pkgset: add transitive reduction

Fixes #39

main.go

@@ -46,7 +46,7 @@ func (*ExprHelp) Usage() string {
 # Basic operations
 	There are a few basic oprations specified for manipulating sets of packages.
 
-	a b c;  
+	a b c;
 	a + b + c;  add(a, b, c);  or(a, b, c)
 		returns packages that are used by a or b
 
@@ -80,6 +80,9 @@ func (*ExprHelp) Usage() string {
 	reach(a, b);
 		lists packages from a that can reach a package in b
 
+	transitive(a);
+		a transitive reduction in package dependencies
+
 # Tags and OS:
 
 	test=1(a);
@@ -94,17 +97,17 @@ func (*ExprHelp) Usage() string {
 # Example expressions
 
 	github.com/loov/goda:deps
-		all dependencies for "github.com/loov/goda" package 
+		all dependencies for "github.com/loov/goda" package
 
 	github.com/loov/goda/...:noroot
-		all dependencies for "github.com/loov/goda" sub-package 
+		all dependencies for "github.com/loov/goda" sub-package
 
 	shared(github.com/loov/goda/pkgset, github.com/loov/goda/templates)
 		packages shared by "github.com/loov/goda/pkgset" and "github.com/loov/goda/templates"
 
 	github.com/loov/goda/...:noroot - golang.org/x/tools/...
 		all dependencies excluding golang.org/x/tools
-	
+
 	reach(github.com/loov/goda/...:root, golang.org/x/tools/go/packages:root)
 		packages in github.com/loov/goda/ that use golang.org/x/tools/go/packages
 `

pkgset/calc.go

@@ -121,6 +121,13 @@ func Calc(parentContext context.Context, expr []string) (Set, error) {
 				args, err := evalArgs(ctx, e.Args)
 				return Reach(args[0], args[1]), err
 
+			case "transitive":
+				if len(e.Args) != 1 {
+					return nil, fmt.Errorf("reach requires one argument: %v", e)
+				}
+				args, err := evalArgs(ctx, e.Args)
+				return Transitive(args[0]), err
+
 			default:
 				return nil, fmt.Errorf("unknown func %v: %v", e.Name, e)
 			}

pkgset/set.go

@@ -90,7 +90,7 @@ func (set Set) IncludeRecursive(p *packages.Package) {
 func (set Set) Clone() Set {
 	r := make(Set, len(set))
 	for pid, p := range set {
-		r[pid] = p
+		r[pid] = p // TODO: make a deep clone
 	}
 	return r
 }
@@ -187,6 +187,34 @@ func Reach(a, b Set) Set {
 	return result
 }
 
+// Transitive returns transitive reduction.
+func Transitive(a Set) Set {
+	result := a.Clone()
+
+	var includeDeps func(p *packages.Package, r map[string]struct{})
+	includeDeps = func(p *packages.Package, r map[string]struct{}) {
+		for _, c := range p.Imports {
+			if _, visited := r[c.ID]; visited {
+				continue
+			}
+			r[c.ID] = struct{}{}
+			includeDeps(c, r)
+		}
+	}
+
+	for _, p := range result {
+		indirectDeps := make(map[string]struct{})
+		for _, c := range p.Imports {
+			includeDeps(c, indirectDeps)
+		}
+		for dep := range indirectDeps {
+			delete(p.Imports, dep)
+		}
+	}
+
+	return result
+}
+
 // Sources returns packages that don't have incoming edges
 func Sources(a Set) Set {
 	incoming := map[string]int{}