Hooks: Conda: Use Conda's metadata to identify binary dependencies.

Anaconda breaks packages up, moving DLLs out of the package into an
environment-wide shared `bin` folder. Our collect_dynamic_libs() doesn't
collect them because it searches inside a package's installation. Because all
DLLs from all packages go in a single shared folder (and because they're
generally named something non-descript like `libgimt45b1ab87b2`), we currently
have to hand- label long lists of constantly shifting dependencies (determined
imperically with terrible success-rates). See issue
\#5076#issuecomment-683436017 for the full magnitude of this problem.

Fortunatley, Conda keeps a record of which files belong to which package in a
`conda-meta` folder. Parsing the contents gives the list of DLLs we need.

Currently, this is exposed as a hook utility and not used by default. Partly
because the metadata is referenced by distribution name rather than package
name e.g. pillow rather than PIL. If we were to make this automatic then we'd
need to provide a mapping from one to the other.

This also drags in a lot of junk and building and testing files. But these
should be addressed by the conda distribution authors as they bloat the
unfrozen packages too. Certainly, we don't want to be guessing file filters
ourselves. In my experience, Conda users don't seem too concerned about
filesize so I don't think we should worry about it either.

PyInstaller/compat.py

@@ -159,6 +159,11 @@
 # https://stackoverflow.com/questions/47610844#47610844
 is_conda = os.path.isdir(os.path.join(base_prefix, 'conda-meta'))
 
+# Similar to ``is_conda`` but is ``False`` using another ``venv``-like manager
+# on top. In this case, no packages encountered will be conda packages meaning
+# that the default non-conda behaviour is generally desired from PyInstaller.
+is_pure_conda = os.path.isdir(os.path.join(sys.prefix, 'conda-meta'))
+
 # In Python 3.4 module 'imp' is deprecated and there is another way how
 # to obtain magic value.
 import importlib.util

PyInstaller/utils/hooks/__init__.py

@@ -19,7 +19,7 @@
 
 from ...compat import base_prefix, exec_command_stdout, exec_python, \
     exec_python_rc, is_darwin, is_venv, string_types, open_file, \
-    EXTENSION_SUFFIXES, ALL_SUFFIXES
+    EXTENSION_SUFFIXES, ALL_SUFFIXES, is_conda, is_pure_conda
 from ... import HOMEPATH
 from ... import log as logging
 from ...exceptions import ExecCommandFailed
@@ -1134,6 +1134,17 @@ def collect_all(
     return datas, binaries, hiddenimports
 
 
+if is_pure_conda:
+    from . import conda as conda_support  # noqa: F401
+elif is_conda:
+    from .conda import CONDA_META_DIR as _tmp
+    logger.warning(
+        "Assuming this isn't an Anaconda environment or an additional venv/"
+        "pipenv/... environment manager is being used on top because the "
+        "conda-meta folder %s doesn't exist.", _tmp)
+    del _tmp
+
+
 # These imports need to be here due to these modules recursively importing this module.
 from .django import *
 from .gi import *