Reduce the API of proto-lens-protoc. (google#357)

Previously we exposed most of the internals as a library, with the hope
that they'd be useful for plugins (i.e. for services).  But now we're
exposing service information at the type level, and the library
continues to be unused.  Removing most of it allows us to change
the internals without requiring a major version bump.  For example,
with this change the migration to ghc-source-gen would have only
required a minor version bump.

Fixes google#347.  I think it's not feasible to completely remove the library
at this time, since we still want to share logic around module
names between proto-lens-protoc and proto-lens-setup.

Changelog.md

@@ -9,6 +9,9 @@
 - Use `ghc-source-gen` instead of `haskell-src-exts`.  Removes
   `Data.ProtoLens.Compiler.Combinators` and adds
   `Data.ProtoLens.Compiler.Definitions`.
+- Limit the exposed library to a single module
+  `Data.ProtoLens.Compiler.ModuleName`.  The other modules were not
+  used in practice, and exposed internals unnecessarily.
 
 ### Backwards-Compatible Changes
 - Fix a potential naming conflict when message types and enum values

src/Data/ProtoLens/Compiler/Plugin.hs → app/Data/ProtoLens/Compiler/Plugin.hs

@@ -14,26 +14,19 @@ module Data.ProtoLens.Compiler.Plugin
     , ProtoFile(..)
     , analyzeProtoFiles
     , collectEnvFromDeps
-    , outputFilePath
-    , moduleName
-    , moduleNameStr
     ) where
 
-import Data.Char (toUpper)
-import Data.List (foldl', intercalate)
+import Data.List (foldl')
 import qualified Data.Map.Strict as Map
 import Data.Map.Strict (Map, unions, (!))
-#if !MIN_VERSION_base(4,11,0)
-import Data.Semigroup ((<>))
-#endif
 import Data.String (fromString)
 import qualified Data.Text as T
 import Data.Text (Text)
 import Lens.Family2
 import Proto.Google.Protobuf.Descriptor (FileDescriptorProto)
-import System.FilePath (dropExtension, splitDirectories)
 
 import Data.ProtoLens.Compiler.Definitions
+import Data.ProtoLens.Compiler.ModuleName
 
 import GHC.SourceGen (ModuleNameStr, OccNameStr, RdrNameStr)
 
@@ -51,12 +44,12 @@ data ProtoFile = ProtoFile
 
 -- Given a list of FileDescriptorProtos, collect information about each file
 -- into a map of 'ProtoFile's keyed by 'ProtoFileName'.
-analyzeProtoFiles :: Text -> [FileDescriptorProto] -> Map ProtoFileName ProtoFile
-analyzeProtoFiles modulePrefix files =
+analyzeProtoFiles :: [FileDescriptorProto] -> Map ProtoFileName ProtoFile
+analyzeProtoFiles files =
     Map.fromList [ (f ^. #name, ingestFile f) | f <- files ]
   where
     filesByName = Map.fromList [(f ^. #name, f) | f <- files]
-    moduleNames = fmap (moduleName modulePrefix) filesByName
+    moduleNames = fmap fdModuleName filesByName
     -- The definitions in each input proto file, indexed by filename.
     definitionsByName = fmap collectDefinitions filesByName
     servicesByName = fmap collectServices filesByName
@@ -83,31 +76,10 @@ collectEnvFromDeps :: [ProtoFileName] -> Map ProtoFileName ProtoFile -> Env RdrN
 collectEnvFromDeps deps filesByName =
     unions $ fmap (exportedEnv . (filesByName !)) deps
 
--- | Get the output file path (for CodeGeneratorResponse.File) for a Haskell
--- ModuleName.
-outputFilePath :: String -> Text
-outputFilePath n = T.replace "." "/" (T.pack n) <> ".hs"
-
 -- | Get the Haskell 'ModuleName' corresponding to a given .proto file.
-moduleName :: Text -> FileDescriptorProto -> ModuleNameStr
-moduleName modulePrefix fd
-      = fromString $ moduleNameStr (T.unpack modulePrefix) (T.unpack $ fd ^. #name)
-
--- | Get the Haskell module name corresponding to a given .proto file.
-moduleNameStr :: String -> FilePath -> String
-moduleNameStr prefix path = fixModuleName rawModuleName
-  where
-    fixModuleName "" = ""
-    -- Characters allowed in Bazel filenames but not in module names:
-    fixModuleName ('.':c:cs) = '.' : toUpper c : fixModuleName cs
-    fixModuleName ('_':c:cs) = toUpper c : fixModuleName cs
-    fixModuleName ('-':c:cs) = toUpper c : fixModuleName cs
-    fixModuleName (c:cs) = c : fixModuleName cs
-    rawModuleName = intercalate "."
-                        . (prefix :)
-                        . splitDirectories $ dropExtension
-                        $ path
-
+fdModuleName :: FileDescriptorProto -> ModuleNameStr
+fdModuleName fd
+      = fromString $ protoModuleName (T.unpack $ fd ^. #name)
 
 -- | Given a list of .proto files (topologically sorted), determine which
 -- files' definitions are exported by which files.

app/protoc-gen-haskell.hs

@@ -78,8 +78,7 @@ makeResponse dflags prog request = let
 generateFiles :: DynFlags -> ModifyImports -> (FileDescriptorProto -> Text)
               -> [FileDescriptorProto] -> [ProtoFileName] -> [(Text, Text)]
 generateFiles dflags modifyImports header files toGenerate = let
-  modulePrefix = "Proto"
-  filesByName = analyzeProtoFiles modulePrefix files
+  filesByName = analyzeProtoFiles files
   -- The contents of the generated Haskell file for a given .proto file.
   modulesToBuild :: ProtoFile -> [CommentedModule]
   modulesToBuild f = let
@@ -92,11 +91,13 @@ generateFiles dflags modifyImports header files toGenerate = let
              (definitions f)
              (collectEnvFromDeps deps filesByName)
              (services f)
-  in [ ( outputFilePath $ showPpr dflags $ getModuleName modul
+  in [ ( moduleFilePath $ pack $ showPpr dflags (getModuleName modul)
        , header (descriptor f) <> pack (showPpr dflags modul)
        )
      | fileName <- toGenerate
      , let f = filesByName ! fileName
      , modul <- modulesToBuild f
      ]
 
+moduleFilePath :: Text -> Text
+moduleFilePath n = T.replace "." "/" n <> ".hs"

package.yaml

@@ -18,30 +18,25 @@ extra-source-files:
 
 dependencies:
   - base >= 4.9 && < 4.14
-  - containers >= 0.5 && < 0.7
-  - lens-family >= 1.2 && < 2.1
-  - proto-lens == 0.5.*
-  - text == 1.2.*
-  - ghc-source-gen == 0.3.*
-  - ghc >= 8.2 && < 8.10
-
+  - filepath >= 1.4 && < 1.6
 
 library:
   source-dirs: src
-  dependencies:
-    - filepath >= 1.4 && < 1.6
-    - pretty == 1.1.*
   exposed-modules:
-    - Data.ProtoLens.Compiler.Definitions
-    - Data.ProtoLens.Compiler.Generate
-    - Data.ProtoLens.Compiler.Generate.Commented
-    - Data.ProtoLens.Compiler.Plugin
+    - Data.ProtoLens.Compiler.ModuleName
 
 executables:
   proto-lens-protoc:
     main: protoc-gen-haskell.hs
     source-dirs: app
     dependencies:
-      - ghc-paths == 0.1.*
       - bytestring == 0.10.*
+      - containers >= 0.5 && < 0.7
+      - ghc >= 8.2 && < 8.10
+      - ghc-paths == 0.1.*
+      - ghc-source-gen == 0.3.*
+      - lens-family >= 1.2 && < 2.1
+      - pretty == 1.1.*
+      - proto-lens == 0.5.*
       - proto-lens-protoc
+      - text == 1.2.*

src/Data/ProtoLens/Compiler/ModuleName.hs

@@ -0,0 +1,24 @@
+module Data.ProtoLens.Compiler.ModuleName
+    ( protoModuleName ) where
+
+import Data.Char (toUpper)
+import Data.List (intercalate)
+import System.FilePath
+
+-- | Get the Haskell module name corresponding to a given .proto file.
+protoModuleName :: FilePath -> String
+protoModuleName path = fixModuleName rawModuleName
+  where
+    fixModuleName "" = ""
+    -- Characters allowed in Bazel filenames but not in module names:
+    fixModuleName ('.':c:cs) = '.' : toUpper c : fixModuleName cs
+    fixModuleName ('_':c:cs) = toUpper c : fixModuleName cs
+    fixModuleName ('-':c:cs) = toUpper c : fixModuleName cs
+    fixModuleName (c:cs) = c : fixModuleName cs
+    rawModuleName = intercalate "."
+                        . (prefix :)
+                        . splitDirectories $ dropExtension
+                        $ path
+
+prefix :: String
+prefix = "Proto"