avoid demo lump name collisions (#712)

* check if the demo file name gets truncated to a lump name that is already present

* only apply to demos loaded from the command line

* no need to copy string, lumpinfo[] isn't going to change anymore at this point

* lumps called DEMO* are considered safe

* correct order

* Update w_wad.c

* comments

* reverse search order

src/g_game.c

@@ -3675,6 +3675,9 @@ void D_CheckNetPlaybackSkip(void);
 
 void G_DeferedPlayDemo(char* name)
 {
+  // [FG] avoid demo lump name collisions
+  W_DemoLumpNameCollision(&name);
+
   defdemoname = name;
   gameaction = ga_playdemo;
 

src/w_wad.c

@@ -555,6 +555,47 @@ boolean W_IsIWADLump (const int lump)
 	       lumpinfo[lump].wad_file == wadfiles[0];
 }
 
+// [FG] avoid demo lump name collisions
+void W_DemoLumpNameCollision(char **name)
+{
+  const char *const safename = "DEMO1";
+  char basename[9];
+  int i, lump;
+
+  ExtractFileBase(*name, basename);
+
+  // [FG] lumps called DEMO* are considered safe
+  if (!strncasecmp(basename, safename, 4))
+  {
+    return;
+  }
+
+  lump = W_CheckNumForName(basename);
+
+  if (lump >= 0)
+  {
+    for (i = lump - 1; i >= 0; i--)
+    {
+      if (!strncasecmp(lumpinfo[i].name, basename, 8))
+      {
+        break;
+      }
+    }
+
+    if (i >= 0)
+    {
+      fprintf(stderr, "Demo lump name collision detected with lump \'%.8s\' from %s.\n",
+              lumpinfo[i].name, W_WadNameForLump(i));
+
+      // [FG] the DEMO1 lump is almost certainly always a demo lump
+      M_StringCopy(lumpinfo[lump].name, safename, 8);
+      *name = lumpinfo[lump].name;
+
+      W_InitLumpHash();
+    }
+  }
+}
+
 void W_CloseFileDescriptors(void)
 {
   int i;

src/w_wad.h

@@ -121,6 +121,7 @@ extern void WritePredefinedLumpWad(const char *filename); // jff 5/6/98
 // [FG] name of the WAD file that contains the lump
 const char *W_WadNameForLump (const int lump);
 boolean W_IsIWADLump (const int lump);
+void W_DemoLumpNameCollision(char **name);
 
 void W_CloseFileDescriptors(void);