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After hooking into composer, the transpilation process begins.
All dependencies of a package with a phabel configuration are processed with phabel with the same configuration, to allow transpiling towards an arbitrary version of PHP; composer takes care of choosing the best package, according to the current version of PHP.
All plugins specified in the configuration of each package are added to the phabel plugin graph.
The plugin graph takes care of properly trickling configuration values and plugins down the dependency graph, as well as plugin graph optimization by merging multiple transforms (if allowed) in a single AST traversal.
It will also detect circular references in plugin dependencies.
Each phabel plugin can specify multiple leave* and enter* methods, called when traversing down or up the dependency graph.
These methods will be called only for nodes matching the typehint of the parameter.
A second, optional parameter can be provided, to allow the Traverser to pass a Context object with helper methods for replacing nodes in arbitrary positions of the AST stack.
Plugins can also specify other plugins as "dependencies" or "reverse dependencies", with the previous, next, withPrevious, withNext methods, to force some transforms to run before others.
By using the *with* methods, additional plugin graph optimization is allowed by merging multiple transforms in a single AST traversal.
Each phabel plugin can also accept a configuration: this a simple way to reuse code, by specifying a single plugin for a class of transforms, and then requiring it from other plugins, specifying a specific configuration to trigger only certain transforms.
Configuration arrays are coupled with plugins when resolving the plugin graph.
When possible, the plugin graph will try to merge a plugin with multiple configs into a single (or fewer) plugins using the mergeConfigs method of the plugin.
This merge method will be called automatically during plugin graph flattening, if requirement links allow it.
Multiple transforms are available, covering all PHP 7 features.
More complex and generic transforms like typehint and nested expression polyfilling can be found in the plugin folder.