listPackages to return a PackageTree

Also add several more tests.

_testdata/src/m1p/a.go

@@ -0,0 +1,12 @@
+package m1p
+
+import (
+	"sort"
+
+	"github.com/sdboyer/vsolver"
+)
+
+var (
+	_ = sort.Strings
+	_ = vsolver.Solve
+)

_testdata/src/m1p/b.go

@@ -0,0 +1,11 @@
+package m1p
+
+import (
+	"os"
+	"sort"
+)
+
+var (
+	_ = sort.Strings
+	_ = os.PathSeparator
+)

_testdata/src/nest/a.go

@@ -0,0 +1,12 @@
+package simple
+
+import (
+	"sort"
+
+	"github.com/sdboyer/vsolver"
+)
+
+var (
+	_ = sort.Strings
+	_ = vsolver.Solve
+)

_testdata/src/nest/m1p/a.go

@@ -0,0 +1,12 @@
+package m1p
+
+import (
+	"sort"
+
+	"github.com/sdboyer/vsolver"
+)
+
+var (
+	_ = sort.Strings
+	_ = vsolver.Solve
+)

_testdata/src/nest/m1p/b.go

@@ -0,0 +1,11 @@
+package m1p
+
+import (
+	"os"
+	"sort"
+)
+
+var (
+	_ = sort.Strings
+	_ = os.PathSeparator
+)

_testdata/src/ren/m1p/a.go

@@ -0,0 +1,12 @@
+package m1p
+
+import (
+	"sort"
+
+	"github.com/sdboyer/vsolver"
+)
+
+var (
+	_ = sort.Strings
+	_ = vsolver.Solve
+)

_testdata/src/ren/m1p/b.go

@@ -0,0 +1,11 @@
+package m1p
+
+import (
+	"os"
+	"sort"
+)
+
+var (
+	_ = sort.Strings
+	_ = os.PathSeparator
+)

_testdata/src/ren/simple/a.go

@@ -0,0 +1,12 @@
+package simple
+
+import (
+	"sort"
+
+	"github.com/sdboyer/vsolver"
+)
+
+var (
+	_ = sort.Strings
+	_ = vsolver.Solve
+)

_testdata/src/simpleallt/t_test.go

@@ -0,0 +1,11 @@
+package simple
+
+import (
+	"math/rand"
+	"strconv"
+)
+
+var (
+	_ = rand.Int()
+	_ = strconv.Unquote
+)

analysis.go

@@ -11,6 +11,13 @@ import (
 	"text/scanner"
 )
 
+type PackageTree map[string]PackageOrErr
+
+type PackageOrErr struct {
+	P   Package
+	Err error
+}
+
 var osList []string
 var archList []string
 var stdlib = make(map[string]struct{})