bitbake: ConfHandler/BBHandler: Improve comment error messages and add tests

Currently if you trigger one of the comment errors, the newline characters
are stripped and the line numbers are incorrect. In one case it prints
the empty line which is also unhelpful.

Rework the code around these errors so the line numbers are correct
and the lines in question are more clearly displayed complete with newlines
so the user can more clearly see the error.

I also added a couple of simplistic test cases to ensure that errors
are raised by the two known comment format errors.

[YOCTO #11904]

(Bitbake rev: 712da71b24445c814d79a206ce26188def8fce0a)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/tests/parse.py

@@ -194,3 +194,26 @@ deltask ${EMPTYVAR}
         self.assertTrue('addtask ignored: " do_patch"' in stdout)
         #self.assertTrue('dependent task do_foo for do_patch does not exist' in stdout)
 
+    broken_multiline_comment = """
+# First line of comment \\
+# Second line of comment \\
+
+"""
+    def test_parse_broken_multiline_comment(self):
+        f = self.parsehelper(self.broken_multiline_comment)
+        with self.assertRaises(bb.BBHandledException):
+            d = bb.parse.handle(f.name, self.d)['']
+
+
+    comment_in_var = """
+VAR = " \\
+    SOMEVAL \\
+#   some comment \\
+    SOMEOTHERVAL \\
+"
+"""
+    def test_parse_comment_in_var(self):
+        f = self.parsehelper(self.comment_in_var)
+        with self.assertRaises(bb.BBHandledException):
+            d = bb.parse.handle(f.name, self.d)['']
+