Move purescript-cst to a bazel rule

We want to work around an issue with packages not at the top-level.

It looks as though there's some issue in the newer versions of
`rules_haskell` for Haskell packages that aren't at the top-level. This
comment gives an overview of the problem:
tweag/rules_haskell#1392 (comment).
To paraphrase, Haskell packages in a sub-directory don't really work
with `stack ls dependencies json` at the moment.

Since we want to update `rules_haskell` to a newer version, we need to
address this. We can make this change now without updating the version
so that the version bump of `rules_haskell` has a smaller diff.

In all likelihood, this issue will be fixed at some point. Haskell
packages in a sub-directory are fairly common. Until that day, we follow
most of the workaround laid out in that GitHub issue: pull in the
package as a `bazel` `http_archive` rule, point `stack_snapshot` to the
package as a `vendored_package`.

The part we do a bit differently is not stripping down to the
sub-directory. Instead, we treat the whole archive as one thing and
locate the files based on where they live from the top-level. We take
this approach primarily because we're going to pull in both
`purescript-ast` and `purescript-cst`.

Since the commit we're using doesn't have a
`lib/purescript-cst/purescript-cst.cabal` file, we have to patch it to
add that.

WORKSPACE.bazel

@@ -71,6 +71,23 @@ http_archive(
         "https://mirror.bazel.build/github.com/bazelbuild/rules_pkg/releases/download/0.2.5/rules_pkg-0.2.5.tar.gz",
     ],
 )
+
+http_archive(
+    name = "purescript_cst",
+    build_file = "//third_party/purescript-cst:purescript-cst.BUILD",
+    patch_args = [
+        "-p1",
+    ],
+    patches = [
+        "//third_party/purescript-cst:purescript-cst-cabal-file.patch",
+    ],
+    strip_prefix = "purescript-81909a9585b00bc99cc47c7959fbc5ae2e1ff285/lib/purescript-cst",
+    sha256 = "f2d685b754d93328fd2d175af0748f6f3bce7335c5d14157427876df38b566c3",
+    urls = [
+        "https://github.com/joneshf/purescript/archive/81909a9585b00bc99cc47c7959fbc5ae2e1ff285.zip",
+    ],
+)
+
 # Dependencies
 
 load(
@@ -137,14 +154,29 @@ stack_snapshot(
     local_snapshot = "//:snapshot.yaml",
     name = "stackage",
     packages = [
+        # our dependencies
         "componentm",
         "optparse-applicative",
         "pathwalk",
-        "purescript-cst",
         "rio",
+        # `purescript-cst` dependencies
+        # These have to be here so the `//third_party/purescript:purescript-cst` package can pick them up.
+        # If we ever can get rid of the `//third_party/purescript:purescript-cst` package,
+        # we can remove these dependencies
+        "array",
+        "base",
+        "containers",
+        "dlist",
+        "purescript-ast",
+        "scientific",
+        "semigroups",
+        "text",
     ],
     tools = [
         "@alex",
         "@happy",
     ],
+    vendored_packages = {
+        "purescript-cst": "@purescript_cst//:purescript-cst",
+    },
 )

snapshot.yaml

@@ -9,5 +9,4 @@ packages:
     commit: 81909a9585b00bc99cc47c7959fbc5ae2e1ff285
     subdirs:
       - lib/purescript-ast
-      - lib/purescript-cst
 resolver: lts-13.26

third_party/purescript-cst/purescript-cst-cabal-file.patch

@@ -0,0 +1,110 @@
+diff --git a/purescript-cst.cabal b/purescript-cst.cabal
+new file mode 100644
+index 00000000..dbb1ed9b
+--- /dev/null
++++ b/purescript-cst.cabal
+@@ -0,0 +1,104 @@
++cabal-version: 1.12
++
++-- This file has been generated from package.yaml by hpack version 0.31.1.
++--
++-- see: https://github.com/sol/hpack
++--
++-- hash: ff73e382fe3eaea97d6533a6b3512e14ec9eae7888720be48ae9f929e59cd733
++
++name:           purescript-cst
++version:        0.13.6
++synopsis:       PureScript Programming Language Concrete Syntax Tree
++description:    The surface syntax of the PureScript Programming Language.
++category:       Language
++stability:      experimental
++homepage:       http://www.purescript.org/
++bug-reports:    https://github.com/purescript/purescript/issues
++author:         Phil Freeman <paf31@cantab.net>
++maintainer:     Gary Burgess <gary.burgess@gmail.com>, Hardy Jones <jones3.hardy@gmail.com>, Harry Garrood <harry@garrood.me>, Christoph Hegemann <christoph.hegemann1337@gmail.com>, Liam Goodacre <goodacre.liam@gmail.com>, Nathan Faubion <nathan@n-son.com>
++
++copyright:      (c) 2013-17 Phil Freeman, (c) 2014-19 Gary Burgess, (c) other contributors (see CONTRIBUTORS.md)
++license:        BSD3
++license-file:   LICENSE
++build-type:     Simple
++extra-source-files:
++    tests/purs/layout/AdoIn.purs
++    tests/purs/layout/CaseGuards.purs
++    tests/purs/layout/CaseWhere.purs
++    tests/purs/layout/ClassHead.purs
++    tests/purs/layout/Commas.purs
++    tests/purs/layout/Delimiter.purs
++    tests/purs/layout/DoLet.purs
++    tests/purs/layout/DoOperator.purs
++    tests/purs/layout/DoWhere.purs
++    tests/purs/layout/IfThenElseDo.purs
++    tests/purs/layout/InstanceChainElse.purs
++    tests/purs/layout/LetGuards.purs
++    README.md
++
++source-repository head
++  type: git
++  location: https://github.com/purescript/purescript
++
++library
++  exposed-modules:
++      Language.PureScript.CST.Convert
++      Language.PureScript.CST.Errors
++      Language.PureScript.CST.Layout
++      Language.PureScript.CST.Lexer
++      Language.PureScript.CST.Monad
++      Language.PureScript.CST.Parser
++      Language.PureScript.CST.Positions
++      Language.PureScript.CST.Print
++      Language.PureScript.CST.Traversals
++      Language.PureScript.CST.Traversals.Type
++      Language.PureScript.CST.Types
++      Language.PureScript.CST.Utils
++  other-modules:
++      Paths_purescript_cst
++  hs-source-dirs:
++      src
++  default-extensions: ConstraintKinds DataKinds DeriveFunctor DeriveFoldable DeriveTraversable DeriveGeneric DerivingStrategies EmptyDataDecls FlexibleContexts KindSignatures LambdaCase MultiParamTypeClasses NoImplicitPrelude PatternGuards PatternSynonyms RankNTypes RecordWildCards OverloadedStrings ScopedTypeVariables TupleSections ViewPatterns
++  ghc-options: -Wall -O2
++  build-tools:
++      happy ==1.19.9
++  build-depends:
++      array
++    , base >=4.11 && <4.13
++    , containers
++    , dlist
++    , purescript-ast
++    , scientific >=0.3.4.9 && <0.4
++    , semigroups >=0.16.2 && <0.19
++    , text
++  default-language: Haskell2010
++
++test-suite tests
++  type: exitcode-stdio-1.0
++  main-is: Main.hs
++  other-modules:
++      TestCst
++      Paths_purescript_cst
++  hs-source-dirs:
++      tests
++  default-extensions: NoImplicitPrelude LambdaCase OverloadedStrings
++  ghc-options: -Wall
++  build-tools:
++      happy ==1.19.9
++  build-depends:
++      array
++    , base >=4.11 && <4.13
++    , base-compat >=0.6.0
++    , bytestring
++    , containers
++    , dlist
++    , filepath
++    , purescript-ast
++    , purescript-cst
++    , scientific >=0.3.4.9 && <0.4
++    , semigroups >=0.16.2 && <0.19
++    , tasty
++    , tasty-golden
++    , tasty-quickcheck
++    , text
++  default-language: Haskell2010

third_party/purescript-cst/purescript-cst.BUILD

@@ -0,0 +1,24 @@
+load(
+    "@rules_haskell//haskell:cabal.bzl",
+    "haskell_cabal_library",
+)
+
+load(
+    "@stackage//:packages.bzl",
+    "packages",
+)
+
+haskell_cabal_library(
+    name = "purescript-cst",
+    deps = packages["purescript-cst"].deps,
+    srcs = glob([
+        "**",
+    ]),
+    tools = [
+        "@happy//:happy",
+    ],
+    version = packages["purescript-cst"].version,
+    visibility = [
+        "//visibility:public",
+    ],
+)