flow/util/generate_klayout_tech: write absolute LEF paths for Bazel sandbox

flow/test/test_generate_klayout_tech.py

@@ -130,12 +130,13 @@ def test_basic_generation(self):
 
         self.assertIn("<lef-files>", content)
         self.assertNotIn("original.lef", content)
-        # Path should be relative to results_dir
-        expected_rel = os.path.relpath(
-            os.path.realpath(lef_path),
-            os.path.realpath(self.results_dir),
-        )
-        self.assertIn(expected_rel, content)
+        # LEF paths are written as plain abspath (not relpath, not realpath):
+        # klayout's Layout.read resolves relative <lef-files> entries
+        # against the realpath of the DEF being merged, which under a
+        # Bazel sandbox is the bare execroot -- the in-flight sibling
+        # files only exist in the per-action sandbox.  Absolute paths
+        # bypass the relative-resolution dance.
+        self.assertIn(os.path.abspath(lef_path), content)
 
     def test_with_map_files(self):
         with open(self.template, "w") as f:

flow/util/generate_klayout_tech.py

@@ -51,16 +51,21 @@ def generate_klayout_tech(
     with open(template_lyt, "r") as f:
         content = f.read()
 
-    # Both modes use relative paths from reference_dir, matching the
-    # original sed-based behavior which always uses realpath --relative-to.
-    resolved_lefs = [
-        os.path.relpath(os.path.realpath(f), os.path.realpath(reference_dir))
-        for f in lef_files
-    ]
+    # Write absolute (not relative, not realpath'd) LEF paths into the LYT.
+    # Klayout's Layout.read(def, layout_options) follows the symlinked input
+    # DEF to its realpath at the bare execroot and resolves relative
+    # <lef-files> entries from there.  Sibling intermediates like
+    # objects/klayout_tech.lef don't exist at the bare execroot during
+    # action execution -- they're only at the per-action sandbox -- so
+    # resolution fails with errno=2.  Plain abspath (NOT realpath, which
+    # would chase Bazel input-file symlinks back out to the bare execroot)
+    # keeps klayout pointed at the in-sandbox file.  reference_dir is now
+    # unused for LEFs.
+    resolved_lefs = [os.path.abspath(f) for f in lef_files]
 
     content = replace_lef_files(content, resolved_lefs)
 
-    resolved_maps = [os.path.realpath(f) for f in map_files]
+    resolved_maps = [os.path.abspath(f) for f in map_files]
     content = replace_map_files(content, resolved_maps)
 
     with open(output_lyt, "w") as f: