CompilerPanic caused by using String[64] directly as HashMap key

[picked-a-username]

Version Information

• vyper Version (output of vyper --version): 0.2.7
• OS: OSX 10.15.6 (19G2021)
• Python Version (output of python --version): 3.6.8

What's your issue about?

Full Error:

Error compiling: test.vy
vyper.exceptions.CompilerPanic: Number of arguments mismatched: add []

This is an unhandled internal compiler error. Please create an issue on Github to notify the developers.
https://github.com/vyperlang/vyper/issues/new?template=bug.md

• what command you ran? vyper test.vy
• the code that caused the failure (see this link for help with formatting code)

struct Thing:
    name: String[64]

indexToThing: public(HashMap[uint256, Thing])
NameToStatus: public(HashMap[String[64], bool])

@external
def foo(_index: uint256):
    
    self.NameToStatus[self.indexToThing[_index].name] = True
    self.indexToThing[_index] = empty(Thing)
    

Detailed steps to reproduce the issue

Save the code above as test.vy and run vyper test.vy to reproduce the issue.

What was the result of the issue

The program failed to compile.

What the expected behaviour is

It is expected to compile successfully.

Temporary Fix

I stored self.indexToThing[_index].name in a variable and then used the variable as the key for self.NameToStatus instead of directly using self.indexToThing[_index].name
Working code:

struct Thing:
    name: String[64]

indexToThing: public(HashMap[uint256, Thing])
NameToStatus: public(HashMap[String[64], bool])


@external
def foo(_index: uint256):
    
    name: String[64] = self.indexToItem[_index].name
    self.NameToStatus[name] = True
    self.indexToThing[_index] = empty(Thing)

[iamdefinitelyahuman]

I took a closer look at this, seems you managed to find two bugs at once :)