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Diffstat (limited to 'site/versions/master/docs/skylark/rules.md')
| -rw-r--r-- | site/versions/master/docs/skylark/rules.md | 28 |
1 files changed, 16 insertions, 12 deletions
diff --git a/site/versions/master/docs/skylark/rules.md b/site/versions/master/docs/skylark/rules.md index 6e8023d2e5..525fe59b26 100644 --- a/site/versions/master/docs/skylark/rules.md +++ b/site/versions/master/docs/skylark/rules.md @@ -329,18 +329,22 @@ use `ctx.host_fragments` instead. ## Providers -Providers are used to access information from other rules. A rule depending on -another rule has access to the data the latter provides. These data can be e.g. -output files, the libraries the dependent rule is using to link or compile, or -anything the depending rule should know about. Using providers is the only way -to exchange data between rules. - -A rule can only access data provided by its direct dependencies, not that of -transitive dependencies: if rule `top` depends on `middle`, and `middle` depends -on `bottom`, then `middle` is a direct dependency of `top` and `bottom` is a -transitive dependency of `top`. In this scenario `top` can only access data -provided by `middle`. If `middle` also provides the data that `bottom` provided -to it, then and only then can `top` access it. +Providers are pieces of information that a rule exposes to other rules that +depend on it. This data can include output files, libraries, parameters to pass +on a tool's command line, or anything else the depending rule should know about. +Providers are the only mechanism to exchange data between rules, and can be +thought of as part of a rule's public interface (loosely analogous to a +function's return value). + +A rule can only see the providers of its direct dependencies. If there is a rule +`top` that depends on `middle`, and `middle` depends on `bottom`, then we say +that `middle` is a direct dependency of `top`, while `bottom` is a transitive +dependency of `top`. In this case, `top` can see the providers of `middle`. The +only way for `top` to see any information from `bottom` is if `middle` +re-exports this information in its own providers; this is how transitive +information can be accumulated from all dependencies. In such cases, consider +using [depsets](depsets.md) to hold the data more efficiently without excessive +copying. The following data types can be passed using providers: |