From 3b3564203ccf6087b49c1e8494d14e675fe111ac Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Dandelion=20Man=C3=A9?= <decentralion@dandelion.io>
Date: Tue, 29 May 2018 13:56:36 -0700
Subject: [PATCH] Flow: enable `//$ExpectFlowError` (#315)

As of this commit, adding the comment `//$ExpectFlowError` in flow-typed
code asserts that the next line must cause a flow error. If it does, no
error or warning is generated. If it does not, then this produces a flow
warning, which is visible to developers running `yarn flow` and
additionally causes travis to fail.

Test plan:

- As committed, `yarn travis` passes.
- I added `//$ExpectFlowError` above some line of flow-checked code which does
not currently throw an error. Afterwards, `yarn travis` failed (and a
helpful message was displayed in console on running `yarn flow`)
- I added the following bad code into one of our files:
```javascript
//$ExpectFlowError
const foo: string = 3;
```
As expected, `yarn flow` and `yarn travis` both passed.
---
 .flowconfig      |  2 ++
 config/travis.js | 10 +++++++++-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/.flowconfig b/.flowconfig
index 0d26140..ba01d69 100644
--- a/.flowconfig
+++ b/.flowconfig
@@ -8,5 +8,7 @@ flow-typed
 [lints]
 
 [options]
+suppress_comment=\\(.\\|\n\\)*\\$ExpectFlowError
+include_warnings=true
 
 [strict]
diff --git a/config/travis.js b/config/travis.js
index 1ada235..10ef36b 100644
--- a/config/travis.js
+++ b/config/travis.js
@@ -41,7 +41,15 @@ function makeTasks(mode /*: "BASIC" | "FULL" */) {
     },
     {
       id: "flow",
-      cmd: ["npm", "run", "--silent", "flow", "--", "--quiet"],
+      cmd: [
+        "npm",
+        "run",
+        "--silent",
+        "flow",
+        "--",
+        "--quiet",
+        "--max-warnings=0",
+      ],
       deps: [],
     },
     {