Does this behavior persist if the lines contain something more complicated than a literal?
IIRC there’s a gotcha with coverage related to lines with a bare literal. Some related discussion: Save my from myself: Code coverage misses lines that return a literal
Of course, not. This only happens when the AST representation of the line is not the usual 3-tuple with the metadata in the middle of it. (That means, if the representation is the term itself, like numbers, atoms, lists, 2-tuples, strings, maybe others.) The problem is that it is totally realistic that one writes a single atom, or a tuple like {:error, :not_found} into a clause body. This thing should work even with very simple literals. try works, so I believe it is possible to fix with too.
The fix is based on ->, so it can’t work on if/unless. with has issues because we mark some clauses as generated to make Dialyzer happy but this will be fixed when we depend on Erlang/OTP 25. Perhaps we can do conditional compilation to have the benefits sooner.
Hi,
unfortunately this problem still exists. I totally understand the root cause of the issue (that is the missing line information in the quoted expressions), but found out that the else branch of a with special form actually has the line info in it, but coverage tools are not using it. Here is an oversimplified example (I use integers in it for two reasons: 1) ensure that no accidental line info is added, 2) make it easier to compare the Elixir code with the AST):
66 with 1 <- 2,
67 3 <- 4 do
68 5
69 else
70 6 ->
71 7
72
73 {8, 9, 10, 11, 12} ->
74 13
75
76 14 ->
77 15 + 0
78
79 _ ->
80 42
81 end
Here’s how it look like when code coverage is checked:
The <- lines are perfect. I understand why 5 (line 68) is not involved, that’s OK. But the else section looks strange. Only 15 + 0 is covered because of the + function call, not even the 5-tuple before the arrow.
Here’s the relevant part of the AST:
else: [
{:->, [line: 71, column: 9], [[6], 7]},
{:->, [line: 74, column: 26],
[[{:{}, [line: 74, column: 7], [8, 9, 10, 11, 12]}], 13]},
{:->, [line: 77, column: 10],
[[14], {:+, [line: 78, column: 12], [15, 0]}]},
{:->, [line: 80, column: 9], [[{:_, [line: 80, column: 7], nil}], 42]}
]
:-> 3-tuples have proper line metadata, but not used in coverage for some reason.{8, 9, 10, 11, 12} has line metadata on the left hand side of the arrow, still not used in coverage.Is it possible to fix this somehow?
As mentioned earlier:
There is no option besides making with raise false warnings for those using Dialyzer 
I thought we would be able to use Erlang’s maybe, but guard support is missing.