emitter - ensure_padding_newlines

Change function to do nothing if called with a empty buffer.
Essentially, padding should only be used as a way of creating
space between two paragraphs/lines.

gcgen/emitter.py

@@ -155,16 +155,22 @@ def lines(self) -> Iterator[str]:
         for elem in self._buf:
             yield str(elem)
 
-    def ensure_newlines(self, n: int):
-        """Ensure (at least) `n` empty lines."""
+    def ensure_padding_lines(self, nlines: int):
+        """Ensure (at least) `n` empty lines of padding between two sections
+
+        NOTE: if the buffer is empty, this call is a NO-OP.
+        """
         # if empty, n newlines suffice
         # if some line BEFORE, then n+1 newlines needed
-        buf_end = self._buf[-(n + 1):]
+        if not self._buf:
+            return
+
+        buf_end = self._buf[-(nlines + 1) :]
         buf_end.reverse()
         num_newlines = 0
         for e in buf_end:
             if e != "\n":
-                n += 1
+                nlines += 1
                 break
             num_newlines += 1
-        self._buf.extend("\n" for _ in range(0, n - num_newlines))
+        self._buf.extend("\n" for _ in range(0, nlines - num_newlines))

tests/test_emitter.py

@@ -108,19 +108,22 @@ def test_dedent_guard():
 
 
 @pytest.mark.parametrize("n", [0, 1, 2, 3, 4])
-def test_newlines(n):
+def test_newlines_empty_is_noop(n):
+    """
+    When calling with an empty buffer, do not add any newlines.
+    """
     e = Emitter("")
     assert e._buf[-n:] == []
-    e.ensure_newlines(n)
-    assert e._buf[-n:] == ["\n" for _ in range(0, n)]
+    e.ensure_padding_lines(n)
+    assert e._buf[-n:] == []
 
 
 @pytest.mark.parametrize("n", [0, 1, 2, 3, 4])
 def test_newlines2(n):
     e = Emitter("")
     assert e._buf[-n:] == []
     e.emitln("hello, world")
-    e.ensure_newlines(n)
+    e.ensure_padding_lines(n)
     # Note that an additional "\n" (newline) entry is tolerated
     # this is the element which terminates the preceding line.
     expected = ["hello, world", "\n"]