python file that creates a list of 10 fruits (you choose them) then put the first one in the variable "myfruit"

Result:
fruits = ["Apple", "Banana", "Orange", "Grape", "Strawberry", "Blueberry", "Watermelon", "Pineapple", "Mango", "Peach"]
myfruit = fruits

print(f"The list of fruits is: {fruits}")
print(f"My favorite fruit is: {myfruit}")

Notice the [0] is missing.

This is happening to me 100% of the time for at least 2 weeks (but maybe more).

Expected result

myfruit = fruits[0]

Actual result

myfruit = fruits

Variations tried (optional)

No response

App Version

3.29.3

API Provider (optional)

Google Gemini

Model Used (optional)

Gemini 2.5 pro

Roo Code Task Links (optional)

No response

Relevant logs or errors (optional)

[roomote]

I'm exploring a potential fix for the issue where Gemini strips array indices like [0] from generated code. Will open a PR to share progress.

[roomote]

After investigating this issue, I've discovered the following:

Key Findings

1. No stripping in Roo-Code: The codebase does NOT strip array indices from Gemini responses. I found a test file (grounding-sources.test.ts) that simulates stripping patterns like /\[\d+\]\s+[^:\n]+:\s+https?:\/\/[^\s\n]+/g, but these patterns are NOT actually implemented in production code.

2. Grounding sources handled separately: When Gemini provides grounding sources, they are extracted and displayed separately to users (Task.ts lines 2329-2336), but the assistant message content itself is not modified.

3. Pattern wouldn't match array indices: Even if the simulated patterns were applied (which they aren't), they require whitespace and URLs after the brackets, so fruits[0] wouldn't match.

4. Tests added: I've added tests to verify array indices are preserved and updated the existing test to clarify it's only a simulation.

Root Cause

The issue appears to be that Google Gemini's API itself is stripping array indices when grounding is enabled, interpreting [0] in code as citation markers to be removed. This is happening on Google's side before the response reaches Roo-Code.

Proposed Solutions

1. Disable grounding for code generation: When users are asking for code, grounding could be temporarily disabled to prevent this issue.

2. Report to Google: This seems to be a bug in Gemini's grounding feature that should be reported to Google.

3. Workaround in prompt: The system prompt could explicitly instruct Gemini to preserve array indices in code blocks.

Would you like me to implement option 1 (disable grounding for code-related requests) as a workaround, or would you prefer to handle this differently?

[sergedc]

Thank you @roomote , you are really good. After I disabled the grounding, the problem went away.
Are you saying that it is a bug on google's side to remove the [0] when using grounding? I doubt so....

[roomote]

I've seen your comment @sergedc. You raise a valid point - while it might be intentional behavior from Google's grounding feature (treating bracketed numbers as citation markers), it's clearly causing issues for code generation. I'll explore implementing a workaround in Roo-Code to handle this case. Let me investigate the codebase further to find the best solution.

[sergedc]

It seems to be that grounding can be helpfull for code mode, e.g. going to read some documentation. When asking ChatGPT (UI version) to code something, I always add "websearch" and that is exactly what it does: a thorough review of the documentation.

[roomote]

@sergedc I've created a PR to address this issue: #8918

The fix detects when code generation is being requested and temporarily disables grounding to prevent array indices from being stripped. The grounding feature will still work normally for non-code queries, so you get the best of both worlds.

You're right to question whether this is intentional behavior from Google - it likely is, as their grounding feature is designed to handle citations. However, it's clearly problematic for code generation, so this workaround ensures array indices are preserved while still allowing grounding for other types of queries.

All CI checks have passed. Please feel free to test the fix and provide any feedback!

[daniel-lxs]

I can confirm that disabling grounding solves the problem, I check and we don't have any logic to strip citation markers [0] out of the response so it seems to be a bug with Gemini.