block for lock on second codebase open

the transcript.inplace runner seems to open the codebase for migrations,
then opens it a second time to tun the actual transcript. there seems to
be a race condition in which releasing the lock the first time doesn't
actually block for the lock to be released; and in fact it doesn't seem
to be released in time to acquire the lock the second time, and we were
seeing crashes in CI as a result.

there were a few other places where it looked like it might be fine and
good (though not necessary) to also block for the lock, but i left them
out in order to have a more surgical PR.

Author: aryairani

parser-typechecker/src/Unison/Codebase/Init.hs

@@ -49,6 +49,8 @@ data SpecifiedCodebase
 data CodebaseLockOption
   = DoLock
   | DontLock
+  | BlockUntilLock
+  deriving stock (Show)
 
 data BackupStrategy
   = -- Create a backup of the codebase in the same directory as the codebase,

parser-typechecker/src/Unison/Codebase/SqliteCodebase.hs

@@ -14,7 +14,7 @@ import Data.Either.Extra ()
 import Data.Foldable qualified as Foldable
 import Data.Map qualified as Map
 import Data.Set qualified as Set
-import System.FileLock (SharedExclusive (Exclusive), withTryFileLock)
+import System.FileLock (SharedExclusive (Exclusive), withFileLock, withTryFileLock)
 import U.Codebase.HashTags (BranchHash, CausalHash)
 import U.Codebase.Sqlite.Operations qualified as Operations
 import Unison.Codebase (Codebase, CodebasePath)
@@ -322,6 +322,12 @@ sqliteCodebase debugName root localOrRemote lockOption migrationStrategy action
         withTryFileLock (lockfilePath root) Exclusive (\_flock -> runInIO ma) <&> \case
           Nothing -> Left OpenCodebaseFileLockFailed
           Just x -> x
+      BlockUntilLock -> withRunInIO \runInIO ->
+        withTryFileLock (lockfilePath root) Exclusive (\_flock -> runInIO ma) >>= \case
+          Nothing -> do
+            liftIO (putStrLn "Waiting for codebase lock...")
+            withFileLock (lockfilePath root) Exclusive (\_flock -> runInIO ma)
+          Just x -> pure x
 
 ensureMigrated ::
   (MonadUnliftIO m) =>

unison-cli/src/Unison/Main.hs

@@ -515,7 +515,7 @@ runTranscripts' version progName transcriptDir markdownFiles = do
   and
     <$> getCodebaseOrExit
       (Just (DontCreateCodebaseWhenMissing transcriptDir))
-      SC.DoLock
+      SC.BlockUntilLock
       (SC.MigrateAutomatically SC.Backup SC.Vacuum)
       \(_, codebasePath, theCodebase) -> do
         let isTest = False