Regarding chau and cha contractions, what happens in -って and -んで cases?

Question

When contracting -てしまう or -でしまう to -ちゃう or -ちゃ, what happens in the -って and -んで cases?

For example, does 洗ってしまう become あらちゃう or あらっちゃう?

Similarly, does 喚んでしまわない become 喚んじまわない or 喚じまわない?

I'm trying to write a conjugator, but my Japanese is limited.

Answer 1

The rule is fairly simple. Regardless of what comes before て/で:

• てしまう contracts to ちゃう or ちまう.
• でしまう contracts to じゃう or じまう.

The character before て/で, which is often っ or ん in godan verbs, must not be removed nor changed.

All of these conjugate like an ordinary godan verb such as 使う and 合う. Note that ちまう/じまう sounds fairly rough (it almost sounds like delinquent/gang speech in fiction).

Therefore:

• 洗ってしまう → 洗っちゃう (or 洗っちまう)
• 洗ってしまわない → 洗っちゃわない (or 洗っちまわない)
• 洗ってしまった → 洗っちゃった (or 洗っちまった)
• 呼んでしまう → 呼んじゃう (or 呼んじまう)
• 呼んでしまわない → 呼んじゃわない (or 呼んじまわない)

For other godan verbs:

• 泣いてしまう → 泣いちゃう (or 泣いちまう)
• 行ってしまう → 行っちゃう (or 行っちまう)

For ichidan verbs:

• 見てしまう → 見ちゃう (or 見ちまう)
• 食べてしまう → 食べちゃう (or 食べちまう)

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This chart is helpful, too.