[m-rev.] for review: fix bug #407: Exception.getMessage can return null

[Julien Fischer]

For review by Peter.

-----------------------

Fix bug #407: Exception.getMessage can return null.

library/io.m:
     Add a new wrapper method throw_io_error, that checks whether
     its argument is null and, if so, converts into into a string
     before calling ML_throw_io_error.

     Check whether the Exception.getMessage returns null in a few
     spots and return a string instead.  (Other uses of getMessage
     occur in string concatenation expressions where null will
     automatically be converted into a string.)

Julien.

diff --git a/library/io.m b/library/io.m
index 1fdec3a..3e7496c 100644
--- a/library/io.m
+++ b/library/io.m
@@ -4118,7 +4118,7 @@ compare_file_id(Result, FileId1, FileId2) :-
      compare_file_id_2(_Res::out, _FileId1::in, _FileId2::in),
      [will_not_call_mercury, promise_pure, thread_safe],
  "
-    io.ML_throw_io_error(""File IDs are not supported by Java."");
+    io.throw_io_error(""File IDs are not supported by Java."");
  ").

  :- pragma foreign_proc("Erlang",
@@ -6205,7 +6205,7 @@ int             ML_fprintf(MercuryFilePtr mf, const char *format, ...);
              try {
                  put(c);
              } catch (java.io.IOException e) {
-                io.ML_throw_io_error(e.getMessage());
+                io.throw_io_error(e.getMessage());
              }
          }

@@ -6231,7 +6231,7 @@ int             ML_fprintf(MercuryFilePtr mf, const char *format, ...);
              try {
                  write(s);
              } catch (java.io.IOException e) {
-                io.ML_throw_io_error(e.getMessage());
+                io.throw_io_error(e.getMessage());
              }
          }

@@ -6245,7 +6245,7 @@ int             ML_fprintf(MercuryFilePtr mf, const char *format, ...);
              try {
                  flush();
              } catch (java.io.IOException e) {
-                io.ML_throw_io_error(e.getMessage());
+                io.throw_io_error(e.getMessage());
              }
          }

@@ -6393,7 +6393,7 @@ int             ML_fprintf(MercuryFilePtr mf, const char *format, ...);
              try {
                  put(b);
              } catch (java.io.IOException e) {
-                io.ML_throw_io_error(e.getMessage());
+                io.throw_io_error(e.getMessage());
              }
          }

@@ -6411,7 +6411,7 @@ int             ML_fprintf(MercuryFilePtr mf, const char *format, ...);
              try {
                  write(s);
              } catch (java.io.IOException e) {
-                io.ML_throw_io_error(e.getMessage());
+                io.throw_io_error(e.getMessage());
              }
          }

@@ -6425,7 +6425,7 @@ int             ML_fprintf(MercuryFilePtr mf, const char *format, ...);
              try {
                  flush();
              } catch (java.io.IOException e) {
-                io.ML_throw_io_error(e.getMessage());
+                io.throw_io_error(e.getMessage());
              }
          }

@@ -7220,7 +7220,7 @@ MR_MercuryFileStruct mercury_open(string filename, string openmode,
      if (stream == null) {
          return null;
      } else {
-        // we initialize the `reader' and `writer' fields to null;
+        // We initialize the `reader' and `writer' fields to null;
          // they will be filled in later if they are needed.
          return mercury_file_init(new System.IO.BufferedStream(stream),
              null, null, line_ending);
@@ -7236,6 +7236,17 @@ MR_MercuryFileStruct mercury_open(string filename, string openmode,
  throw_io_error(Message) :-
      throw(io_error(Message)).

+:- pragma foreign_code("Java", "
+
+    public static void throw_io_error(String msg) {
+        if (msg == null) {
+            io.ML_throw_io_error(""null"");
+        } else {
+            io.ML_throw_io_error(msg);
+        }
+    }
+").
+
  :- pragma foreign_code("C", "

  void
@@ -8524,7 +8535,7 @@ flush_binary_output(binary_output_stream(Stream), !IO) :-
      try {
          ((io.MR_BinaryFile) Stream).seek_binary(Flag, Off);
      } catch (java.io.IOException e) {
-        io.ML_throw_io_error(e.getMessage());
+        io.throw_io_error(e.getMessage());
      }
  ").

@@ -9640,7 +9651,7 @@ set_binary_output_stream(binary_output_stream(NewStream),
              Stream = new MR_TextOutputFile(
                  new java.io.FileOutputStream(FileName, true));
          } else {
-            io.ML_throw_io_error(""io.do_open_text: "" +
+            io.throw_io_error(""io.do_open_text: "" +
                  ""Invalid open mode"" + "" \\"""" + Mode + ""\\"""");
              throw new Error(""unreachable"");
          }
@@ -9675,7 +9686,7 @@ set_binary_output_stream(binary_output_stream(NewStream),
                      new java.io.FileOutputStream(FileName, true));
                  break;
              default:
-                io.ML_throw_io_error(""Invalid file opening mode: "" + Mode);
+                io.throw_io_error(""Invalid file opening mode: "" + Mode);
                  Stream = null;
                  break;
          }
@@ -9772,7 +9783,7 @@ close_binary_output(binary_output_stream(Stream), !IO) :-
      try {
          Stream.close();
      } catch (java.io.IOException e) {
-        io.ML_throw_io_error(e.getMessage());
+        io.throw_io_error(e.getMessage());
      }
  ").

@@ -10271,7 +10282,10 @@ command_line_argument(_, "") :-
      } catch (java.lang.Exception e) {
          Status  = 1;
          Success = bool.NO;
-        Msg     = e.getMessage();
+        Msg = e.getMessage();
+        if (Msg == null) {
+            Msg = ""null"";
+        }
      }
  ").

@@ -11136,6 +11150,9 @@ remove_file(FileName, Result, !IO) :-
      } catch (java.lang.Exception e) {
          RetVal = -1;
          RetStr = e.getMessage();
+        if (RetStr == null) {
+            RetStr = ""null"";
+        }
      }
  ").

@@ -11284,6 +11301,9 @@ rename_file(OldFileName, NewFileName, Result, IO0, IO) :-
      } catch (java.lang.Exception e) {
          RetVal = -1;
          RetStr = e.getMessage();
+        if (RetStr == null) {
+            RetStr = ""null"";
+        }
      }
  ").