diff options
Diffstat (limited to 'site/docs/skylark/macros.md')
| -rw-r--r-- | site/docs/skylark/macros.md | 11 |
1 files changed, 10 insertions, 1 deletions
diff --git a/site/docs/skylark/macros.md b/site/docs/skylark/macros.md index 9d32c77bee..0a7458c5ef 100644 --- a/site/docs/skylark/macros.md +++ b/site/docs/skylark/macros.md @@ -63,7 +63,16 @@ optional (don't give a default value). * The `name` attribute of rules generated by a macro should include the name argument as a prefix. For example, `macro(name = "foo")` can generate a - cc_library `foo` and a genrule `foo_gen`. + `cc_library` `foo` and a genrule `foo_gen`. + +* In most cases, optional parameters should have a default value of `None`. + `None` can be passed directly to native rules, which treat it the same as if + you had not passing any argument. Thus, there is no need to replace it with + `0`, `False`, or `[]` for this purpose. Instead, the macro should defer to the + rules it creates, as their defaults may be complex or may change over time. + Additionally, a parameter that is explicitly set to its default value looks + different than one that is never set (or set to `None`) when accessed through + the query language or build-system internals. * Macros should have an optional `visibility` argument. |