fix: avoid duplicate WETH in swap path when input/output is WETH (closes #363) - #459

Greptile Summary

This PR fixes the IDENTICAL_ADDRESSES router revert in Uniswap v2 token-to-token swaps when either the input or output token is WETH. Previously, both _token_to_token_swap_input and _token_to_token_swap_output unconditionally built a three-hop path [input, WETH, output], which collapses to [WETH, WETH, ...] or [..., WETH, WETH] when one side is already WETH.

• _token_to_token_swap_input: Now uses a direct two-hop path [input, output] when either token is WETH, correctly using is_same_address() for comparison.
• _token_to_token_swap_output: Same guard is applied with swapTokensForExactTokens, and the price functions already delegated to the two-hop ETH/WETH path — so the swap path and quote path are now consistent.

Confidence Score: 5/5

Safe to merge. Both swap functions now correctly skip the redundant WETH intermediate hop when input or output is already WETH.

The two-line guard added to each function uses the codebase-standard is_same_address() helper for address comparison, is consistent with how the existing price-query functions already route WETH tokens, and correctly aligns the swap path with the quote path in both the exact-input and exact-output code paths.

No files require special attention.

Important Files Changed

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[make_trade or make_trade_output] --> B{input or output is ETH_ADDRESS?}
    B -- Yes --> C[Raise ValueError]
    B -- No --> D{Uniswap version?}
    D -- v2 --> E{input or output token is WETH?}
    E -- Yes --> F["path = direct 2-hop: input to output"]
    E -- No --> G["path = 3-hop: input to WETH to output"]
    F --> H[swapExactTokensForTokens or swapTokensForExactTokens]
    G --> H
    D -- v3 --> I[exactInputSingle or exactOutputSingle]
    D -- v1 --> J[tokenToTokenSwapInput or tokenToTokenSwapOutput]

_{Reviews (3): Last reviewed commit: "fix: use is_same_address() for WETH comp..." | Re-trigger Greptile}

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.21%. Comparing base (f5a9e86) to head (c2e0aae).
⚠️ Report is 4 commits behind head on master.

@@             Coverage Diff             @@
##           master     #459       +/-   ##
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+ Coverage   60.52%   73.21%   +12.69%     
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  Files          11       12        +1     
  Lines        1074     2315     +1241     
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+ Hits          650     1695     +1045     
- Misses        424      620      +196     

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