Keep path to downloaded archive on InstallRequirement

Now we'll be able to transition other parts of the code to use
pre-existing archives directly instead of relying on unpacked sources.

Author: chrahunt

src/pip/_internal/operations/prepare.py

@@ -143,7 +143,7 @@ def unpack_http_url(
     download_dir=None,  # type: Optional[str]
     hashes=None,  # type: Optional[Hashes]
 ):
-    # type: (...) -> None
+    # type: (...) -> str
     temp_dir = TempDirectory(kind="unpack", globally_managed=True)
     # If a download dir is specified, is the file already downloaded there?
     already_downloaded_path = None
@@ -171,6 +171,8 @@ def unpack_http_url(
     ):
         _copy_file(from_path, download_dir, link)
 
+    return from_path
+
 
 def _copy2_ignoring_special_files(src, dest):
     # type: (str, str) -> None
@@ -219,7 +221,7 @@ def unpack_file_url(
     download_dir=None,  # type: Optional[str]
     hashes=None  # type: Optional[Hashes]
 ):
-    # type: (...) -> None
+    # type: (...) -> Optional[str]
     """Unpack link into location.
 
     If download_dir is provided and link points to a file, make a copy
@@ -233,7 +235,7 @@ def unpack_file_url(
         _copy_source_tree(link_path, location)
         if download_dir:
             logger.info('Link is a directory, ignoring download_dir')
-        return
+        return None
 
     # If --require-hashes is off, `hashes` is either empty, the
     # link's embedded hash, or MissingHashes; it is required to
@@ -267,6 +269,8 @@ def unpack_file_url(
     ):
         _copy_file(from_path, download_dir, link)
 
+    return from_path
+
 
 def unpack_url(
     link,  # type: Link
@@ -275,7 +279,7 @@ def unpack_url(
     download_dir=None,  # type: Optional[str]
     hashes=None,  # type: Optional[Hashes]
 ):
-    # type: (...) -> None
+    # type: (...) -> Optional[str]
     """Unpack link.
        If link is a VCS link:
          if only_download, export into download_dir and ignore location
@@ -293,14 +297,15 @@ def unpack_url(
     # non-editable vcs urls
     if link.is_vcs:
         unpack_vcs_link(link, location)
+        return None
 
     # file urls
     elif link.is_file:
-        unpack_file_url(link, location, download_dir, hashes=hashes)
+        return unpack_file_url(link, location, download_dir, hashes=hashes)
 
     # http urls
     else:
-        unpack_http_url(
+        return unpack_http_url(
             link,
             location,
             downloader,
@@ -500,7 +505,7 @@ def prepare_linked_requirement(
                 download_dir = self.wheel_download_dir
 
             try:
-                unpack_url(
+                local_path = unpack_url(
                     link, req.source_dir, self.downloader, download_dir,
                     hashes=hashes,
                 )
@@ -515,6 +520,11 @@ def prepare_linked_requirement(
                     'error {} for URL {}'.format(req, exc, link)
                 )
 
+            # For use in later processing, preserve the file path on the
+            # requirement.
+            if local_path:
+                req.local_file_path = local_path
+
             if link.is_wheel:
                 if download_dir:
                     # When downloading, we only unpack wheels to get

src/pip/_internal/req/req_install.py

@@ -137,6 +137,10 @@ def __init__(
             # PEP 508 URL requirement
             link = Link(req.url)
         self.link = self.original_link = link
+        # Path to any downloaded or already-existing package.
+        self.local_file_path = None  # type: Optional[str]
+        if self.link and self.link.is_file:
+            self.local_file_path = self.link.file_path
 
         if extras:
             self.extras = extras

src/pip/_internal/wheel_builder.py

@@ -460,6 +460,7 @@ def build(
                         )
                         # Update the link for this.
                         req.link = Link(path_to_url(wheel_file))
+                        req.local_file_path = req.link.file_path
                         assert req.link.is_wheel
                         # extract the wheel into the dir
                         unpack_file(req.link.file_path, req.source_dir)