I propose that we add `IO.error/2` which matches the signature of
`IO.warn/2`. It emits error diagnostics/messages instead of warnings and it
causes the compile step to finish with :error.
*Reasoning*
Often when building a macro you'll do some validation and `raise` an error
if something isn't right. This creates a poor experience for the person
using the macro for two reasons:
1. You can only raise one error at a time
2. You don't get a good picture of where the error is because your whole
editor turns red
You can solve both of those problems by using `IO.warn/2`. You can emit
multiple warnings in a single compile step and you can pass in a stacktrace
which gets turned into a Compiler Diagnostic that in turn, creates good
editor hints. But now the compilation succeeds and you're left in a bad
state.
I think it is useful to see multiple errors at a time because it shortens
the feedback loop. It also gives more context and can help you realize
where the root cause of your issue lies.
I think it would be useful to have a function that shared the properties of
`IO.warn/2` and `raise/1`:
- I can emit multiple messages during a single compilation run
- These messages are output as Compiler Diagnostic errors
- Invoking this function will ultimately cause the compilation step to
result in an :error
*Examples*
Today in Ecto Query, this snippet will cause the entire file to turn red
because we mistakenly used sort_by instead of order_by.
query p in Product, sort_by: p.price
Lets assume we forgot to load the :user type in this Absinthe Schema. We
have two errors but only one gets displayed. Once again, the entire editor
turns red. If instead we saw each line that referenced :user turn red it
might remind us more quickly that we forgot to call `import_types
MyApp.UserTypes`.
query name: "Query" do
field :user, :user, resolve: &MyApp.Users.get_user/3
...
field :users, list_of(:user), resolve: &MyApp.Users.list_user/3
...
end
I'm currently working on a library to create GraphQL queries. I can detect
three errors in the following snippet. Today I can only report one at a
time and am greeted with the wall of red. If I switch to `IO.warn/2` I can
report them all and see nice editor hints but my user is left with broken
code after compile.
query do
user(id: "should_be_a_number") do # wrong type for id
firstNam # misspelled, should be firstName
lastName do # lastName should not have a do...end block
name
end
end
end
*Code*
Here is a patch that adds `IO.error/2`:
https://github.com/elixir-lang/elixir/compare/master...numso:io-error
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