Adapt the NUL cell and long line reads to PDCurses

PDCursesMod's setcchar() reads uninitialized memory for an empty string
(PDCursesMod issue #388), so build a cell without text directly.  Its
winnstr() reads at most 512 bytes, and a NUL is written in its ^@ form.

Author: serhiy-storchaka

Lib/test/test_curses.py

@@ -1176,7 +1176,11 @@ def test_cell_null_char(self):
         # A cell holding a NUL reads back as the cell that writes it.
         win = curses.newwin(3, 8, 0, 0)
         win.insch(0, 0, '\0')
-        self.assertEqual(win.in_wch(0, 0), cell)
+        if is_pdcurses:
+            # PDCurses writes a NUL as "^@".
+            self.assertEqual(str(win.in_wch(0, 0)), '^')
+        else:
+            self.assertEqual(win.in_wch(0, 0), cell)
         # A string of cells cannot hold a NUL: it would end a batch write.
         self.assertRaises(ValueError, curses.complexstr, 'a\0b')
         self.assertRaises(ValueError, curses.complexstr, '\0')
@@ -1293,7 +1297,9 @@ def test_read_long_line(self):
             with self.subTest(ch=ch):
                 line = ch * (width - 1) + ' '   # the last cell is left blank
                 pad.addstr(0, 0, line[:-1])
-                self.assertEqual(pad.instr(0, 0), line.encode(pad.encoding))
+                if not is_pdcurses:
+                    # PDCurses reads at most 512 bytes.
+                    self.assertEqual(pad.instr(0, 0), line.encode(pad.encoding))
                 self.assertEqual(pad.in_wstr(0, 0), line)
                 self.assertEqual(str(pad.in_wchstr(0, 0)), line)
 

Modules/_cursesmodule.c

@@ -832,18 +832,28 @@ typedef struct {
 static int
 curses_setcchar(cchar_t *wcval, const wchar_t *wstr, attr_t attrs, int pair)
 {
+#if !_NCURSES_EXTENDED_COLOR_FUNCS
+    if (pair > SHRT_MAX) {
+        PyErr_Format(PyExc_OverflowError,
+                     "color pair %d does not fit in a short", pair);
+        return ERR;
+    }
+#endif
+#ifdef PDCURSES
+    /* PDCursesMod's setcchar() does not handle an empty string
+       (PDCursesMod issue #388). */
+    if (wstr[0] == L'\0') {
+        *wcval = (cchar_t)attrs | COLOR_PAIR(pair);
+        return OK;
+    }
+#endif
 #if _NCURSES_EXTENDED_COLOR_FUNCS
     /* The pair passed through the opts slot is authoritative and may exceed
        a short; ncurses then ignores the short argument, but clamp it into
        range so the int-to-short narrowing stays well-defined. */
     short spair = pair <= SHRT_MAX ? (short)pair : SHRT_MAX;
     return setcchar(wcval, wstr, attrs, spair, &pair);
 #else
-    if (pair > SHRT_MAX) {
-        PyErr_Format(PyExc_OverflowError,
-                     "color pair %d does not fit in a short", pair);
-        return ERR;
-    }
     return setcchar(wcval, wstr, attrs, (short)pair, NULL);
 #endif
 }