Bazel cleanup (#7114)

## Summary

This PR does a small round of Bazel 7 cleanup and dependency-wiring
simplification on top of the already-working Bazel 7 / protobuf 6
baseline.

The goal is not to change dependency versions or CI behavior, but to
reduce migration-specific scaffolding where it is no longer needed, keep
the remaining shims clearly documented, and preserve a clean, working
build/test state.

## What changed

### Repository helper cleanup
- simplified `third_party/repo.bzl`
- removed unused `tb_http_archive` support for `build_file` /
`link_files`
- kept `tb_http_archive` focused on the behaviors still used in this
repo:
  - mirrored URLs
  - optional patch application

### WORKSPACE cleanup
- switched mirror-only repositories back to plain `http_archive` where
the TensorBoard-specific helper was no longer adding value
- kept `tb_http_archive(...)` only for repositories that still need:
  - patch application
  - repo mapping
- clarified comments around the remaining Bazel/protobuf compatibility
repos

### Compatibility shim review
- verified that `third_party/compatibility_proxy` is still required by
the current `rules_java` / protobuf loading path
- kept it in place rather than removing a live dependency
- verified that `third_party/protobuf_pip_deps` and
`third_party/protobuf_pip_deps_setuptools` are still required by
protobuf 6.31.1’s Bazel macros and Python packaging flow
- improved documentation explaining why those repos still exist

## Why this PR is useful

This PR keeps the Bazel 7 migration easier to maintain by:
- removing dead helper code
- narrowing custom repository logic to the cases that still need it
- documenting the remaining compatibility shims with concrete rationale
- avoiding behavior changes to the working build graph

## Validation

Validated with:
- `bazel fetch //tensorboard/...`
- `bazel build //tensorboard/... --nobuild`
- `bazel build //tensorboard/...`
- `bazel test //tensorboard/plugins/debugger_v2:debugger_v2_plugin_test`
- full local Bazel test runs after the cleanup changes

Author: psamanoelton

WORKSPACE

@@ -293,7 +293,7 @@ tb_http_archive(
     urls = tb_mirror_urls("https://github.com/bazelbuild/rules_cc/archive/refs/tags/0.1.0.tar.gz"),
 )
 
-tb_http_archive(
+http_archive(
     name = "tb_rules_java",
     sha256 = "b2519fabcd360529071ade8732f208b3755489ed7668b118f8f90985c0e51324",
     strip_prefix = "rules_java-8.6.1",
@@ -305,11 +305,17 @@ local_repository(
     path = "third_party/compatibility_proxy",
 )
 
+# Protobuf 6.31.1 still expects a pip-style requirements helper repo from its
+# WORKSPACE macros. TensorBoard only needs the narrow `install_deps()` /
+# `requirement()` surface that protobuf actually loads in this configuration.
 local_repository(
     name = "protobuf_pip_deps",
     path = "third_party/protobuf_pip_deps",
 )
 
+# Protobuf's python/dist BUILD also references
+# `external/protobuf_pip_deps_setuptools/site-packages`, so keep this separate
+# repo shape even though it only vendors an empty placeholder tree here.
 local_repository(
     name = "protobuf_pip_deps_setuptools",
     path = "third_party/protobuf_pip_deps_setuptools",
@@ -350,14 +356,14 @@ protobuf_deps()
 #
 # Keep this aligned with TensorFlow 2.21's Bazel-side gRPC dependency so the
 # grpc plugin and protobuf repository stay on a known-compatible combination.
-tb_http_archive(
+http_archive(
     name = "com_github_grpc_grpc",
     sha256 = "dd6a2fa311ba8441bbefd2764c55b99136ff10f7ea42954be96006a2723d33fc",
     strip_prefix = "grpc-1.74.0",
     urls = tb_mirror_urls("https://github.com/grpc/grpc/archive/refs/tags/v1.74.0.tar.gz"),
 )
 
-tb_http_archive(
+http_archive(
     name = "build_bazel_rules_swift",
     sha256 = "9919ed1d8dae509645bfd380537ae6501528d8de971caebed6d5185b9970dc4d",
     urls = tb_mirror_urls("https://github.com/bazelbuild/rules_swift/releases/download/2.1.1/rules_swift.2.1.1.tar.gz"),

tensorboard/plugins/debugger_v2/debugger_v2_plugin_test.py

@@ -1494,7 +1494,7 @@ def testServeSourceFileContentOfThisTestFile(self):
         data = json.loads(response.get_data())
         self.assertEqual(data["host_name"], _HOST_NAME)
         self.assertEqual(data["file_path"], _CURRENT_FILE_FULL_PATH)
-        with open(__file__, "r") as f:
+        with open(__file__, "r", newline="") as f:
             lines = f.read().split("\n")
         self.assertEqual(data["lines"], lines)
 

third_party/protobuf_pip_deps/requirements.bzl

@@ -3,7 +3,11 @@
 Protobuf's Bazel macros load a pip-style requirements helper that provides
 `requirement()` and `install_deps()`. TensorBoard only needs a very small
 subset of that surface here, so this file supplies just the labels
-protobuf actually asks for here.
+protobuf 6.31.1 actually asks for here:
+
+* `install_deps()` from protobuf's WORKSPACE setup
+* `requirement("setuptools")` from `python/dist/BUILD.bazel`
+* `requirement("numpy")` from protobuf's numpy test target
 """
 
 def requirement(name):
@@ -15,5 +19,5 @@ def requirement(name):
     fail("Unsupported protobuf pip dependency: %s" % name)
 
 def install_deps():
-    """Compatibility no-op for callers that expect an install_deps symbol."""
+    """Compatibility no-op for protobuf's WORKSPACE dependency hook."""
     return None

third_party/protobuf_pip_deps_setuptools/BUILD.bazel

@@ -1,3 +1,6 @@
+# Protobuf's python/dist wheel genrule exports this exact external repo path on
+# PYTHONPATH, so preserve the repo/target shape even though TensorBoard only
+# needs an empty placeholder tree here.
 filegroup(
     name = "site_packages",
     srcs = glob(["site-packages/**"]),

third_party/repo.bzl

@@ -23,17 +23,8 @@ def tb_mirror_urls(url):
         url,
     ]
 
-def _get_link_dict(ctx, link_files, build_file):
-    """Builds the destination->source map for files linked into a repo rule."""
-    link_dict = {ctx.path(v): ctx.path(Label(k)) for k, v in link_files.items()}
-    if build_file:
-        link_dict[ctx.path("BUILD.bazel")] = ctx.path(Label(build_file))
-    return link_dict
-
 def _tb_http_archive_impl(ctx):
-    """Repository-rule implementation with optional patching and linked files."""
-    link_dict = _get_link_dict(ctx, ctx.attr.link_files, ctx.attr.build_file)
-
+    """Repository-rule implementation with optional patching."""
     patch_files = ctx.attr.patch_file
     # Resolve patch labels up front so Bazel reports missing patch inputs before
     # download/extract work has completed.
@@ -53,11 +44,6 @@ def _tb_http_archive_impl(ctx):
         if patch_file:
             ctx.patch(patch_file, strip = 1)
 
-    # Link in any repository-local BUILD/link files after extraction and patching.
-    for dst, src in link_dict.items():
-        ctx.delete(dst)
-        ctx.symlink(src, dst)
-
 _tb_http_archive = repository_rule(
     implementation = _tb_http_archive_impl,
     attrs = {
@@ -66,13 +52,11 @@ _tb_http_archive = repository_rule(
         "strip_prefix": attr.string(),
         "type": attr.string(),
         "patch_file": attr.string_list(),
-        "build_file": attr.string(),
-        "link_files": attr.string_dict(),
     },
 )
 
 def tb_http_archive(name, sha256, urls, **kwargs):
-    """Downloads a mirrored archive and creates a TensorBoard external repo."""
+    """Downloads a mirrored archive for TensorBoard-specific repo wiring."""
     if len(urls) < 2:
         fail("tb_http_archive(urls) must have redundant URLs.")