vendor/github.com/hashicorp/terraform/terraform/graph_walk.go

   1 package terraform
   2
   3 import (
   4         "github.com/hashicorp/terraform/dag"
   5 )
   6
   7 // GraphWalker is an interface that can be implemented that when used
   8 // with Graph.Walk will invoke the given callbacks under certain events.
   9 type GraphWalker interface {
  10         EnterPath([]string) EvalContext
  11         ExitPath([]string)
  12         EnterVertex(dag.Vertex)
  13         ExitVertex(dag.Vertex, error)
  14         EnterEvalTree(dag.Vertex, EvalNode) EvalNode
  15         ExitEvalTree(dag.Vertex, interface{}, error) error
  16 }
  17
  18 // GrpahWalkerPanicwrapper can be optionally implemented to catch panics
  19 // that occur while walking the graph. This is not generally recommended
  20 // since panics should crash Terraform and result in a bug report. However,
  21 // this is particularly useful for situations like the shadow graph where
  22 // you don't ever want to cause a panic.
  23 type GraphWalkerPanicwrapper interface {
  24         GraphWalker
  25
  26         // Panic is called when a panic occurs. This will halt the panic from
  27         // propogating so if the walker wants it to crash still it should panic
  28         // again. This is called from within a defer so runtime/debug.Stack can
  29         // be used to get the stack trace of the panic.
  30         Panic(dag.Vertex, interface{})
  31 }
  32
  33 // GraphWalkerPanicwrap wraps an existing Graphwalker to wrap and swallow
  34 // the panics. This doesn't lose the panics since the panics are still
  35 // returned as errors as part of a graph walk.
  36 func GraphWalkerPanicwrap(w GraphWalker) GraphWalkerPanicwrapper {
  37         return &graphWalkerPanicwrapper{
  38                 GraphWalker: w,
  39         }
  40 }
  41
  42 type graphWalkerPanicwrapper struct {
  43         GraphWalker
  44 }
  45
  46 func (graphWalkerPanicwrapper) Panic(dag.Vertex, interface{}) {}
  47
  48 // NullGraphWalker is a GraphWalker implementation that does nothing.
  49 // This can be embedded within other GraphWalker implementations for easily
  50 // implementing all the required functions.
  51 type NullGraphWalker struct{}
  52
  53 func (NullGraphWalker) EnterPath([]string) EvalContext                  { return new(MockEvalContext) }
  54 func (NullGraphWalker) ExitPath([]string)                               {}
  55 func (NullGraphWalker) EnterVertex(dag.Vertex)                          {}
  56 func (NullGraphWalker) ExitVertex(dag.Vertex, error)                    {}
  57 func (NullGraphWalker) EnterEvalTree(v dag.Vertex, n EvalNode) EvalNode { return n }
  58 func (NullGraphWalker) ExitEvalTree(dag.Vertex, interface{}, error) error {
  59         return nil
  60 }