filepath: Add a stand-alone package for explicit-OS path logic

Makefile

@@ -53,6 +53,6 @@ test: .gofmt .govet .golint .gotest
 .golint:
 	golint -set_exit_status $(PACKAGES)
 
-UTDIRS = ./validate/...
+UTDIRS = ./filepath/... ./validate/...
 .gotest:
 	go test $(UTDIRS)

filepath/abs.go

@@ -0,0 +1,52 @@
+package filepath
+
+import (
+	"errors"
+	"regexp"
+	"strings"
+)
+
+var windowsAbs = regexp.MustCompile(`^[a-zA-Z]:\\.*$`)
+
+// Abs is a version of path/filepath's Abs with an explicit operating
+// system and current working directory.
+func Abs(os, path, cwd string) (_ string, err error) {
+	if os == "windows" {
+		return "", errors.New("Abs() does not support windows yet")
+	}
+	if IsAbs(os, path) {
+		return Clean(os, path), nil
+	}
+	return Clean(os, Join(os, cwd, path)), nil
+}
+
+// IsAbs is a version of path/filepath's IsAbs with an explicit
+// operating system.
+func IsAbs(os, path string) bool {
+	if os == "windows" {
+		// FIXME: copy hideous logic from Go's
+		// src/path/filepath/path_windows.go into somewhere where we can
+		// put 3-clause BSD licensed code.
+		return windowsAbs.MatchString(path)
+	}
+	sep := Separator(os)
+
+	// POSIX has [1]:
+	//
+	// > If a pathname begins with two successive <slash> characters,
+	// > the first component following the leading <slash> characters
+	// > may be interpreted in an implementation-defined manner,
+	// > although more than two leading <slash> characters shall be
+	// > treated as a single <slash> character.
+	//
+	// And Boost treats // as non-absolute [2], but Linux [3,4], Python
+	// [5] and Go [6] all treat // as absolute.
+	//
+	// [1]: http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13
+	// [2]: https://github.com/boostorg/filesystem/blob/boost-1.64.0/test/path_test.cpp#L861
+	// [3]: http://man7.org/linux/man-pages/man7/path_resolution.7.html
+	// [4]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/filesystems/path-lookup.md?h=v4.12#n41
+	// [5]: https://github.com/python/cpython/blob/v3.6.1/Lib/posixpath.py#L64-L66
+	// [6]: https://go.googlesource.com/go/+/go1.8.3/src/path/path.go#199
+	return strings.HasPrefix(path, string(sep))
+}

filepath/abs_test.go

@@ -0,0 +1,171 @@
+package filepath
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestAbs(t *testing.T) {
+	for _, test := range []struct {
+		os       string
+		path     string
+		cwd      string
+		expected string
+	}{
+		{
+			os:       "linux",
+			path:     "/",
+			cwd:      "/cwd",
+			expected: "/",
+		},
+		{
+			os:       "linux",
+			path:     "/a",
+			cwd:      "/cwd",
+			expected: "/a",
+		},
+		{
+			os:       "linux",
+			path:     "/a/",
+			cwd:      "/cwd",
+			expected: "/a",
+		},
+		{
+			os:       "linux",
+			path:     "//a",
+			cwd:      "/cwd",
+			expected: "/a",
+		},
+		{
+			os:       "linux",
+			path:     ".",
+			cwd:      "/cwd",
+			expected: "/cwd",
+		},
+		{
+			os:       "linux",
+			path:     "./c",
+			cwd:      "/a/b",
+			expected: "/a/b/c",
+		},
+		{
+			os:       "linux",
+			path:     ".//c",
+			cwd:      "/a/b",
+			expected: "/a/b/c",
+		},
+		{
+			os:       "linux",
+			path:     "../a",
+			cwd:      "/cwd",
+			expected: "/a",
+		},
+		{
+			os:       "linux",
+			path:     "../../b",
+			cwd:      "/cwd",
+			expected: "/b",
+		},
+	} {
+		t.Run(
+			fmt.Sprintf("Abs(%q,%q,%q)", test.os, test.path, test.cwd),
+			func(t *testing.T) {
+				abs, err := Abs(test.os, test.path, test.cwd)
+				if err != nil {
+					t.Error(err)
+				} else if abs != test.expected {
+					t.Errorf("unexpected result: %q (expected %q)\n", abs, test.expected)
+				}
+			},
+		)
+	}
+}
+
+func TestIsAbs(t *testing.T) {
+	for _, test := range []struct {
+		os       string
+		path     string
+		expected bool
+	}{
+		{
+			os:       "linux",
+			path:     "/",
+			expected: true,
+		},
+		{
+			os:       "linux",
+			path:     "/a",
+			expected: true,
+		},
+		{
+			os:       "linux",
+			path:     "//",
+			expected: true,
+		},
+		{
+			os:       "linux",
+			path:     "//a",
+			expected: true,
+		},
+		{
+			os:       "linux",
+			path:     ".",
+			expected: false,
+		},
+		{
+			os:       "linux",
+			path:     "./a",
+			expected: false,
+		},
+		{
+			os:       "linux",
+			path:     ".//a",
+			expected: false,
+		},
+		{
+			os:       "linux",
+			path:     "../a",
+			expected: false,
+		},
+		{
+			os:       "linux",
+			path:     "../../a",
+			expected: false,
+		},
+		{
+			os:       "windows",
+			path:     "c:\\",
+			expected: true,
+		},
+		{
+			os:       "windows",
+			path:     "c:\\a",
+			expected: true,
+		},
+		{
+			os:       "windows",
+			path:     ".",
+			expected: false,
+		},
+		{
+			os:       "windows",
+			path:     ".\\a",
+			expected: false,
+		},
+		{
+			os:       "windows",
+			path:     "..\\a",
+			expected: false,
+		},
+	} {
+		t.Run(
+			fmt.Sprintf("IsAbs(%q,%q)", test.os, test.path),
+			func(t *testing.T) {
+				abs := IsAbs(test.os, test.path)
+				if abs != test.expected {
+					t.Errorf("unexpected result: %t (expected %t)\n", abs, test.expected)
+				}
+			},
+		)
+	}
+}

filepath/ancestor.go

@@ -0,0 +1,32 @@
+package filepath
+
+import (
+	"fmt"
+	"strings"
+)
+
+// IsAncestor returns true when pathB is an strict ancestor of pathA,
+// and false where the paths are equal or pathB is outside of pathA.
+// Paths that are not absolute will be made absolute with Abs.
+func IsAncestor(os, pathA, pathB, cwd string) (_ bool, err error) {
+	if pathA == pathB {
+		return false, nil
+	}
+
+	pathA, err = Abs(os, pathA, cwd)
+	if err != nil {
+		return false, err
+	}
+	pathB, err = Abs(os, pathB, cwd)
+	if err != nil {
+		return false, err
+	}
+	sep := Separator(os)
+	if !strings.HasSuffix(pathA, string(sep)) {
+		pathA = fmt.Sprintf("%s%c", pathA, sep)
+	}
+	if pathA == pathB {
+		return false, nil
+	}
+	return strings.HasPrefix(pathB, pathA), nil
+}

filepath/ancestor_test.go

@@ -0,0 +1,113 @@
+package filepath
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestIsAncestor(t *testing.T) {
+	for _, test := range []struct {
+		os       string
+		pathA    string
+		pathB    string
+		cwd      string
+		expected bool
+	}{
+		{
+			os:       "linux",
+			pathA:    "/",
+			pathB:    "/a",
+			cwd:      "/cwd",
+			expected: true,
+		},
+		{
+			os:       "linux",
+			pathA:    "/a",
+			pathB:    "/a",
+			cwd:      "/cwd",
+			expected: false,
+		},
+		{
+			os:       "linux",
+			pathA:    "/a",
+			pathB:    "/",
+			cwd:      "/cwd",
+			expected: false,
+		},
+		{
+			os:       "linux",
+			pathA:    "/a",
+			pathB:    "/ab",
+			cwd:      "/cwd",
+			expected: false,
+		},
+		{
+			os:       "linux",
+			pathA:    "/a/",
+			pathB:    "/a",
+			cwd:      "/cwd",
+			expected: false,
+		},
+		{
+			os:       "linux",
+			pathA:    "//a",
+			pathB:    "/a",
+			cwd:      "/cwd",
+			expected: false,
+		},
+		{
+			os:       "linux",
+			pathA:    "//a",
+			pathB:    "/a/b",
+			cwd:      "/cwd",
+			expected: true,
+		},
+		{
+			os:       "linux",
+			pathA:    "/a",
+			pathB:    "/a/",
+			cwd:      "/cwd",
+			expected: false,
+		},
+		{
+			os:       "linux",
+			pathA:    "/a",
+			pathB:    ".",
+			cwd:      "/cwd",
+			expected: false,
+		},
+		{
+			os:       "linux",
+			pathA:    "/a",
+			pathB:    "b",
+			cwd:      "/a",
+			expected: true,
+		},
+		{
+			os:       "linux",
+			pathA:    "/a",
+			pathB:    "../a",
+			cwd:      "/cwd",
+			expected: false,
+		},
+		{
+			os:       "linux",
+			pathA:    "/a",
+			pathB:    "../a/b",
+			cwd:      "/cwd",
+			expected: true,
+		},
+	} {
+		t.Run(
+			fmt.Sprintf("IsAncestor(%q,%q,%q,%q)", test.os, test.pathA, test.pathB, test.cwd),
+			func(t *testing.T) {
+				ancestor, err := IsAncestor(test.os, test.pathA, test.pathB, test.cwd)
+				if err != nil {
+					t.Error(err)
+				} else if ancestor != test.expected {
+					t.Errorf("unexpected result: %t", ancestor)
+				}
+			},
+		)
+	}
+}