Always treat host FS as case-insensitive to produce deterministic sys…

…tem libraries regardless of OS (#23426)

Fixes #23379

tools/system_libs.py

@@ -219,7 +219,6 @@ def create_ninja_file(input_files, filename, libname, cflags, asflags=None, cust
   suffix = shared.suffix(libname)
   build_dir = os.path.dirname(filename)
 
-  case_insensitive = is_case_insensitive(os.path.dirname(filename))
   if suffix == '.o':
     assert len(input_files) == 1
     input_file = escape_ninja_path(input_files[0])
@@ -229,12 +228,11 @@ def create_ninja_file(input_files, filename, libname, cflags, asflags=None, cust
   else:
     objects = []
     for src in input_files:
-      # Resolve duplicates by appending unique.
-      # This is needed on case insensitive filesystem to handle,
-      # for example, _exit.o and _Exit.o.
-      object_basename = shared.unsuffixed_basename(src)
-      if case_insensitive:
-        object_basename = object_basename.lower()
+      # Resolve duplicates by appending unique. This is needed on case
+      # insensitive filesystem to handle, for example, _exit.o and _Exit.o.
+      # This is done even on case sensitive filesystem so that builds are
+      # reproducible across platforms.
+      object_basename = shared.unsuffixed_basename(src).lower()
       o = os.path.join(build_dir, object_basename + '.o')
       object_uuid = 0
       # Find a unique basename
@@ -270,14 +268,6 @@ def create_ninja_file(input_files, filename, libname, cflags, asflags=None, cust
   ensure_target_in_ninja_file(get_top_level_ninja_file(), f'subninja {escape_ninja_path(filename)}')
 
 
-def is_case_insensitive(path):
-  """Returns True if the filesystem at `path` is case insensitive."""
-  utils.write_file(os.path.join(path, 'test_file'), '')
-  case_insensitive = os.path.exists(os.path.join(path, 'TEST_FILE'))
-  os.remove(os.path.join(path, 'test_file'))
-  return case_insensitive
-
-
 class Library:
   """
   `Library` is the base class of all system libraries.
@@ -490,7 +480,6 @@ def build_objects(self, build_dir):
     commands = []
     objects = set()
     cflags = self.get_cflags()
-    case_insensitive = is_case_insensitive(build_dir)
     for src in self.get_files():
       ext = shared.suffix(src)
       if ext in {'.s', '.S', '.c'}:
@@ -507,15 +496,12 @@ def build_objects(self, build_dir):
         cmd += cflags
       cmd = self.customize_build_cmd(cmd, src)
 
-      object_basename = shared.unsuffixed_basename(src)
-      if case_insensitive:
-        object_basename = object_basename.lower()
+      object_basename = shared.unsuffixed_basename(src).lower()
       o = os.path.join(build_dir, object_basename + '.o')
       if o in objects:
-        # If we have seen a file with the same name before, we are on a case-insensitive
-        # filesystem and need a separate command to compile this file with a
-        # custom unique output object filename, as batch compile doesn't allow
-        # such customization.
+        # If we have seen a file with the same name before, we need a separate
+        # command to compile this file with a custom unique output object
+        # filename, as batch compile doesn't allow such customization.
         #
         # This is needed to handle, for example, _exit.o and _Exit.o.
         object_uuid = 0
@@ -530,6 +516,8 @@ def build_objects(self, build_dir):
         src = os.path.relpath(src, build_dir)
         src = utils.normalize_path(src)
         batches.setdefault(tuple(cmd), []).append(src)
+        # No -o in command, use original file name.
+        o = os.path.join(build_dir, shared.unsuffixed_basename(src) + '.o')
       else:
         commands.append(cmd + [src, '-o', o])
       objects.add(o)