tools/loggraphdiff: a simple tool for graph change debugging

tools/loggraphdiff/loggraphdiff.go

@@ -0,0 +1,153 @@
+// loggraphdiff is a tool for interpreting changes to the Terraform graph
+// based on the simple graph printing format used in the TF_LOG=trace log
+// output from Terraform, which looks like this:
+//
+//     aws_instance.b (destroy) - *terraform.NodeDestroyResourceInstance
+//     aws_instance.b (prepare state) - *terraform.NodeApplyableResource
+//       provider.aws - *terraform.NodeApplyableProvider
+//     aws_instance.b (prepare state) - *terraform.NodeApplyableResource
+//       provider.aws - *terraform.NodeApplyableProvider
+//     module.child.aws_instance.a (destroy) - *terraform.NodeDestroyResourceInstance
+//       module.child.aws_instance.a (prepare state) - *terraform.NodeApplyableResource
+//       module.child.output.a_output - *terraform.NodeApplyableOutput
+//       provider.aws - *terraform.NodeApplyableProvider
+//     module.child.aws_instance.a (prepare state) - *terraform.NodeApplyableResource
+//       provider.aws - *terraform.NodeApplyableProvider
+//     module.child.output.a_output - *terraform.NodeApplyableOutput
+//       module.child.aws_instance.a (prepare state) - *terraform.NodeApplyableResource
+//     provider.aws - *terraform.NodeApplyableProvider
+//
+// It takes the names of two files containing this style of output and
+// produces a single graph description in graphviz format that shows the
+// differences between the two graphs: nodes and edges which are only in the
+// first graph are shown in red, while those only in the second graph are
+// shown in green. This color combination is not useful for those who are
+// red/green color blind, so the result can be adjusted by replacing the
+// keywords "red" and "green" with a combination that the user is able to
+// distinguish.
+
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"log"
+	"os"
+	"sort"
+	"strings"
+)
+
+type Graph struct {
+	nodes map[string]struct{}
+	edges map[[2]string]struct{}
+}
+
+func main() {
+	if len(os.Args) != 3 {
+		log.Fatal("usage: loggraphdiff <old-graph-file> <new-graph-file>")
+	}
+
+	old, err := readGraph(os.Args[1])
+	if err != nil {
+		log.Fatal("failed to read %s: %s", os.Args[1], err)
+	}
+	new, err := readGraph(os.Args[2])
+	if err != nil {
+		log.Fatal("failed to read %s: %s", os.Args[1], err)
+	}
+
+	var nodes []string
+	for n := range old.nodes {
+		nodes = append(nodes, n)
+	}
+	for n := range new.nodes {
+		if _, exists := old.nodes[n]; !exists {
+			nodes = append(nodes, n)
+		}
+	}
+	sort.Strings(nodes)
+
+	var edges [][2]string
+	for e := range old.edges {
+		edges = append(edges, e)
+	}
+	for e := range new.edges {
+		if _, exists := old.edges[e]; !exists {
+			edges = append(edges, e)
+		}
+	}
+	sort.Slice(edges, func(i, j int) bool {
+		if edges[i][0] != edges[j][0] {
+			return edges[i][0] < edges[j][0]
+		}
+		return edges[i][1] < edges[j][1]
+	})
+
+	fmt.Println("digraph G {")
+	fmt.Println("  rankdir = \"BT\";\n")
+	for _, n := range nodes {
+		var attrs string
+		_, inOld := old.nodes[n]
+		_, inNew := new.nodes[n]
+		switch {
+		case inOld && inNew:
+			// no attrs required
+		case inOld:
+			attrs = " [color=red]"
+		case inNew:
+			attrs = " [color=green]"
+		}
+		fmt.Printf("    %q%s;\n", n, attrs)
+	}
+	fmt.Println("")
+	for _, e := range edges {
+		var attrs string
+		_, inOld := old.edges[e]
+		_, inNew := new.edges[e]
+		switch {
+		case inOld && inNew:
+			// no attrs required
+		case inOld:
+			attrs = " [color=red]"
+		case inNew:
+			attrs = " [color=green]"
+		}
+		fmt.Printf("    %q -> %q%s;\n", e[0], e[1], attrs)
+	}
+	fmt.Println("}")
+}
+
+func readGraph(fn string) (Graph, error) {
+	ret := Graph{
+		nodes: map[string]struct{}{},
+		edges: map[[2]string]struct{}{},
+	}
+	r, err := os.Open(fn)
+	if err != nil {
+		return ret, err
+	}
+
+	sc := bufio.NewScanner(r)
+	var latestNode string
+	for sc.Scan() {
+		l := sc.Text()
+		dash := strings.Index(l, " - ")
+		if dash == -1 {
+			// invalid line, so we'll ignore it
+			continue
+		}
+		name := l[:dash]
+		if strings.HasPrefix(name, "  ") {
+			// It's an edge
+			name = name[2:]
+			edge := [2]string{latestNode, name}
+			ret.edges[edge] = struct{}{}
+		} else {
+			// It's a node
+			latestNode = name
+			ret.nodes[name] = struct{}{}
+		}
+	}
+
+	return ret, nil
+}