fix: address gemini-code-assist nits on The-OpenROAD-Project#4229

Two follow-ups from gemini-code-assist review of PR The-OpenROAD-Project#4229; the
other five nits no longer apply (three targeted bazel/yosys-check.sh
and bazel/make-yosys-netlist.sh which moved upstream to bazel-orfs
in commit 432edcd63; two were already addressed in commit c18e424
when gds/gds.gz were added and the _export_design_files helper was
factored out).

- flow/designs/design.bzl: make _export_design_files() idempotent
  via a sentinel filegroup. design() and files() both call it, and
  a BUILD file may legitimately call files() more than once (e.g.
  files("verilog") and files("lef") in the same package). A second
  native.exports_files over the same paths is a duplicate-target
  error, so the sentinel short-circuits subsequent calls in the
  same package. The sentinel rule itself is private to the package.

- flow/scripts/synth.sh: capture $(realpath "$2") once into log_file
  rather than re-running it for both the stderr append and the tee
  target in the genElapsedTime.py epilogue.

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

Author: oharboe

flow/designs/design.bzl

@@ -19,6 +19,8 @@ _GROUPS = {
 # gds/gds.gz are inputs in hierarchical flows via ADDITIONAL_GDS.
 _EXPORTED_EXTS = ["v", "sv", "svh", "tcl", "sdc", "def", "cfg", "lef", "lib", "gds", "gds.gz"]
 
+_EXPORTS_SENTINEL = "_orfs_design_exports_sentinel"
+
 def _export_design_files():
     """Publicly export per-file labels for cross-package references.
 
@@ -28,13 +30,26 @@ def _export_design_files():
     resolve only if the source package calls exports_files() on the
     individual files — being part of a public filegroup is not
     sufficient.
+
+    Idempotent: design() and files() both call this, and a BUILD file
+    may legitimately call files() more than once (e.g. files("verilog")
+    and files("lef") in the same package).  A second native.exports_files
+    over the same paths is a duplicate-target error, so a sentinel rule
+    short-circuits subsequent calls within the same package.
     """
+    if _EXPORTS_SENTINEL in native.existing_rules():
+        return
     exported = native.glob(
         ["*.{}".format(e) for e in _EXPORTED_EXTS],
         allow_empty = True,
     )
     if exported:
         native.exports_files(exported, visibility = ["//visibility:public"])
+    native.filegroup(
+        name = _EXPORTS_SENTINEL,
+        srcs = [],
+        visibility = ["//visibility:private"],
+    )
 
 def design(config = "config.mk", user_arguments = [], local_arguments = []):
     """Standard BUILD body for flow/designs/<platform>/<design>/.

flow/scripts/synth.sh

@@ -14,6 +14,7 @@ $PYTHON_EXE "$SCRIPTS_DIR/run_command.py" --log "$(realpath $2)" --append --tee
 # stderr into the log rather than silently dropping it, so a real bug
 # in the helper is still discoverable after the fact.
 stage=$(basename "$2" .log)
+log_file=$(realpath "$2")
 "$PYTHON_EXE" "$UTILS_DIR/genElapsedTime.py" --match "$stage" -d "$LOG_DIR" \
-  2>>"$(realpath "$2")" \
-  | tee -a "$(realpath "$2")" || true
+  2>>"$log_file" \
+  | tee -a "$log_file" || true