Recursive rule when copying only some files

[yogsototh]

Edit: I tried with 0.19 and it seems I have the error message everytime. I am pretty sure I misused shake :). Still there might be some underlying issue. So I'll let you close it.

While I was trying to use shake to generate a static website I stumble upon this strange behavior.
For me it looks like a bug.
So the here is a self-contained way to reproduce the problem:

{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE NoImplicitPrelude #-}

import           Protolude

import           Development.Shake
import           Development.Shake.Command
import           Development.Shake.FilePath
import           Development.Shake.Util

main :: IO ()
main = shakeArgs shOpts buildRules
  where
    shOpts =
      shakeOptions
      { shakeVerbosity  = Chatty
      , shakeLintInside = ["\\"]
      }


siteDir :: FilePath
siteDir  = "_site"

optimDir :: FilePath
optimDir = "_optim"


build :: FilePath -> FilePath
build = (</>) siteDir

copy :: FilePath -> Action ()
copy out = do
  let src = "src" </> (dropDirectory1 out)
  copyFileChanged src out

cleanRule :: Rules ()
cleanRule =
  phony "clean" $ do
    putInfo "Cleaning files in _site and _optim"
    forM_ [siteDir,optimDir] $ flip removeFilesAfter ["//*"]

buildRules :: Rules ()
buildRules = do
  cleanRule
  build "//*" %> copy

And my build.sh file:

#!/bin/sh
mkdir -p _shake
ghc --make Shakefile.hs -rtsopts -threaded -with-rtsopts=-I0 -outputdir=_shake -o _shake/build && _shake/build "$@"

And then I try to execute

> ./build.sh clean
[1 of 1] Compiling Main             ( Shakefile.hs, _shake/Main.o )
Linking _shake/build ...
# clean
Cleaning files in _site and _optim
Will remove //* from _site
Will remove //* from _optim
Build completed in 0.00s

work as expected

> ./build.sh _site/posts/0010-Haskell-Now/index.org
# _site/posts/0010-Haskell-Now/index.org
Copying from src/posts/0010-Haskell-Now/index.org to _site/posts/0010-Haskell-Now/index.org
Build completed in 0.00s

also copy as expected.
But when trying on .hs files or .jpg files:

> ./build.sh _site/posts/0010-Haskell-Now/list.hs
# _site/posts/0010-Haskell-Now/list.hs
# src/posts/0010-Haskell-Now/list.hs
Error when running Shake build system:
  at want, called at src/Development/Shake/Internal/Args.hs:83:69 in shake-0.18.5-8T3hsb7Jhgk1bvj5gpap6X:Development.Shake.Internal.Args
* Depends on: _site/posts/0010-Haskell-Now/list.hs
  at copyFileChanged, called at Shakefile.hs:34:3 in main:Main
  at need, called at src/Development/Shake/Internal/Derived.hs:104:5 in shake-0.18.5-8T3hsb7Jhgk1bvj5gpap6X:Development.Shake.Internal.Derived
* Depends on: src/posts/0010-Haskell-Now/list.hs
  at copyFileChanged, called at Shakefile.hs:34:3 in main:Main
  at need, called at src/Development/Shake/Internal/Derived.hs:104:5 in shake-0.18.5-8T3hsb7Jhgk1bvj5gpap6X:Development.Shake.Internal.Derived
* Depends on: src/posts/0010-Haskell-Now/list.hs
* Raised the exception:
Build system error - recursion detected:
  Key type:   FileQ
  Key value:  src/posts/0010-Haskell-Now/list.hs
Rules may not be recursive

Edits:

• the same problem occurs if I use copyFile' instead of copyFileChanged.
• if that can help my shell.nix:

{ pkgs ? import (fetchTarball https://github.com/NixOS/nixpkgs/archive/20.03.tar.gz) {} }:
let
  pkgs1909 = import (fetchTarball https://github.com/NixOS/nixpkgs/archive/19.09.tar.gz) {};
  haskellDeps = ps : with ps; [
    shake
    pandoc
    data-default
    protolude
    pkgs1909.haskellPackages.sws
    stache
  ];
  ghc = pkgs.haskellPackages.ghcWithPackages haskellDeps;
in
pkgs.mkShell {
    buildInputs = with pkgs;
      [ cacert
        coreutils
        html-xml-utils
        zsh
        perl
        perlPackages.URI
        minify
        niv
        ghc
        git
        direnv
        haskellPackages.shake
      ];
  }

[ndmitchell]

Ah, I know what the issue is! You are using // style escapes. The issue with them is that:

`"_site" </> "//*"

Gives //* because </> is documented to return the second component if it is already absolute. You can fix it by moving to the new-style file patterns, writing:

`"_site" </> "**"

Which means the same thing. The plan is to slowly deprecate // - I should follow up on that plan as its a horrible default because its so easy to get wrong with </>.

[yogsototh]

Ah thanks a lot! Yes, I somehow made it work with more complex rules but after a few changes, I got that message again.

Also thanks for all your hard work! I love to use hlint, hoogle and ghcid, and I'm starting to love to use shake now :)