Use commit sha in stack-bootstrap.yaml

Latest stack doesn't seem to support named commits such as 'master'.

Get the commit sha from `git rev-parse` and append it to the yaml file.

This doesn't fix google#391 but
goes one step further. We still get an error like:

$ stack runghc -- bootstrap.hs
Cloning 0bef8c2 from https://github.com/google/proto-lens
Unsupported tarball from /tmp/with-repo-archive189930/foo.tar: Symbolic link dest not found from proto-lens/proto-lens-imports/google to ../../google/protobuf/src/google, looking for proto-lens/../google/protobuf/src/google.
This may indicate that the source is a git archive which uses git-annex.
See commercialhaskell/stack#4579 for further information.
bootstrap.hs: readCreateProcess: stack "--stack-yaml=stack-bootstrap.yaml" "path" "--local-install-root" (exit 1): failed

bootstrap.hs

@@ -9,23 +9,35 @@
 -- Note: if this doesn't work, you may need to edit the "location" field in
 -- stack-boostrap.yaml.
 import Control.Applicative ((<$>))
-import Control.Exception (bracket_)
 import System.FilePath ((</>))
 import System.Process (callProcess, readProcess)
 
+protoRoot :: String
 protoRoot = "google/protobuf/src"
+
+protoc :: String
 protoc = "protoc"
+
+bootstrapModuleRoot :: String
 bootstrapModuleRoot = "proto-lens-protoc/app"
-useBootstrappingYaml = "--stack-yaml=stack-bootstrap.yaml"
+
+bootstrappingYaml :: FilePath
+bootstrappingYaml = "stack-bootstrap.yaml"
+
+useBootstrappingYaml :: String
+useBootstrappingYaml = "--stack-yaml=" ++ bootstrappingYaml
 
 -- Change this to build with an older version of stack.
 -- TODO: remove this after we can use stack v2 (#332).
+stack :: String
 stack = "stack"
 
 -- This should match (or at least be API-compatible with) the value of bootstrapCommit
 -- in stack-bootstrap.yaml.
+bootstrapCommit :: String
 bootstrapCommit = "master"
 
+main :: IO ()
 main = do
     -- 1. Temporarily replace the bootstrap proto bindings in proto-lens-protoc
     --    with an older version that's compatible with the bootstrap version of
@@ -35,6 +47,9 @@ main = do
     --    overwriting the previous versions.
     callProcess "git" ["checkout", bootstrapCommit, "--",
                        bootstrapModuleRoot </> "Proto"]
+    [sha] <- lines <$> readProcess "git" ["rev-parse", bootstrapCommit] ""
+    -- Append the bootstrapping commit hash to the yaml file.
+    appendFile bootstrappingYaml ("  commit: " ++ sha ++ "\n")
     [installRoot] <- lines <$> readProcess stack
                     [useBootstrappingYaml, "path", "--local-install-root"] ""
     let protocGenHaskell = installRoot </> "bin/proto-lens-protoc"

stack-bootstrap.yaml

@@ -8,10 +8,8 @@ packages:
 extra-deps:
 - ghc-source-gen-0.4.0.0
 - git: https://github.com/google/proto-lens
-  # To use the current repository:
-  # git: ../..  # stack runs 'git clone' in a subdirectory
-  # Note: this commit should match the value of bootstrapCommit in bootstrap.hs
-  commit: master
   subdirs:
   - proto-lens
   - proto-lens-runtime
+  # A line like below will be appended by bootstrap.hs.
+  # commit: 0bef8c2f3da645f068b8a26ac168c1da41608182