How to get Haskero to warn on non-exhaustive pattern matches

问题

I'm currently evaluating Haskero in Visual Studio Code as an alternative Haskell editor instead of Atom with Atom-Haskell. So far, Haskero seems promising, but I miss the compiler warnings I'd usually get from Atom-Haskell.

As a way to illustrate the problem, consider this simple repro:

Steps to reproduce

1. Open Visual Studio Code with Haskero already installed
2. Add a new Haskell file: Repro.hs
3. Add the following content to the file
4. Press Save

File contents:

module Repro where

foo :: Maybe a -> a
foo (Just x) = x

Expected behaviour

The editor should give a warning to the effect of:

Pattern match(es) are non-exhaustive
In an equation for `foo': Patterns not matched: Nothing

Atom-Haskell does this.

Actual behaviour

Nothing happens. The Problems view just states that:

No problems have been detected in the workspace so far.

More details

The above steps to reproduce are the simplest ones I could think of, but I see the same (lack of) behaviour when I create a full Stack project and make sure that I've run stack build intero in the root of my project directory.

My environment is:

• Windows 10 Pro x64
• Stack version 1.6.3, Git revision b27e629b8c4ce369e3b8273f04db193b060000db (5454 commits) x86_64 hpack-0.20.0
• Visual Studio Code version 1.20.0
• Haskero version 1.3.1
• Atom version 1.23.3 x64
• language-haskell version 1.17.3

回答1:

It looks like you have to tell Haskero to make any warning into a fatal error (note the -Werror flag):

"haskero.intero.ghciOptions": [
    "-Wall",
    "-Werror"
]

---

However, I can't really understand why we would have to do this, since this works out of the box:

stack ghci --with-ghc intero "--ghci-options=-Wall" --no-build --no-load

That seems to be the way Haskero launches Intero in Visual Studio Code, and in GHCi I can see the warning without passing -Werror...

---

Out of curiosity, I've tried the same with hsdev 0.3.1.2, and Sublime Haskell 91e0d29, and seems to be working straight out of the box:

Hope that helps.

来源：https://stackoverflow.com/questions/48770086/how-to-get-haskero-to-warn-on-non-exhaustive-pattern-matches