opencv@2 patch has incorrect checksum

[fxcoudert]

While trying to build opencv@2 from source for Mojave bottling #28817, I realized that:

==> Downloading https://github.com/opencv/opencv/archive/2.4.13.6.tar.gz
Already downloaded: /Users/brew/Library/Caches/Homebrew/opencv@2--2.4.13.6.tar.gz
==> Verifying opencv@2--2.4.13.6.tar.gz checksum
tar xf /Users/brew/Library/Caches/Homebrew/opencv@2--2.4.13.6.tar.gz -C /private/tmp/d20180826-98631-itzc32
cp -pR /private/tmp/d20180826-98631-itzc32/opencv-2.4.13.6/. /private/tmp/opencv@2-20180826-98631-b1uckx/opencv-2.4.13.6
Error: SHA256 mismatch
Expected: 7e33c5c009aea0798cd9bd3edb0f7a2122a9f3b2a962977e53a0fccd55e1db40
Actual: c60be5bc53bc8964550c0a2467a41e391c730fb090219954a2cd8d9a54a1a5a7
Archive: /Users/brew/Library/Caches/Homebrew/opencv@2--patch--7e33c5c009aea0798cd9bd3edb0f7a2122a9f3b2a962977e53a0fccd55e1db40.patch
To retry an incomplete download, remove the file above.

[michiyosony]

I am also experiencing this.
> brew install opencv@2

==> Downloading https://github.com/opencv/opencv/archive/2.4.13.6.tar.gz
==> Downloading from https://codeload.github.com/opencv/opencv/tar.gz/2.4.13.6
######################################################################## 100.0%
==> Downloading https://github.com/opencv/opencv/commit/99091a62463.patch?full_index=1
######################################################################## 100.0%
Error: SHA256 mismatch
Expected: 7e33c5c009aea0798cd9bd3edb0f7a2122a9f3b2a962977e53a0fccd55e1db40
Actual: c60be5bc53bc8964550c0a2467a41e391c730fb090219954a2cd8d9a54a1a5a7
Archive: /Users/michiyosony/Library/Caches/Homebrew/downloads/fa7f8f61c7d587deff84ccc28eba3594a5f7eb2f4b81ed5c5ccc037d590b4319--99091a62463.patch
To retry an incomplete download, remove the file above.

Removing /Users/michiyosony/Library/Caches/Homebrew/downloads/fa7f8f61c7d587deff84ccc28eba3594a5f7eb2f4b81ed5c5ccc037d590b4319--99091a62463.patch and retrying the command does not fix the issue.

[hy9be]

Exactly the same issue.

A quick (but maybe harmful) fix is to run brew edit opencv@2, and change the SHA256 string into the "Actual" string above: https://github.com/Homebrew/homebrew-core/blob/master/Formula/opencv%402.rb#L36

[michiyosony]

Interestingly, I did not get this error when trying brew install opencv@2 on a different computer.