344 lines
13 KiB
Go
344 lines
13 KiB
Go
package refactoring
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import (
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"fmt"
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"log"
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"github.com/hashicorp/terraform/internal/addrs"
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"github.com/hashicorp/terraform/internal/dag"
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"github.com/hashicorp/terraform/internal/logging"
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"github.com/hashicorp/terraform/internal/states"
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)
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// ApplyMoves modifies in-place the given state object so that any existing
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// objects that are matched by a "from" argument of one of the move statements
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// will be moved to instead appear at the "to" argument of that statement.
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//
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// The result is a map from the unique key of each absolute address that was
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// either the source or destination of a move to a MoveResult describing
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// what happened at that address.
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//
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// ApplyMoves does not have any error situations itself, and will instead just
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// ignore any unresolvable move statements. Validation of a set of moves is
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// a separate concern applied to the configuration, because validity of
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// moves is always dependent only on the configuration, not on the state.
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//
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// ApplyMoves expects exclusive access to the given state while it's running.
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// Don't read or write any part of the state structure until ApplyMoves returns.
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func ApplyMoves(stmts []MoveStatement, state *states.State) MoveResults {
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ret := MoveResults{
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Changes: make(map[addrs.UniqueKey]MoveSuccess),
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Blocked: make(map[addrs.UniqueKey]MoveBlocked),
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}
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if len(stmts) == 0 {
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return ret
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}
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// The methodology here is to construct a small graph of all of the move
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// statements where the edges represent where a particular statement
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// is either chained from or nested inside the effect of another statement.
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// That then means we can traverse the graph in topological sort order
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// to gradually move objects through potentially multiple moves each.
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g := buildMoveStatementGraph(stmts)
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// If the graph is not valid the we will not take any action at all. The
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// separate validation step should detect this and return an error.
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if diags := validateMoveStatementGraph(g); diags.HasErrors() {
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log.Printf("[ERROR] ApplyMoves: %s", diags.ErrWithWarnings())
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return ret
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}
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// The graph must be reduced in order for ReverseDepthFirstWalk to work
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// correctly, since it is built from following edges and can skip over
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// dependencies if there is a direct edge to a transitive dependency.
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g.TransitiveReduction()
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// The starting nodes are the ones that don't depend on any other nodes.
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startNodes := make(dag.Set, len(stmts))
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for _, v := range g.Vertices() {
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if len(g.DownEdges(v)) == 0 {
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startNodes.Add(v)
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}
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}
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if startNodes.Len() == 0 {
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log.Println("[TRACE] refactoring.ApplyMoves: No 'moved' statements to consider in this configuration")
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return ret
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}
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log.Printf("[TRACE] refactoring.ApplyMoves: Processing 'moved' statements in the configuration\n%s", logging.Indent(g.String()))
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recordOldAddr := func(oldAddr, newAddr addrs.AbsResourceInstance) {
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oldAddrKey := oldAddr.UniqueKey()
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newAddrKey := newAddr.UniqueKey()
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if prevMove, exists := ret.Changes[oldAddrKey]; exists {
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// If the old address was _already_ the result of a move then
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// we'll replace that entry so that our results summarize a chain
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// of moves into a single entry.
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delete(ret.Changes, oldAddrKey)
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oldAddr = prevMove.From
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}
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ret.Changes[newAddrKey] = MoveSuccess{
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From: oldAddr,
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To: newAddr,
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}
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}
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recordBlockage := func(newAddr, wantedAddr addrs.AbsMoveable) {
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ret.Blocked[newAddr.UniqueKey()] = MoveBlocked{
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Wanted: wantedAddr,
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Actual: newAddr,
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}
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}
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g.ReverseDepthFirstWalk(startNodes, func(v dag.Vertex, depth int) error {
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stmt := v.(*MoveStatement)
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for _, ms := range state.Modules {
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modAddr := ms.Addr
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// We don't yet know that the current module is relevant, and
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// we determine that differently for each the object kind.
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switch kind := stmt.ObjectKind(); kind {
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case addrs.MoveEndpointModule:
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// For a module endpoint we just try the module address
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// directly, and execute the moves if it matches.
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if newAddr, matches := modAddr.MoveDestination(stmt.From, stmt.To); matches {
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log.Printf("[TRACE] refactoring.ApplyMoves: %s has moved to %s", modAddr, newAddr)
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// If we already have a module at the new address then
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// we'll skip this move and let the existing object take
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// priority.
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if ms := state.Module(newAddr); ms != nil {
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log.Printf("[WARN] Skipped moving %s to %s, because there's already another module instance at the destination", modAddr, newAddr)
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recordBlockage(modAddr, newAddr)
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continue
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}
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// We need to visit all of the resource instances in the
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// module and record them individually as results.
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for _, rs := range ms.Resources {
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relAddr := rs.Addr.Resource
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for key := range rs.Instances {
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oldInst := relAddr.Instance(key).Absolute(modAddr)
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newInst := relAddr.Instance(key).Absolute(newAddr)
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recordOldAddr(oldInst, newInst)
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}
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}
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state.MoveModuleInstance(modAddr, newAddr)
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continue
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}
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case addrs.MoveEndpointResource:
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// For a resource endpoint we require an exact containing
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// module match, because by definition a matching resource
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// cannot be nested any deeper than that.
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if !stmt.From.SelectsModule(modAddr) {
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continue
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}
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// We then need to search each of the resources and resource
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// instances in the module.
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for _, rs := range ms.Resources {
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rAddr := rs.Addr
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if newAddr, matches := rAddr.MoveDestination(stmt.From, stmt.To); matches {
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log.Printf("[TRACE] refactoring.ApplyMoves: resource %s has moved to %s", rAddr, newAddr)
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// If we already have a resource at the new address then
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// we'll skip this move and let the existing object take
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// priority.
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if rs := state.Resource(newAddr); rs != nil {
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log.Printf("[WARN] Skipped moving %s to %s, because there's already another resource at the destination", rAddr, newAddr)
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recordBlockage(rAddr, newAddr)
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continue
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}
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for key := range rs.Instances {
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oldInst := rAddr.Instance(key)
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newInst := newAddr.Instance(key)
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recordOldAddr(oldInst, newInst)
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}
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state.MoveAbsResource(rAddr, newAddr)
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continue
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}
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for key := range rs.Instances {
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iAddr := rAddr.Instance(key)
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if newAddr, matches := iAddr.MoveDestination(stmt.From, stmt.To); matches {
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log.Printf("[TRACE] refactoring.ApplyMoves: resource instance %s has moved to %s", iAddr, newAddr)
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// If we already have a resource instance at the new
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// address then we'll skip this move and let the existing
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// object take priority.
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if is := state.ResourceInstance(newAddr); is != nil {
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log.Printf("[WARN] Skipped moving %s to %s, because there's already another resource instance at the destination", iAddr, newAddr)
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recordBlockage(iAddr, newAddr)
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continue
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}
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recordOldAddr(iAddr, newAddr)
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state.MoveAbsResourceInstance(iAddr, newAddr)
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continue
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}
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}
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}
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default:
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panic(fmt.Sprintf("unhandled move object kind %s", kind))
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}
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}
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return nil
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})
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return ret
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}
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// buildMoveStatementGraph constructs a dependency graph of the given move
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// statements, where the nodes are all pointers to statements in the given
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// slice and the edges represent either chaining or nesting relationships.
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//
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// buildMoveStatementGraph doesn't do any validation of the graph, so it
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// may contain cycles and other sorts of invalidity.
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func buildMoveStatementGraph(stmts []MoveStatement) *dag.AcyclicGraph {
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g := &dag.AcyclicGraph{}
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for i := range stmts {
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// The graph nodes are pointers to the actual statements directly.
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g.Add(&stmts[i])
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}
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// Now we'll add the edges representing chaining and nesting relationships.
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// We assume that a reasonable configuration will have at most tens of
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// move statements and thus this N*M algorithm is acceptable.
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for dependerI := range stmts {
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depender := &stmts[dependerI]
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for dependeeI := range stmts {
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if dependerI == dependeeI {
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// skip comparing the statement to itself
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continue
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}
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dependee := &stmts[dependeeI]
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if statementDependsOn(depender, dependee) {
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g.Connect(dag.BasicEdge(depender, dependee))
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}
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}
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}
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return g
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}
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// statementDependsOn returns true if statement a depends on statement b;
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// i.e. statement b must be executed before statement a.
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func statementDependsOn(a, b *MoveStatement) bool {
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// chain-able moves are simple, as on the destination of one move could be
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// equal to the source of another.
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if a.From.CanChainFrom(b.To) {
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return true
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}
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// Statement nesting in more complex, as we have 8 possible combinations to
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// assess. Here we list all combinations, along with the statement which
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// must be executed first when one address is nested within another.
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// A.From IsNestedWithin B.From => A
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// A.From IsNestedWithin B.To => B
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// A.To IsNestedWithin B.From => A
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// A.To IsNestedWithin B.To => B
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// B.From IsNestedWithin A.From => B
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// B.From IsNestedWithin A.To => A
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// B.To IsNestedWithin A.From => B
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// B.To IsNestedWithin A.To => A
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//
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// Since we are only interested in checking if A depends on B, we only need
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// to check the 4 possibilities above which result in B being executed
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// first. If we're there's no dependency at all we can return immediately.
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if !(a.From.NestedWithin(b.To) || a.To.NestedWithin(b.To) ||
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b.From.NestedWithin(a.From) || b.To.NestedWithin(a.From)) {
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return false
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}
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// If a nested move has a dependency, we need to rule out the possibility
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// that this is a move inside a module only changing indexes. If an
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// ancestor module is only changing the index of a nested module, any
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// nested move statements are going to match both the From and To address
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// when the base name is not changing, causing a cycle in the order of
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// operations.
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// if A is not declared in an ancestor module, then we can't be nested
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// within a module index change.
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if len(a.To.Module()) >= len(b.To.Module()) {
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return true
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}
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// We only want the nested move statement to depend on the outer module
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// move, so we only test this in the reverse direction.
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if a.From.IsModuleReIndex(a.To) {
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return false
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}
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return true
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}
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// MoveResults describes the outcome of an ApplyMoves call.
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type MoveResults struct {
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// Changes is a map from the unique keys of the final new resource
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// instance addresses to an object describing what changed.
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//
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// This includes one entry for each resource instance address that was
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// the destination of a move statement. It doesn't include resource
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// instances that were not affected by moves at all, but it does include
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// resource instance addresses that were "blocked" (also recorded in
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// BlockedAddrs) if and only if they were able to move at least
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// partially along a chain before being blocked.
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//
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// In the return value from ApplyMoves, all of the keys are guaranteed to
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// be unique keys derived from addrs.AbsResourceInstance values.
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Changes map[addrs.UniqueKey]MoveSuccess
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// Blocked is a map from the unique keys of the final new
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// resource instances addresses to information about where they "wanted"
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// to move, but were blocked by a pre-existing object at the same address.
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//
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// "Blocking" can arise in unusual situations where multiple points along
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// a move chain were already bound to objects, and thus only one of them
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// can actually adopt the final position in the chain. It can also
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// occur in other similar situations, such as if a configuration contains
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// a move of an entire module and a move of an individual resource into
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// that module, such that the individual resource would collide with a
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// resource in the whole module that was moved.
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//
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// In the return value from ApplyMoves, all of the keys are guaranteed to
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// be unique keys derived from values of addrs.AbsMoveable types.
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Blocked map[addrs.UniqueKey]MoveBlocked
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}
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type MoveSuccess struct {
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From addrs.AbsResourceInstance
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To addrs.AbsResourceInstance
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}
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type MoveBlocked struct {
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Wanted addrs.AbsMoveable
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Actual addrs.AbsMoveable
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}
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// AddrMoved returns true if and only if the given resource instance moved to
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// a new address in the ApplyMoves call that the receiver is describing.
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//
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// If AddrMoved returns true, you can pass the same address to method OldAddr
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// to find its original address prior to moving.
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func (rs MoveResults) AddrMoved(newAddr addrs.AbsResourceInstance) bool {
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_, ok := rs.Changes[newAddr.UniqueKey()]
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return ok
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}
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// OldAddr returns the old address of the given resource instance address, or
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// just returns back the same address if the given instance wasn't affected by
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// any move statements.
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func (rs MoveResults) OldAddr(newAddr addrs.AbsResourceInstance) addrs.AbsResourceInstance {
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change, ok := rs.Changes[newAddr.UniqueKey()]
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if !ok {
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return newAddr
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}
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return change.From
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}
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