Also get types from second-level imports

In the added test (from the README), we import "os" and "io/ioutil" but
not "io", where the interface is defined.

Stop at second-level since that should be enough.

Fixes #34.

README.md

@@ -35,7 +35,7 @@ also trigger a warning - if `f` were an `io.ReadCloser`, the same
 message would appear.
 
 It suggests interface types defined both in the func's package and the
-package's imports.
+package's imports (two levels; direct imports and their direct imports).
 
 ### False positives
 

cache.go

@@ -16,10 +16,16 @@ type pkgTypes struct {
 func (p *pkgTypes) getTypes(pkg *types.Package) {
 	p.ifaces = make(map[string]string)
 	p.funcSigns = make(map[string]bool)
-	addTypes := func(impPath string, ifs map[string]string, funs map[string]bool, top bool) {
+	done := make(map[*types.Package]bool)
+	addTypes := func(pkg *types.Package, top bool) {
+		if done[pkg] {
+			return
+		}
+		done[pkg] = true
+		ifs, funs := fromScope(pkg.Scope())
 		fullName := func(name string) string {
 			if !top {
-				return impPath + "." + name
+				return pkg.Path() + "." + name
 			}
 			return name
 		}
@@ -35,9 +41,10 @@ func (p *pkgTypes) getTypes(pkg *types.Package) {
 		}
 	}
 	for _, imp := range pkg.Imports() {
-		ifs, funs := fromScope(imp.Scope())
-		addTypes(imp.Path(), ifs, funs, false)
+		addTypes(imp, false)
+		for _, imp2 := range imp.Imports() {
+			addTypes(imp2, false)
+		}
 	}
-	ifs, funs := fromScope(pkg.Scope())
-	addTypes(pkg.Path(), ifs, funs, true)
+	addTypes(pkg, true)
 }

testdata/files/readme.go

@@ -0,0 +1,16 @@
+package foo
+
+import (
+	"io/ioutil"
+	"os"
+)
+
+func ProcessInput(f *os.File) error { // WARN f can be io.Reader
+	b, err := ioutil.ReadAll(f)
+	if err != nil {
+		return err
+	}
+	return processBytes(b)
+}
+
+func processBytes(b []byte) error { return nil }