[SR-10291] Some of the error messages might require trimming

[xedin]

Previous ID	SR-10291
Radar	rdar://problem/49393677
Original Reporter	@xedin
Type	Bug

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, DiagnosticsQoI, StarterBug
Assignee	None
Priority	Medium

md5: 59ddf07a63039e0c74cd437ae791689d

Issue Description:

Consider following example:

func foo(_: UnsafePointer<Int8>?) {}
foo((1, 2, 3))

This results in:

cannot convert value of type '(Int, Int, Int)' to expected argument type 'UnsafePointer<Int8>?'

So the more elements to the tuple we add, the bigger the message is going to get.

I think it makes sense to trim contents of the tuple which has same types to something like `(Int8, ..., Int8)` to make sure that it doesn't grow too long.

[belkadan]

I'm concerned about doing this if both values are tuples and there might be a mismatch:

cannot convert value of '(Int, Float, Double, Float, Int)' to expected argument type '(Int, Float, UInt, Float, Int)'

This might not be at the top-level either; the two types might both be pointers to such tuples. Clang has a complicated Type diffing system to try to see when this is the case, but I don't know how it handles implicit conversions.

[xedin]

That's a fair point! I think we should at least handle easy cases here like - if there is a single conflicting element - mention its type and position in custom error message, otherwise try to see if types could be folded. For the nested tuples we could also probably mention them separately and note what position they were in.

[belkadan]

It's also the sort of thing we could at least have a frontend flag to turn off, if it turns out the compiler is hiding information that someone needs.

[xedin]

Sounds good!

[swift-ci]

Comment by Rajagopalan Gangadharan (JIRA)

@xedin @belkadan This seems to be an interesting task. Could I work on this? if yes could you please give some pointers that might be useful. Thank you!

[swift-ci]

Comment by Rajagopalan Gangadharan (JIRA)

If I understand this right, we should be adding a flag say truncate-type or something. If its turned on Then similar types to be grouped For eg (Int,Int,Int,Int,Float,Float,Float,Float) could be written as

(Int...,Float..) something like this?