fix(generate_klayout_tech): drop realpath() — breaks Bazel sandbox

os.path.realpath() follows symlinks.  Inside a Bazel sandbox, the
bazel-out/ tree is symlinked from the sandbox back to the bare
execroot; realpath resolves through that symlink and yields the
bare-execroot path, not the sandbox path.

That alone doesn't matter for os.path.relpath(a, b) when both
operands are realpath'd from the same sandbox — the relative
result is unchanged.  But the resulting <lef-files> path in the
generated klayout.lyt is later resolved by klayout against the LYT
file's location.  Klayout opens the LYT (also through a symlink),
resolves through to the bare execroot, and then looks for the
sibling klayout_tech.lef at the bare-execroot path — where the
in-flight file does not exist during action execution (only the
sandbox copy does), so def2stream fails with errno=2.

Fix: don't realpath.  os.path.relpath produces the correct relative
path from sandbox-relative inputs directly.  Map files keep their
absolute form via abspath for the unchanged-under-non-sandbox case.

Surfaced for the first time on bazelisk build
//flow/designs/sky130hd/gcd:gcd_final_blender_html — the
orfs_blender macro is the first bazel-side consumer of orfs_gds
(klayout def2stream), so the latent path bug had no prior trigger.

Mirrors bazel-orfs's patches/0037-fix-generate_klayout_tech-drop-realpath.patch
into ORFS directly so bazel-orfs no longer needs to carry it.

Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>

Author: oharboe

flow/util/generate_klayout_tech.py

@@ -51,16 +51,15 @@ 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
-    ]
+    # Compute relpath without realpath(): under a Bazel sandbox, bazel-out/
+    # entries are symlinks to the bare execroot; realpath follows them and
+    # makes the generated LYT reference files at the bare-execroot path,
+    # where in-flight outputs do not exist during action execution.
+    resolved_lefs = [os.path.relpath(f, reference_dir) 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: