From be8b9cb5ecf3f0c518594424cb8cb54003cc9015 Mon Sep 17 00:00:00 2001
From: Mitchell Hentges <mhentges@mozilla.com>
Date: Tue, 3 May 2022 13:40:15 +0000
Subject: [PATCH] Bug 1765361: Only resolve objdir from virtualenv if mozinfo
 not ancestor r=glandium

Virtualenv-based objdir detection doesn't work for instrumented builds,
as instrumentation-specific objdirs aren't created.

Resolve this by:
* Removing redundant cwd-based topsrcdir resolution - the
  `__file__`-based code path below covers this case.
* Only using virtualenv-based resolving if topsrcdir isn't resolved.
* Documenting that virtualenv-based resolution is problematic for
  instrumented builds.

Differential Revision: https://phabricator.services.mozilla.com/D144030
---
 python/mozbuild/mozbuild/base.py | 34 ++++++++++++++++++--------------
 1 file changed, 19 insertions(+), 15 deletions(-)

diff --git a/python/mozbuild/mozbuild/base.py b/python/mozbuild/mozbuild/base.py
index 5644e955fe21..d1f26aaf7ea1 100644
--- a/python/mozbuild/mozbuild/base.py
+++ b/python/mozbuild/mozbuild/base.py
@@ -186,24 +186,28 @@ class MozbuildObject(ProcessExecutionMixin):
                 topsrcdir, topobjdir, mozconfig = load_mozinfo(mozinfo_path)
                 break
 
-            # We choose an arbitrary file as an indicator that this is a
-            # srcdir. We go with ourself because why not!
-            our_path = os.path.join(
-                dir_path, "python", "mozbuild", "mozbuild", "base.py"
-            )
-            if os.path.isfile(our_path):
-                topsrcdir = dir_path
-                break
-
-        # See if we're running from a Python virtualenv that's inside an objdir.
-        mozinfo_path = os.path.join(os.path.dirname(sys.prefix), "../mozinfo.json")
-        if detect_virtualenv_mozinfo and os.path.isfile(mozinfo_path):
-            topsrcdir, topobjdir, mozconfig = load_mozinfo(mozinfo_path)
+        if not topsrcdir:
+            # See if we're running from a Python virtualenv that's inside an objdir.
+            # sys.prefix would look like "$objdir/_virtualenvs/$virtualenv/".
+            # Note that virtualenv-based objdir detection work for instrumented builds,
+            # because they aren't created in the scoped "instrumentated" objdir.
+            # However, working-directory-ancestor-based objdir resolution should fully
+            # cover that case.
+            mozinfo_path = os.path.join(sys.prefix, "..", "..", "mozinfo.json")
+            if detect_virtualenv_mozinfo and os.path.isfile(mozinfo_path):
+                topsrcdir, topobjdir, mozconfig = load_mozinfo(mozinfo_path)
 
         if not topsrcdir:
-            topsrcdir = os.path.abspath(
-                os.path.join(os.path.dirname(__file__), "..", "..", "..")
+            topsrcdir = os.path.normcase(
+                os.path.abspath(
+                    os.path.join(os.path.dirname(__file__), "..", "..", "..")
+                )
             )
+            if sys.platform.startswith("win"):
+                # A bunch of tests depend on the drive letter being capitalized on
+                # Windows. Since the sys.path entries are normcase'd, the __file__
+                # path has a lowercase drive letter. Work around it with capitalize().
+                topsrcdir = topsrcdir.capitalize()
 
         topsrcdir = mozpath.normsep(topsrcdir)
         if topobjdir: