pip.py falls back to virtualenv pip/python

src/rez/pip.py

@@ -7,6 +7,8 @@
 from rez.vendor.distlib.markers import interpret
 from rez.vendor.distlib.util import parse_name_and_version
 from rez.vendor.enum.enum import Enum
+from rez.vendor.packaging.version import Version as PackagingVersion
+from rez.vendor.packaging.specifiers import Specifier
 from rez.vendor.six.six import StringIO
 from rez.resolved_context import ResolvedContext
 from rez.utils.execution import Popen
@@ -31,6 +33,9 @@
 from textwrap import dedent
 
 
+PIP_SPECIFIER = Specifier(">=19")  # rez pip only compatible with pip>=19
+
+
 class InstallMode(Enum):
     # don't install dependencies. Build may fail, for example the package may
     # need to compile against a dependency. Will work for pure python though.
@@ -81,31 +86,35 @@ def find_pip(pip_version=None, python_version=None):
     """
     py_exe = None
     context = None
+    found_pip_version = None
 
-    py_exe, pip_version, context = find_pip_from_context(
-        python_version,
-        pip_version=pip_version
-    )
-
-    if not py_exe:
-        py_exe, pip_version, context = find_pip_from_context(
-            python_version,
-            pip_version=pip_version or "latest"
-        )
+    for version in [pip_version, pip_version or "latest"]:
+        try:
+            py_exe, found_pip_version, context = find_pip_from_context(
+                python_version,
+                pip_version=version
+            )
+            if _check_found(py_exe, found_pip_version):
+                break
+        except BuildError as error:
+            print_warning(str(error))
 
-    if not py_exe:
+    else:  # No break from: for version in [pip_version,...]
         import pip
-        pip_version = pip.__version__
+        found_pip_version = pip.__version__
         py_exe = sys.executable
-        print_warning(
-            "Found no pip in python and pip package; "
-            "falling back to pip installed in rez own virtualenv (version %s)",
-            pip_version
+        print_warning("Found no pip in any python and/or pip packages!")
+        print_warning("Falling back to pip installed in rez own virtualenv:")
+        logging_arguments = (
+            ("pip", found_pip_version, pip.__file__),
+            ("python", ".".join(map(str, sys.version_info[:3])), py_exe),
         )
+        for warn_args in logging_arguments:
+            print_warning("%10s: %s (%s)", *warn_args)
 
-    pip_major = pip_version.split('.')[0]
-    if int(pip_major) < 19:
-        raise RezSystemError("pip >= 19 is required! Please update your pip.")
+    if not _check_found(py_exe, found_pip_version, log_invalid=False):
+        message = "pip{specifier} is required! Please update your pip."
+        raise RezSystemError(message.format(specifier=PIP_SPECIFIER))
 
     return py_exe, context
 
@@ -559,6 +568,34 @@ def _cmd(context, command):
         raise BuildError("Failed to download source with pip: %s" % cmd_str)
 
 
+def _check_found(py_exe, version_text, log_invalid=True):
+    """Check the Python and pip version text found.
+
+    Args:
+        py_exe (str or None): Python executable path found, if any.
+        version_text (str or None): Pip version found, if any.
+        log_invalid (bool): Whether to log messages if found invalid.
+
+    Returns:
+        bool: Python is OK and pip version fits against ``PIP_SPECIFIER``.
+    """
+    is_valid = True
+    message = "Needs pip%s, but found '%s' for Python '%s'"
+
+    if version_text is None or not py_exe:
+        is_valid = False
+        if log_invalid:
+            print_debug(message, PIP_SPECIFIER, version_text, py_exe)
+
+
+    elif PackagingVersion(version_text) not in PIP_SPECIFIER:
+        is_valid = False
+        if log_invalid:
+            print_warning(message, PIP_SPECIFIER, version_text, py_exe)
+
+    return is_valid
+
+
 _verbose = config.debug("package_release")