fix(format): separate an empty TEXT body from the next block

The one-blank rule before a new block skipped every line that followed a
TEXT directive, not just the function's first label, so a TEXT with an
empty body ran straight into the next declaration.  The exemption now
applies to labels only, and the directive shapes around GLOBL and DATA
ranges are pinned.

Assisted-by: GLM 5.3

format/format_test.go

@@ -285,6 +285,31 @@ func TestFlagListRoundTrip(t *testing.T) {
 	}
 }
 
+// TestDirectiveShapesRoundTrip pins the directive shapes the corpus and the
+// runtime write around GLOBL and DATA: each formats to itself, because the
+// offset, width and flag spellings are load-bearing operand text.  An empty
+// TEXT body followed by another declaration keeps the one-blank rule of any
+// new block, the previous function having no first label to carry it.
+func TestDirectiveShapesRoundTrip(t *testing.T) {
+	for _, in := range []string{
+		"TEXT ·f(SB), NOSPLIT, $0\n",
+		"TEXT ·f(SB), NOSPLIT, $0\n\nTEXT ·g(SB), NOSPLIT, $0\n\tRET\n",
+		"GLOBL divtab<>(SB), RODATA, $64\nDATA divtab<>+0x00(SB)/4, $0xf4f8fcff\nDATA divtab<>+0x04(SB)/4, $0xe6eaedf0\n",
+		"DATA d<>+0(SB)/8, $-1\nDATA d<>+8(SB)/8, $0xFFFFFFFFFFFFFFFF\n\nGLOBL d<>(SB), $16\n",
+		"GLOBL ·x(SB), $8\n",
+		"GLOBL ·x(SB), 8, $8\n",
+		"DATA d<>+0(SB)/4, $1\n\nGLOBL d<>(SB), RODATA, $4\n",
+	} {
+		if got := Source(in); got != in {
+			t.Errorf("formatting %q:\n got %q", in, got)
+			continue
+		}
+		if _, errs := parser.Parse("in.s", in); len(errs) > 0 {
+			t.Errorf("%q does not parse: %v", in, errs)
+		}
+	}
+}
+
 // TestCRLFInputIsNormalisedToLF checks that a CRLF file comes out with
 // uniform LF endings: a // comment must not carry its line's trailing \r
 // into the output.