Test suite: a more robust way of testing the executable.

Mmny of our tests require running the pandoc
executable. This is problematic for a few different reasons.
First, cabal-install will sometimes run the test suite
after building the library but before building the executable,
which means the executable isn't in place for the tests.
One can work around that by first building, then building
and running the tests, but that's fragile.  Second,
we have to find the executable. So far, we've done that
using a function findPandoc that attempts to locate it
relative to the test executable (which can be located
using findExecutablePath).  But the logic here is delicate
and work with every combination of options.

To solve both problems, we add an `--emulate` option to
the `test-pandoc` executable.  When `--emulate` occurs
as the first argument passed to `test-pandoc`, the
program simply emulates the regular pandoc executable,
using the rest of the arguments (after `--emulate`).
Thus,

    test-pandoc --emulate -f markdown -t latex

is just like

    pandoc -f markdown -t latex

Since all the work is done by library functions,
implementing this emulation just takes a couple lines
of code and should be entirely reliable.

With this change, we can test the pandoc executable
by running the test program itself (locatable using
findExecutablePath) with the `--emulate` option.
This removes the need for the fragile `findPandoc`
step, and it means we can run our integration tests
even when we're just building the library, not the
executable.

Part of this change involved simplifying some complex
handling to set environment variables for dynamic
library paths.  I have tested a build with
`--enable-dynamic-executable`, and it works, but
further testing may be needed.

1 files changed, 12 insertions, 9 deletions

diff --git a/test/Tests/Old.hs b/test/Tests/Old.hs
index 638620a36..528388c51 100644
--- a/test/Tests/Old.hs
+++ b/test/Tests/Old.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE NoImplicitPrelude #-}
+{-# LANGUAGE TupleSections #-}
 {- |
    Module      : Tests.Old
    Copyright   : © 2006-2021 John MacFarlane
@@ -19,6 +20,7 @@ import Data.Maybe (catMaybes)
 import System.Exit
 import System.FilePath (joinPath, splitDirectories, (<.>), (</>))
 import qualified System.Environment as Env
+import System.Environment.Executable (getExecutablePath)
 import Text.Pandoc.Process (pipeProcess)
 import Test.Tasty (TestTree, testGroup)
 import Test.Tasty.Golden.Advanced (goldenTest)
@@ -322,13 +324,14 @@ testWithNormalize normalizer pandocPath testname opts inp norm =
         getActual   = do
               mldpath   <- Env.lookupEnv "LD_LIBRARY_PATH"
               mdyldpath <- Env.lookupEnv "DYLD_LIBRARY_PATH"
-              let mbDynlibDir = findDynlibDir (reverse $
-                                 splitDirectories pandocPath)
-              let dynlibEnv = [("DYLD_LIBRARY_PATH", intercalate ":" $ catMaybes [mbDynlibDir, mdyldpath])
-                              ,("LD_LIBRARY_PATH",   intercalate ":" $ catMaybes [mbDynlibDir, mldpath])]
-              let env = dynlibEnv ++
-                        [("TMP","."),("LANG","en_US.UTF-8"),("HOME", "./")]
-              (ec, out) <- pipeProcess (Just env) pandocPath options mempty
+              let env  = ("TMP",".") :
+                         ("LANG","en_US.UTF-8") :
+                         ("HOME", "./") :
+                         maybe [] ((:[]) . ("LD_LIBRARY_PATH",)) mldpath ++
+                         maybe [] ((:[]) . ("DYLD_LIBRARY_PATH",)) mdyldpath
+
+              (ec, out) <- pipeProcess (Just env) pandocPath
+                             ("--emulate":options) mempty
               if ec == ExitSuccess
                  then return $ filter (/='\r') . normalizer
                              $ UTF8.toStringLazy out
@@ -339,8 +342,8 @@ testWithNormalize normalizer pandocPath testname opts inp norm =
 
 compareValues :: FilePath -> [String] -> String -> String -> IO (Maybe String)
 compareValues norm options expected actual = do
-  pandocPath <- findPandoc
-  let cmd  = pandocPath ++ " " ++ unwords options
+  testExePath <- getExecutablePath
+  let cmd  = testExePath ++ " --emulate " ++ unwords options
   let dash = replicate 72 '-'
   let diff = getDiff (lines actual) (lines expected)
   if expected == actual