[ARM] Deployment stacks What-If support

src/azure-cli-core/azure/cli/core/commandIndex.latest.json

@@ -212,8 +212,7 @@
       "azure.cli.command_modules.netappfiles"
     ],
     "network": [
-      "azure.cli.command_modules.network",
-      "azure.cli.command_modules.privatedns"
+      "azure.cli.command_modules.network"
     ],
     "policy": [
       "azure.cli.command_modules.policyinsights",
@@ -322,6 +321,9 @@
     "webapp": [
       "azure.cli.command_modules.appservice",
       "azure.cli.command_modules.serviceconnector"
+    ],
+    "stack-whatif": [
+      "azure.cli.command_modules.resource"
     ]
   }
 }

src/azure-cli-core/azure/cli/core/helpIndex.latest.json

@@ -366,6 +366,10 @@
       "webapp": {
         "summary": "Manage web apps.",
         "tags": ""
+      },
+      "stack-whatif": {
+        "summary": "A deployment stack What-If is a preview of an operation to be performed on a new or existing deployment stack.",
+        "tags": ""
       }
     },
     "commands": {

src/azure-cli/azure/cli/command_modules/resource/_color.py

@@ -12,6 +12,7 @@ class Color(Enum):
     GREEN = "\033[38;5;77m"
     PURPLE = "\033[38;5;141m"
     BLUE = "\033[38;5;39m"
+    CYAN = "\033[38;5;51m"
     GRAY = "\033[38;5;246m"
     RED = "\033[38;5;203m"
     DARK_YELLOW = "\033[38;5;136m"
@@ -26,11 +27,15 @@ def __init__(self, enable_color=True):
         self._enable_color = enable_color
         self._contents = []
         self._colors = deque()
+        self._indents = []
 
     def build(self):
         return "".join(self._contents)
 
-    def append(self, value, color=None):
+    def append(self, value, color=None, no_indent=False):
+        if not no_indent and self._should_indent():
+            self._contents.append(''.join(self._indents))
+
         if color:
             self._push_color(color)
 
@@ -41,14 +46,55 @@ def append(self, value, color=None):
 
         return self
 
-    def append_line(self, value="", color=None):
-        self.append(f"{str(value)}\n", color)
-
-        return self
+    def append_line(self, value="", color=None, no_indent=False):
+        self.append(value, color, no_indent)
+        return self.append("\n", no_indent=True)
 
     def new_color_scope(self, color):
         return self.ColorScope(self, color)
 
+    def insert(self, index, value="", color=None, no_indent=False):
+        if color and self._enable_color:
+            self._contents.insert(index, str(Color.RESET))
+
+        self._contents.insert(index, str(value))
+
+        if color and self._enable_color:
+            self._contents.insert(index, str(color))
+
+        if not no_indent and self._should_indent(index, True):
+            self._contents.insert(index, ''.join(self._indents))
+
+        return self
+
+    def insert_line(self, index, value="", color=None, no_indent=False):
+        self.insert(index, "\n", no_indent=no_indent)
+        return self.insert(index, value, color, no_indent)
+
+    def get_current_index(self):
+        return len(self._contents)
+
+    def push_indent(self, indent):
+        self._indents.append(indent)
+
+    def pop_indent(self):
+        self._indents.pop()
+
+    def ensure_num_new_lines(self, num_new_lines):
+        if len(self._contents) == 0:
+            self.append("\n" * num_new_lines)
+            return
+
+        last_entry = self._contents[-1]
+        existing_newlines = len(last_entry) - len(last_entry.rstrip('\n'))
+        remaining_newlines = num_new_lines - existing_newlines
+
+        if remaining_newlines > 0:
+            self._contents.append("\n" * remaining_newlines)
+
+    def clear(self):
+        self._contents = []
+
     def _push_color(self, color):
         if not self._enable_color:
             return
@@ -63,6 +109,10 @@ def _pop_color(self):
         self._colors.pop()
         self._contents.append(str(self._colors[-1] if self._colors else Color.RESET))
 
+    def _should_indent(self, index=-1, is_insert=False):
+        return len(self._indents) > 0 and (
+            not self._contents or self._contents[max(index - 1, 0) if is_insert else index].endswith("\n"))
+
     # pylint: disable=protected-access
     class ColorScope:
         def __init__(self, color_string_builder, color):

src/azure-cli/azure/cli/command_modules/resource/_formatters.py

@@ -226,7 +226,8 @@ def _format_resource_changes(builder, resource_changes, definite_changes=True):
     for _, resource_changes_in_scope in resource_changes_by_scope:
         resource_changes_in_scope_list = list(resource_changes_in_scope)
         scope = _get_scope(resource_changes_in_scope_list[0])
-        _format_resource_changes_in_scope(builder, scope, resource_changes_in_scope_list)
+        if scope != "Unknown":
+            _format_resource_changes_in_scope(builder, scope, resource_changes_in_scope_list)
 
 
 def _format_resource_changes_in_scope(builder, scope, resource_changes_in_scope):
@@ -248,6 +249,9 @@ def _format_resource_changes_in_scope(builder, scope, resource_changes_in_scope)
 def _format_resource_change(builder, resource_change, is_last):
     change_type = resource_change.change_type
     relative_resource_id = _get_relative_resource_id(resource_change)
+    if relative_resource_id is None:
+        return
+
     api_version = _get_api_version(resource_change)
 
     builder.append_line()
@@ -447,7 +451,7 @@ def _get_api_version(resource_change):
 
 def _get_scope(resource_change):
     scope, _ = split_resource_id(resource_change.resource_id)
-    return scope
+    return scope or "Unknown"  # TODO: extensible resource support
 
 
 def _get_scope_uppercase(resource_change):