Use the ghc api to get imports

README.md

@@ -76,7 +76,6 @@ stack_snapshot(
     name = "stackage",
     packages = [
         "aeson",
-        "parsec",
     ],
     # Most snapshots of your choice might do
     snapshot = "lts-18.1",

WORKSPACE

@@ -51,7 +51,6 @@ stack_snapshot(
     packages = [
         "aeson",
         "hspec",
-        "parsec",
         "string-qq",
         "tasty",
         "tasty-discover",

defs.bzl

@@ -7,10 +7,8 @@ def _gazelle_haskell_modules_dependencies_impl(repository_ctx):
 package(default_visibility = ["//visibility:public"])
 
 alias(name="aeson", actual="{aeson}")
-alias(name="parsec", actual="{parsec}")
         '''.format(
             aeson = repository_ctx.attr.aeson,
-            parsec = repository_ctx.attr.parsec,
         ),
         executable = False,
     )
@@ -20,7 +18,6 @@ _gazelle_haskell_modules_dependencies = repository_rule(
     local = True,
     attrs = {
         "aeson": attr.label(default = "@stackage//:aeson"),
-        "parsec": attr.label(default = "@stackage//:parsec"),
     },
 )
 
@@ -41,7 +38,6 @@ def gazelle_haskell_modules_dependencies(**kargs):
       # Dependencies overriden
       gazelle_haskell_modules_dependencies(
           aeson = "@someother//:some-other-aeson",
-          parsec = "@someother//:parsec",
       )
 
       ```

example/WORKSPACE

@@ -56,8 +56,8 @@ stack_snapshot(
     packages = [
         "aeson",
         "base",
+        "ghc-paths",
         "inspection-testing",
-        "parsec",
         "tasty",
         "tasty-discover",
         "tasty-hunit",

example/package-a/app/Main.hs

@@ -1,10 +1,20 @@
 {-# LANGUAGE CPP #-}
+{-# LANGUAGE PatternSynonyms #-}
+{-# LANGUAGE ExplicitNamespaces #-}
+{-# LANGUAGE MagicHash #-}
 module Main where
 
 #define a_multiline macro \
   a second line of the macro
 import NonModulesLib (nonModulesLib)
-import PackageA.Other.C()
+import PackageA.Other.C(type DataC, DataC(DataC), pattern PatTrue)
+import GHC.Exts (Int(..), Int#)
 
 main :: IO ()
-main = putStrLn $ "Hello, Haskell! " ++ show nonModulesLib
+main = do
+  let
+    dataC :: DataC
+    dataC = DataC PatTrue
+    int# :: Int#
+    int# = case 1 of I# i -> i
+  putStrLn $ "Hello, Haskell! " ++ show nonModulesLib ++ show dataC ++ show (I# int#)

example/package-a/app/PackageA/Other/C.hs

@@ -1,3 +1,10 @@
+{-# LANGUAGE PatternSynonyms #-}
 module PackageA.Other.C where
 
 import PackageA.Exposed.A()
+
+data DataC = DataC Bool
+  deriving Show
+
+pattern PatTrue :: Bool
+pattern PatTrue = True

gazelle_haskell_modules/rule_generation.go

@@ -1,6 +1,7 @@
 package gazelle_haskell_modules
 
 import (
+	"bytes"
 	"encoding/json"
 	"fmt"
 	"io/fs"
@@ -151,15 +152,37 @@ func haskellModulesToModuleData(moduleFiles []string) []*ModuleData {
 	cmd := exec.Command(himportscan)
 
 	cmd.Stdin = strings.NewReader(strings.Join(moduleFiles, "\n"))
-	out, err := cmd.CombinedOutput()
+
+	var stdout bytes.Buffer
+	cmd.Stdout = &stdout
+
+	var stderr strings.Builder
+	cmd.Stderr = &stderr
+
+	err = cmd.Start()
 	if err != nil {
-		log.Printf("%s", out)
-		log.Fatal(err)
+		log.Fatalf("himportscan failed to start %v", err)
 	}
+
+	err = cmd.Wait()
+	stdoutBytes := stdout.Bytes()
+	stderrString := stderr.String()
+
+	if err != nil {
+		fmt.Printf("%s\n", stdout.Bytes())
+		fmt.Printf("%s\n", stderrString)
+		log.Fatalf("himportscan exited unsuccessfully %v\n", err)
+	}
+
+	// print stderr so if himportscan generates some stderr but doesn't fail the user might see useful output
+	if stderrString != "" {
+		log.Printf("%s\n", stderrString)
+	}
+
 	var modDatas []*ModuleData
-	err = json.Unmarshal(out, &modDatas)
+	err = json.Unmarshal(stdoutBytes, &modDatas)
 	if err != nil {
-		log.Printf("Incorrect json: %s\n", out)
+		log.Printf("Incorrect json: %s\n", stdoutBytes)
 		log.Fatal(err)
 	}
 	return modDatas

himportscan/BUILD.bazel

@@ -12,10 +12,16 @@ haskell_toolchain_library(name = "base")
 
 haskell_toolchain_library(name = "bytestring")
 
+haskell_toolchain_library(name = "containers")
+
 haskell_toolchain_library(name = "directory")
 
 haskell_toolchain_library(name = "ghc")
 
+# Needed for GHC.LanguageExtensions.
+# You can probably revisit this when changing ghc versions.
+haskell_toolchain_library(name = "ghc-boot")
+
 haskell_toolchain_library(name = "text")
 
 haskell_library(
@@ -28,11 +34,12 @@ haskell_library(
     deps = [
         ":base",
         ":bytestring",
+        ":containers",
         ":directory",
         ":ghc",
+        ":ghc-boot",
         ":text",
         "@io_tweag_gazelle_haskell_modules_deps//:aeson",
-        "@io_tweag_gazelle_haskell_modules_deps//:parsec",
     ],
 )
 
@@ -46,6 +53,7 @@ haskell_binary(
     deps = [
         ":base",
         ":bytestring",
+        ":containers",
         ":ghc",
         ":himportscan-library",
         ":text",
@@ -66,6 +74,7 @@ haskell_test(
     ],
     deps = [
         ":base",
+        ":containers",
         ":himportscan-library",
         ":text",
         "@stackage//:hspec",

himportscan/exe/Main.hs

@@ -2,10 +2,10 @@
 {-# LANGUAGE OverloadedStrings #-}
 module Main where
 
-import HImportScan.ImportScanner (ScannedImports, scanImportsFromFile)
 import qualified Data.Aeson as Aeson
 import qualified Data.ByteString.Lazy.Char8 as ByteString.Lazy
 import Data.Maybe (catMaybes)
+import HImportScan.ImportScanner (ScannedImports, scanImportsFromFile)
 
 main :: IO ()
 main = do

himportscan/src/HImportScan/GHC.hs

@@ -1,8 +1,24 @@
 -- | A module abstracting the provenance of GHC API names
 module HImportScan.GHC(module X) where
 
+import DynFlags as X (DynFlags, defaultDynFlags, xopt_set, xopt_unset)
 import EnumSet as X (empty, fromList)
-import FastString as X (mkFastString, unpackFS)
+import ErrUtils as X (printBagOfErrors)
+import FastString as X (FastString, mkFastString, bytesFS)
+import GHC as X (runGhc, getSessionDynFlags)
+import GHC.LanguageExtensions as X
+  (Extension
+    ( ImportQualifiedPost
+    , PackageImports
+    , TemplateHaskell
+    , ImplicitPrelude
+    , PatternSynonyms
+    , ExplicitNamespaces
+    , MagicHash
+    )
+  )
+import HeaderInfo as X (getOptions, getImports)
+import HscTypes as X (mkSrcErr)
 import Lexer as X
   ( ParseResult(..)
   , Token(..)
@@ -11,6 +27,7 @@ import Lexer as X
   , mkParserFlags'
   , mkPStatePure, unP
   )
+import Module as X (ModuleName, moduleNameString)
 import SrcLoc as X
   ( Located
   , RealSrcLoc
@@ -22,4 +39,4 @@ import SrcLoc as X
   , srcSpanStart
   , unLoc
   )
-import StringBuffer as X (StringBuffer(StringBuffer))
+import StringBuffer as X (StringBuffer(StringBuffer), stringToStringBuffer)

himportscan/src/HImportScan/GHC/Settings.hs

@@ -0,0 +1,50 @@
+-- Copyright (c) 2020, Shayne Fletcher. All rights reserved.
+-- SPDX-License-Identifier: BSD-3-Clause.
+
+{-# OPTIONS_GHC -Wno-missing-fields #-}
+{-# OPTIONS_GHC -Wno-name-shadowing #-}
+
+-- This file is a single code path copied over from https://hackage.haskell.org/package/ghc-lib-parser-ex-8.10.0.24/docs/src/Language.Haskell.GhclibParserEx.GHC.Settings.Config.html
+-- TODO[GL]: We can get rid of this file once we only support >=9.2, as ParserOpts are much smaller there.
+module HImportScan.GHC.Settings(
+    fakeSettings
+  , fakeLlvmConfig
+  )
+where
+
+import Config
+import DynFlags
+import Fingerprint
+import GHC.Platform
+import ToolSettings
+
+fakeSettings :: Settings
+fakeSettings = Settings
+  { sGhcNameVersion=ghcNameVersion
+  , sFileSettings=fileSettings
+  , sTargetPlatform=platform
+  , sPlatformMisc=platformMisc
+  , sPlatformConstants=platformConstants
+  , sToolSettings=toolSettings
+  }
+  where
+    toolSettings = ToolSettings {
+      toolSettings_opt_P_fingerprint=fingerprint0
+      }
+    fileSettings = FileSettings {}
+    platformMisc = PlatformMisc {}
+    ghcNameVersion =
+      GhcNameVersion{ghcNameVersion_programName="ghc"
+                    ,ghcNameVersion_projectVersion=cProjectVersion
+                    }
+    platform =
+      Platform{
+        platformWordSize=PW8
+      , platformMini=PlatformMini {platformMini_arch=ArchUnknown, platformMini_os=OSUnknown}
+      , platformUnregisterised=True
+      }
+    platformConstants =
+      PlatformConstants{pc_DYNAMIC_BY_DEFAULT=False,pc_WORD_SIZE=8}
+
+fakeLlvmConfig :: LlvmConfig
+fakeLlvmConfig = LlvmConfig [] []