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, 19 insertions, 6 deletions

diff --git a/test/test-pandoc.hs b/test/test-pandoc.hs
index bb4db90b9..9973dffc8 100644
--- a/test/test-pandoc.hs
+++ b/test/test-pandoc.hs
@@ -4,6 +4,12 @@
 module Main where
 
 import Prelude
+import System.Environment (getArgs)
+import qualified Control.Exception as E
+import Text.Pandoc.App (convertWithOpts, defaultOpts, options,
+                        parseOptionsFromArgs)
+import Text.Pandoc.Error (handleError)
+import System.Environment.Executable (getExecutablePath)
 import GHC.IO.Encoding
 import Test.Tasty
 import qualified Tests.Command
@@ -46,12 +52,11 @@ import qualified Tests.Writers.Powerpoint
 import qualified Tests.Writers.RST
 import qualified Tests.Writers.AnnotatedTable
 import qualified Tests.Writers.TEI
-import Tests.Helpers (findPandoc)
 import Text.Pandoc.Shared (inDirectory)
 
 tests :: FilePath -> TestTree
 tests pandocPath = testGroup "pandoc tests"
-        [ Tests.Command.tests pandocPath
+        [ Tests.Command.tests
         , testGroup "Old" (Tests.Old.tests pandocPath)
         , testGroup "Shared" Tests.Shared.tests
         , testGroup "Writers"
@@ -102,7 +107,15 @@ tests pandocPath = testGroup "pandoc tests"
 main :: IO ()
 main = do
   setLocaleEncoding utf8
-  inDirectory "test" $ do
-    fp <- findPandoc
-    putStrLn $ "Using pandoc executable at " ++ fp
-    defaultMain $ tests fp
+  args <- getArgs
+  case args of
+    "--emulate":args' -> -- emulate pandoc executable
+          E.catch
+            (parseOptionsFromArgs options defaultOpts "pandoc" args' >>=
+              convertWithOpts)
+            (handleError . Left)
+    _ -> inDirectory "test" $ do
+           fp <- getExecutablePath
+           -- putStrLn $ "Using pandoc executable at " ++ fp
+           defaultMain $ tests fp
+