Add --report option to pip install

Author: sbidoul

news/53.feature.rst

@@ -0,0 +1,3 @@
+Add ``--report`` to the install command to generate a json report of what was installed.
+In combination with ``--dry-run`` and ``--ignore-installed`` it can be used to resolve
+the requirements.

src/pip/_internal/commands/install.py

@@ -1,4 +1,5 @@
 import errno
+import json
 import operator
 import os
 import shutil
@@ -21,6 +22,7 @@
 from pip._internal.locations import get_scheme
 from pip._internal.metadata import get_environment
 from pip._internal.models.format_control import FormatControl
+from pip._internal.models.installation_report import InstallationReport
 from pip._internal.operations.build.build_tracker import get_build_tracker
 from pip._internal.operations.check import ConflictDetails, check_install_conflicts
 from pip._internal.req import install_given_reqs
@@ -250,6 +252,19 @@ def add_options(self) -> None:
         self.parser.insert_option_group(0, index_opts)
         self.parser.insert_option_group(0, self.cmd_opts)
 
+        self.cmd_opts.add_option(
+            "--report",
+            dest="json_report_file",
+            metavar="file",
+            default=None,
+            help=(
+                "Generate a JSON file describing what pip did to install "
+                "the provided requirements. "
+                "Can be used in combination with --dry-run and --ignore-installed "
+                "to 'resolve' the requirements."
+            ),
+        )
+
     @with_cleanup
     def run(self, options: Values, args: List[str]) -> int:
         if options.use_user_site and options.target_dir is not None:
@@ -352,6 +367,10 @@ def run(self, options: Values, args: List[str]) -> int:
             requirement_set = resolver.resolve(
                 reqs, check_supported_wheels=not options.target_dir
             )
+            if options.json_report_file:
+                report = InstallationReport(requirement_set)
+                with open(options.json_report_file, "w") as f:
+                    json.dump(report.to_dict(), f)
 
             if options.dry_run:
                 items = [

src/pip/_internal/models/installation_report.py

@@ -0,0 +1,37 @@
+from typing import Any, Dict
+
+from pip._internal.req.req_install import InstallRequirement
+from pip._internal.req.req_set import RequirementSet
+
+
+class InstallationReport:
+    def __init__(self, req_set: RequirementSet):
+        self._req_set = req_set
+
+    @classmethod
+    def _install_req_to_dict(cls, ireq: InstallRequirement) -> Dict[str, Any]:
+        assert ireq.download_info, f"No download_info for {ireq}"
+        res = {
+            # PEP 610 json for the download URL
+            "download_info": ireq.download_info.to_dict(),
+            # is_direct is true if the requirement was a direct URL reference (which
+            # includes editable requirements), and false if the requirement was
+            # downloaded from a PEP 503 index or --find-links.
+            "is_direct": bool(ireq.original_link),
+            # requested is true if the requirement was specified by the user (aka
+            # top level requirement), and false if it was installed as a dependency of a
+            # requirement. https://peps.python.org/pep-0376/#requested
+            "requested": ireq.user_supplied,
+            # PEP 566 json encoding for metadata
+            # https://www.python.org/dev/peps/pep-0566/#json-compatible-metadata
+            "metadata": ireq.get_dist().json_metadata,
+        }
+        return res
+
+    def to_dict(self) -> Dict[str, Any]:
+        return {
+            "install": {
+                name: self._install_req_to_dict(ireq)
+                for name, ireq in self._req_set.requirements.items()
+            }
+        }