Backed out changeset 738ee02dfc2a (bug 1802405) for causing build bustages. CLOSED TREE

build/mach_initialize.py

@@ -116,9 +116,11 @@ def _maybe_activate_mozillabuild_environment():
 
     paths_to_add = [mozillabuild_msys_tools_path, mozillabuild / "bin"]
     existing_paths = [Path(p) for p in os.environ.get("PATH", "").split(os.pathsep)]
+    # It's important that we prepend to the path rather than append,
+    # in case mach is getting called from another msys2 environment.
     for new_path in paths_to_add:
         if new_path not in existing_paths:
-            os.environ["PATH"] += f"{os.pathsep}{new_path}"
+            os.environ["PATH"] = f"{new_path}{os.pathsep}" + os.environ["PATH"]
 
 
 def initialize(topsrcdir):