DRAFT - pip install --dry-run

src/pip/_internal/commands/install.py

@@ -239,6 +239,18 @@ def add_options(self) -> None:
             ),
         )
 
+        self.cmd_opts.add_option(
+            "--dry-run",
+            action="store_true",
+            dest="dry_run",
+            default=False,
+            help=(
+                "Don't actually install anything, just print what would be. "
+                "Can be used in combination with --report and --ignore-installed "
+                "to 'resolve' the requirements."
+            ),
+        )
+
         self.cmd_opts.add_option(cmdoptions.no_binary())
         self.cmd_opts.add_option(cmdoptions.only_binary())
         self.cmd_opts.add_option(cmdoptions.prefer_binary())
@@ -361,6 +373,10 @@ def run(self, options: Values, args: List[str]) -> int:
                 with open(options.json_report_file, "w") as f:
                     json.dump(report.to_json(), f)
 
+            if options.dry_run:
+                # TODO print something useful here
+                return SUCCESS
+
             try:
                 pip_req = requirement_set.get_requirement("pip")
             except KeyError: