[build] Add tools to generate compile_commands.json (ray-project#25180

)

We want to use `clangd` as the language server.

`clangd` is an awesome language server that has many features and is very accurate.

But it needs a `compile_commands.json` to work.

This PR adds a popular bazel rule to generate this file.

.gitignore

@@ -213,3 +213,11 @@ workflow_data/
 
 # Jupyter Notebooks
 **/.ipynb_checkpoints/
+
+### Added by Hedron's Bazel Compile Commands Extractor: https://github.com/hedronvision/bazel-compile-commands-extractor
+# The external link: Differs on Windows vs macOS/Linux, so we can't check it in. The pattern needs to not have a trailing / because it's a symlink on macOS/Linux.
+/external
+# Compiled output -> don't check in
+/compile_commands.json
+# Directory where clangd puts its indexing work
+/.cache/

WORKSPACE

@@ -20,3 +20,9 @@ load("@bazel_skylib//lib:versions.bzl", "versions")
 # When the bazel version is updated, make sure to update it
 # in setup.py as well.
 versions.check(minimum_bazel_version = "4.2.1")
+
+# Tools to generate `compile_commands.json` to enable awesome tooling of the C language family.
+# Just run `bazel run @hedron_compile_commands//:refresh_all`
+load("@hedron_compile_commands//:workspace_setup.bzl", "hedron_compile_commands_setup")
+
+hedron_compile_commands_setup()

bazel/ray_deps_setup.bzl

@@ -306,3 +306,16 @@ def ray_deps_setup():
         ],
         sha256 = "379113459b0feaf6bfbb584a91874c065078aa673222846ac765f86661c27407",
     )
+
+    # Hedron's Compile Commands Extractor for Bazel
+    # https://github.com/hedronvision/bazel-compile-commands-extractor
+    http_archive(
+        name = "hedron_compile_commands",
+
+        # Replace the commit hash in both places (below) with the latest, rather than using the stale one here.
+        # Even better, set up Renovate and let it do the work for you (see "Suggestion: Updates" in the README).
+        url = "https://github.com/hedronvision/bazel-compile-commands-extractor/archive/cfd16a16cb4c4f27337ef652aa8510dcf1dd01ce.tar.gz",
+        strip_prefix = "bazel-compile-commands-extractor-cfd16a16cb4c4f27337ef652aa8510dcf1dd01ce",
+        # When you first run this tool, it'll recommend a sha256 hash to put here with a message like: "DEBUG: Rule 'hedron_compile_commands' indicated that a canonical reproducible form can be obtained by modifying arguments sha256 = ..."
+        sha256 = "4c2753a8d446f561391b7968a6d0eed748e8bb0f40adeda51301c57e829c7696",
+    )