support missing drive letters in PS path type

lib/ansible/module_utils/powershell/Ansible.ModuleUtils.Legacy.psm1

@@ -207,7 +207,17 @@ Function Get-AnsibleParam($obj, $name, $default = $null, $resultobj = @{}, $fail
             $value = Expand-Environment($value)
             # Test if a valid path is provided
             if (-not (Test-Path -IsValid $value)) {
-                Fail-Json -obj $resultobj -message "Get-AnsibleParam: Parameter '$name' has an invalid path '$value' specified."
+                $path_invalid = $true
+                # could still be a valid-shaped path with a nonexistent drive letter
+                if ($value -match "^\w:") {
+                    # rewrite path with a valid drive letter and recheck the shape- this might still fail, eg, a nonexistent non-filesystem PS path
+                    if (Test-Path -IsValid $(@(Get-PSDrive -PSProvider Filesystem)[0].Name + $value.Substring(1))) {
+                        $path_invalid = $false
+                    }
+                }
+                if ($path_invalid) {
+                    Fail-Json -obj $resultobj -message "Get-AnsibleParam: Parameter '$name' has an invalid path '$value' specified."
+                }
             }
         } elseif ($type -eq "str") {
             # Convert str types to real Powershell strings

test/integration/targets/win_module_utils_legacy/aliases

@@ -0,0 +1,2 @@
+windows/ci/group1
+windows/ci/smoketest

test/integration/targets/win_module_utils_legacy/library/testpath.ps1

@@ -0,0 +1,9 @@
+#powershell
+
+#Requires -Module Ansible.ModuleUtils.Legacy
+
+$params = Parse-Args $args
+
+$path = Get-AnsibleParam -Obj $params -Name path -Type path
+
+Exit-Json @{ path=$path }

test/integration/targets/win_module_utils_legacy/tasks/main.yml

@@ -0,0 +1,23 @@
+# NB: these tests are just a placeholder until we have pester unit tests.
+# They are being run as part of the Windows smoke tests. Please do not significantly
+# increase the size of these tests, as the smoke tests need to remain fast.
+# Any significant additions should be made to the (as yet nonexistent) PS module_utils unit tests.
+
+- name: find a nonexistent drive letter
+  raw: foreach($c in [char[]]([char]'D'..[char]'Z')) { If (-not $(Get-PSDrive $c -ErrorAction SilentlyContinue)) { return $c } }
+  register: bogus_driveletter
+
+- assert:
+    that: bogus_driveletter.stdout_lines[0] | length == 1
+
+- name: test path shape validation
+  testpath:
+    path: "{{ item.path }}"
+  failed_when: path_shapes | failed != (item.should_fail | default(false))
+  register: path_shapes
+  with_items:
+  - path: C:\Windows
+  - path: HKLM:\Software
+  - path: '{{ bogus_driveletter.stdout_lines[0] }}:\goodpath'
+  - path: '{{ bogus_driveletter.stdout_lines[0] }}:\badpath*%@:\blar'
+    should_fail: true