Add tests and docs

logger/doc.go

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+// Package logger provides a global logger interface for logging from plugins.
+//
+// This package is a wrapper for hclog, and it initializes the global logger on import.
+// You can freely write logs from anywhere via the public API according to the log level.
+// The log by hclog is interpreted as a structured log by go-plugin, and the log level
+// can be handled correctly.
+package logger

plugin/fromproto/doc.go

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+// Package fromproto contains an implementation to decode a structure
+// generated from *.proto into a real Go structure. This package is not
+// intended to be used directly from plugins.
+//
+// Many primitives can be handled as-is, but some interfaces and errors
+// require special decoding. The `hcl.Expression` restores the interface
+// by reparsed based on the bytes and their range. The `tflint.Rule`
+// restores the interface by filling the value in a pseudo-structure that
+// satisfies the interface. Error makes use of gRPC error details to recover
+// the wrapped error. Rewrap the error based on the error code obtained
+// from details.
+package fromproto

plugin/host2plugin/doc.go

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+// Package host2plugin contains a gRPC server (plugin) and client (host).
+//
+// In the plugin system, this communication is the first thing that happens,
+// and a plugin must use this package to provide a gRPC server.
+// However, the detailed implementation is hidden in the tflint.RuleSet interface,
+// and plugin developers usually don't need to be aware of gRPC server behavior.
+//
+// When the host initializes a gRPC client, go-plugin starts a gRPC server
+// on the plugin side as another process. This package acts as a wrapper for go-plugin.
+// Separately, the Check function initializes a new gRPC client for plugin-to-host
+// communication. See the plugin2host package for details.
+package host2plugin

plugin/interceptor/doc.go

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+// Package interceptor contains gRPC interceptors.
+// This package is not intended to be used directly from plugins.
+// Its main use today is to insert shared processes such as logging.
+package interceptor

plugin/plugin2host/doc.go

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+// Package plugin2host contains a gRPC server (host) and client (plugin).
+//
+// Communication from the plugin to the host is the second one that occurs.
+// To understand what happens first, see the host2plugin package first.
+// The gRPC client used by the plugin is implicitly initialized by the host2plugin
+// package and hidden in the tflint.Runner interface. Normally, plugin developers
+// do not need to be aware of the details of this client.
+//
+// The host starts a gRPC server as goroutine to respond from the plugin side
+// when calling Check function in host2plugin. Please note that the gRPC server
+// and client startup in plugin2host is not due to go-plugin.
+package plugin2host