estimate: fix occasional infinite recursion

The "go mod graph" command returns a DAG so there can be no cycles, but
modules can appear multiple times with different versions. When
stripping the version from the modules we can accidentaly introduce
cycles in the DAG by merging multiple versions of a module.

To prevent this, we go back to saving the exact output of "go mod graph"
in memory, including the version strings, and get rid of them when
visiting each node.

Closes: #292

Author: n-peugnet

estimate.go

@@ -277,27 +277,25 @@ func estimate(importpath, revision string) error {
 		// imported it, separated by a single space. The module names
 		// can have a version information delimited by the @ character
 		src, dep, _ := strings.Cut(line, " ")
-		// Get the module names without their version, as we do not use
-		// this information.
 		// The root module is the only one that does not have a version
 		// indication with @ in the output of go mod graph. We use this
 		// to filter out the depencencies of the "dummymod" module.
-		dep, _, _ = strings.Cut(dep, "@")
-		src, _, found := strings.Cut(src, "@")
-		if !found {
+		if !strings.Contains(src, "@") {
 			continue
 		}
 		// Due to importing all packages of the estimated module in a
 		// dummy one, some modules can depend on submodules of the
 		// estimated one. We do as if they are dependencies of the
 		// root one.
-		if strings.HasPrefix(src, importpath+"/") {
+		pattern := fmt.Sprintf("^%s[@/]", regexp.QuoteMeta(importpath))
+		if matched, _ := regexp.MatchString(pattern, src); matched {
 			src = importpath
 		}
 		// go mod graph also lists indirect dependencies as dependencies
 		// of the current module, so we filter them out. They will still
 		// appear later.
-		if src == importpath && !directDeps[dep] {
+		depMod, _, _ := strings.Cut(dep, "@")
+		if src == importpath && !directDeps[depMod] {
 			continue
 		}
 		depNode, ok := nodes[dep]
@@ -320,7 +318,10 @@ func estimate(importpath, revision string) error {
 	needed := make(map[string]int)
 	var visit func(n *Node, indent int)
 	visit = func(n *Node, indent int) {
-		mod := n.name
+		// Get the module name without its version, as go mod graph
+		// can return multiple times the same module with different
+		// versions.
+		mod, _, _ := strings.Cut(n.name, "@")
 		count, isNeeded := needed[mod]
 		if isNeeded {
 			count++