install report: add suport for stdout output

Author: sbidoul

src/pip/_internal/commands/install.py

@@ -4,6 +4,7 @@
 import os
 import shutil
 import site
+import sys
 from optparse import SUPPRESS_HELP, Values
 from typing import Iterable, List, Optional
 
@@ -261,7 +262,8 @@ def add_options(self) -> None:
                 "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."
+                "to 'resolve' the requirements. "
+                "When - is used as file name it writes to stdout."
             ),
         )
 
@@ -370,8 +372,11 @@ def run(self, options: Values, args: List[str]) -> int:
 
             if options.json_report_file:
                 report = InstallationReport(requirement_set.requirements_to_install)
-                with open(options.json_report_file, "w", encoding="utf-8") as f:
-                    json.dump(report.to_dict(), f)
+                if options.json_report_file == "-":
+                    json.dump(report.to_dict(), sys.stdout, indent=2, ensure_ascii=True)
+                else:
+                    with open(options.json_report_file, "w", encoding="utf-8") as f:
+                        json.dump(report.to_dict(), f, indent=2, ensure_ascii=False)
 
             if options.dry_run:
                 would_install_items = sorted(

tests/functional/test_install_report.py

@@ -175,3 +175,24 @@ def test_install_report_vcs_editable(
         "/src/pip-test-package"
     )
     assert pip_test_package_report["download_info"]["dir_info"]["editable"] is True
+
+
+@pytest.mark.usefixtures("with_wheel")
+def test_install_report_to_stdout(
+    script: PipTestEnvironment, shared_data: TestData
+) -> None:
+    result = script.pip(
+        "install",
+        "simplewheel",
+        "--quiet",
+        "--dry-run",
+        "--no-index",
+        "--find-links",
+        str(shared_data.root / "packages/"),
+        "--report",
+        "-",
+    )
+    assert not result.stderr
+    report = json.loads(result.stdout)
+    assert "install" in report
+    assert len(report["install"]) == 1