terraform/terraform/graph_walk.go

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package terraform
import (
"github.com/hashicorp/terraform/dag"
)
// GraphWalker is an interface that can be implemented that when used
// with Graph.Walk will invoke the given callbacks under certain events.
type GraphWalker interface {
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EnterPath([]string) EvalContext
ExitPath([]string)
EnterVertex(dag.Vertex)
ExitVertex(dag.Vertex, error)
EnterEvalTree(dag.Vertex, EvalNode) EvalNode
ExitEvalTree(dag.Vertex, interface{}, error) error
}
// GrpahWalkerPanicwrapper can be optionally implemented to catch panics
// that occur while walking the graph. This is not generally recommended
// since panics should crash Terraform and result in a bug report. However,
// this is particularly useful for situations like the shadow graph where
// you don't ever want to cause a panic.
type GraphWalkerPanicwrapper interface {
GraphWalker
// Panic is called when a panic occurs. This will halt the panic from
// propogating so if the walker wants it to crash still it should panic
// again. This is called from within a defer so runtime/debug.Stack can
// be used to get the stack trace of the panic.
Panic(dag.Vertex, interface{})
}
// GraphWalkerPanicwrap wraps an existing Graphwalker to wrap and swallow
// the panics. This doesn't lose the panics since the panics are still
// returned as errors as part of a graph walk.
func GraphWalkerPanicwrap(w GraphWalker) GraphWalkerPanicwrapper {
return &graphWalkerPanicwrapper{
GraphWalker: w,
}
}
type graphWalkerPanicwrapper struct {
GraphWalker
}
func (graphWalkerPanicwrapper) Panic(dag.Vertex, interface{}) {}
// NullGraphWalker is a GraphWalker implementation that does nothing.
// This can be embedded within other GraphWalker implementations for easily
// implementing all the required functions.
type NullGraphWalker struct{}
func (NullGraphWalker) EnterPath([]string) EvalContext { return new(MockEvalContext) }
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func (NullGraphWalker) ExitPath([]string) {}
func (NullGraphWalker) EnterVertex(dag.Vertex) {}
func (NullGraphWalker) ExitVertex(dag.Vertex, error) {}
func (NullGraphWalker) EnterEvalTree(v dag.Vertex, n EvalNode) EvalNode { return n }
func (NullGraphWalker) ExitEvalTree(dag.Vertex, interface{}, error) error {
return nil
}