fix: corrects handling of UNC root paths in windows.

---------
Signed-off-by: Luis M. Santos <luis.santos2@nih.gov>
Co-authored-by: Luis M. Santos <luis.santos2@nih.gov>

syft/internal/windows/path.go

@@ -8,6 +8,10 @@ import (
 )
 
 const windowsGoOS = "windows"
+const windowsUNCPathPrefix = "\\\\"
+const windowsDriveColon = ":"
+const windowsDrivePathTerminator = ":\\"
+const windowsUNCPathTerminator = "\\"
 
 func HostRunningOnWindows() bool {
 	return runtime.GOOS == windowsGoOS
@@ -30,8 +34,10 @@ func ToPosix(windowsPath string) (posixPath string) {
 
 func FromPosix(posixPath string) (windowsPath string) {
 	// decode the volume (e.g. /c/<path> --> C:\\) - There should always be a volume name.
+	// The volume may be a UNC path (e.g. /\\localhost\C$\ --> \\localhost\C$\)
 	pathFields := strings.Split(posixPath, "/")
-	volumeName := strings.ToUpper(pathFields[1]) + `:\\`
+	rootPath := strings.ToUpper(pathFields[1])
+	volumeName := AppendRootTerminator(rootPath)
 
 	// translate non-escaped forward slashes into backslashes
 	remainingTranslatedPath := strings.Join(pathFields[2:], "\\")
@@ -39,3 +45,17 @@ func FromPosix(posixPath string) (windowsPath string) {
 	// combine volume name and backslash components
 	return filepath.Clean(volumeName + remainingTranslatedPath)
 }
+
+func AppendRootTerminator(rootPath string) string {
+	// UNC paths start with \\ => \\localhost\
+	// Windows drive paths start with a letter and a colon => C:\
+	// See https://learn.microsoft.com/en-us/dotnet/standard/io/file-path-formats#unc-paths
+	// This function should not be used on file paths since it is meant for root directory paths!
+	if strings.HasSuffix(rootPath, windowsDrivePathTerminator) {
+		return rootPath
+	}
+	if strings.HasPrefix(rootPath, windowsUNCPathPrefix) || strings.HasSuffix(rootPath, windowsDriveColon) {
+		return rootPath + windowsUNCPathTerminator
+	}
+	return rootPath + windowsDrivePathTerminator
+}

syft/internal/windows/path_test.go

@@ -0,0 +1,57 @@
+package windows
+
+import (
+	"testing"
+)
+
+func TestAppendRootTerminator(t *testing.T) {
+	tests := []struct {
+		name   string
+		path   string
+		expect string
+	}{
+		{
+			name:   "NormalUNC",
+			path:   "\\\\localhost\\myserver\\",
+			expect: "\\\\localhost\\myserver\\\\",
+		},
+		{
+			name:   "DriveUNC",
+			path:   "\\\\localhost\\C$\\",
+			expect: "\\\\localhost\\C$\\\\",
+		},
+		{
+			name:   "DriveUNCDirectoryPath",
+			path:   "\\\\localhost\\C$\\Program Files\\Microsoft Visual Studio 10.0\\Common7\\IDE\\PrivateAssemblies\\",
+			expect: "\\\\localhost\\C$\\Program Files\\Microsoft Visual Studio 10.0\\Common7\\IDE\\PrivateAssemblies\\\\",
+		},
+		{
+			name:   "DriveC",
+			path:   "C",
+			expect: "C:\\",
+		},
+		{
+			name:   "DriveC2",
+			path:   "C:",
+			expect: "C:\\",
+		},
+		{
+			name:   "DriveC\\",
+			path:   "C:\\",
+			expect: "C:\\",
+		},
+		{
+			name:   "DriveCDefaultLegacyBehavior",
+			path:   "C:\\Program Files\\Microsoft Visual Studio 10.0\\Common7\\IDE\\PrivateAssemblies\\",
+			expect: "C:\\Program Files\\Microsoft Visual Studio 10.0\\Common7\\IDE\\PrivateAssemblies\\:\\",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := AppendRootTerminator(tt.path)
+			if got != tt.expect {
+				t.Errorf("FromPosix() got = %v, expects %v", got, tt.expect)
+			}
+		})
+	}
+}