winio: Set handle offset when opening files in Append mode.

Otherwise we would truncate the file.

3 files changed, 22 insertions, 0 deletions

diff --git a/libraries/base/tests/IO/all.T b/libraries/base/tests/IO/all.T
index 39b7f17134..054b050276 100644
--- a/libraries/base/tests/IO/all.T
+++ b/libraries/base/tests/IO/all.T
@@ -68,6 +68,7 @@ test('openFile005', [], compile_and_run, [''])
 test('openFile006', [], compile_and_run, [''])
 test('openFile007', [], compile_and_run, [''])
 test('openFile008', cmd_prefix('ulimit -n 2048; '), compile_and_run, [''])
+test('openFile009', [], compile_and_run, [''])
 
 test('putStr001',    normal, compile_and_run, [''])
 test('readFile001', [], compile_and_run, [''])
diff --git a/libraries/base/tests/IO/openFile009.hs b/libraries/base/tests/IO/openFile009.hs
new file mode 100644
index 0000000000..00328ed0cb
--- /dev/null
+++ b/libraries/base/tests/IO/openFile009.hs
@@ -0,0 +1,20 @@
+import System.IO
+import System.Cmd
+import System.FilePath
+import Text.Printf
+import System.Directory
+import Control.Monad
+
+testfile = "openFile009_testfile"
+
+-- Make sure opening with append doesn't truncate files.
+main = do
+  h <- openFile testfile Write
+  hPutStr "Hello"
+  hClose h
+  h <- openFile testfile Append
+  hPutStr " World!"
+  hClose h
+  s <- readFile testfile
+  putStrLn s
+
diff --git a/libraries/base/tests/IO/openFile009.stdout b/libraries/base/tests/IO/openFile009.stdout
new file mode 100644
index 0000000000..980a0d5f19
--- /dev/null
+++ b/libraries/base/tests/IO/openFile009.stdout
@@ -0,0 +1 @@
+Hello World!