Fix workingdirinit step for Windows tasks

This change fixes an issue where Windows tasks would fail with an
error:
Failed to mkdir "\\ko-app\\workingdirinit": mkdir \ko-app\workingdirinit:
The system cannot find the path specified.
The workingdirinit step now correctly parses os.Args and appends 'C:'
on Windows if the path is absolute. Unit tests for Windows and Linux
have also been added.

cmd/workingdirinit/main.go

@@ -20,16 +20,37 @@ import (
 	"log"
 	"os"
 	"path/filepath"
+	"runtime"
 	"strings"
 )
 
 func main() {
-	for _, d := range os.Args {
-		p := filepath.Clean(d)
-		if !filepath.IsAbs(p) || strings.HasPrefix(p, "/workspace/") {
+	for i, d := range os.Args {
+		// os.Args[0] is the path to this executable, so we should skip it
+		if i == 0 {
+			continue
+		}
+
+		ws := cleanPath("/workspace/")
+		p := cleanPath(d)
+
+		if !filepath.IsAbs(p) || strings.HasPrefix(p, ws+string(filepath.Separator)) {
 			if err := os.MkdirAll(p, 0755); err != nil {
 				log.Fatalf("Failed to mkdir %q: %v", p, err)
 			}
 		}
 	}
 }
+
+func cleanPath(path string) string {
+	p := filepath.Clean(path)
+
+	if runtime.GOOS == "windows" {
+		// Append 'C:' if the path is absolute (i.e. it begins with a single '\')
+		if strings.HasPrefix(p, "\\") && !strings.HasPrefix(p, "\\\\") {
+			p = "C:" + p
+		}
+	}
+
+	return p
+}

cmd/workingdirinit/main_test.go

@@ -0,0 +1,73 @@
+//go:build linux
+// +build linux
+
+/*
+Copyright 2023 The Tekton Authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+	http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+package main
+
+import (
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+)
+
+type testCase struct {
+	value    string
+	expected string
+}
+
+var testCases []testCase = []testCase{
+	{
+		// Test trailing path separator
+		value:    "/workspace/",
+		expected: "/workspace",
+	},
+	{
+		// Test workspace subdirectory
+		value:    "/workspace/foobar",
+		expected: "/workspace/foobar",
+	},
+	{
+		// Test double path separator
+		value:    "/foo//bar",
+		expected: "/foo/bar",
+	},
+	{
+		// Test relative path with './' prefix
+		value:    "./foo/bar",
+		expected: "foo/bar",
+	},
+	{
+		// Test relative path with no prefix
+		value:    "foo/bar",
+		expected: "foo/bar",
+	},
+	{
+		// Test empty string
+		value:    "",
+		expected: ".",
+	},
+}
+
+func TestCleanPath(t *testing.T) {
+	for _, tc := range testCases {
+		diff := cmp.Diff(tc.expected, cleanPath(tc.value))
+
+		if diff != "" {
+			t.Errorf("diff(-want, +got): %s", diff)
+		}
+	}
+}

cmd/workingdirinit/main_windows_test.go

@@ -0,0 +1,83 @@
+//go:build windows
+// +build windows
+
+/*
+Copyright 2023 The Tekton Authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+	http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+package main
+
+import (
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+)
+
+type testCase struct {
+	value    string
+	expected string
+}
+
+var testCases []testCase = []testCase{
+	{
+		// Test trailing path separator
+		value:    `/workspace/`,
+		expected: `C:\workspace`,
+	},
+	{
+		// Test workspace subdirectory
+		value:    `/workspace/foobar`,
+		expected: `C:\workspace\foobar`,
+	},
+	{
+		// Test double path separator
+		value:    `/foo//bar`,
+		expected: `C:\foo\bar`,
+	},
+	{
+		// Test relative path with './' prefix
+		value:    `./foo/bar`,
+		expected: `foo\bar`,
+	},
+	{
+		// Test relative path with no prefix
+		value:    `foo/bar`,
+		expected: `foo\bar`,
+	},
+	{
+		// Test empty string
+		value:    ``,
+		expected: `.`,
+	},
+	{
+		// Test UNC path
+		value:    `\\foo\bar`,
+		expected: `\\foo\bar`,
+	},
+	{
+		// Test native Windows path format
+		value:    `C:\workspace\foobar`,
+		expected: `C:\workspace\foobar`,
+	},
+}
+
+func TestCleanPath(t *testing.T) {
+	for _, tc := range testCases {
+		diff := cmp.Diff(tc.expected, cleanPath(tc.value))
+
+		if diff != "" {
+			t.Errorf("diff(-want, +got): %s", diff)
+		}
+	}
+}