change tuple indexing

.bazelrc

@@ -108,6 +108,11 @@ build --action_env=LANG=en_US.UTF-8
 build --enable_platform_specific_config
 build:linux --define=pfm=1
 
+# Enable TCMalloc on Linux as well.
+# TODO: tcmalloc needs to support compiler-explorer; see:
+# https://github.com/carbon-language/carbon-lang/issues/4176
+# build:linux --custom_malloc=@tcmalloc//tcmalloc
+
 # Allow users to override any of the flags desired by importing a user-specific
 # RC file here if present.
 try-import %workspace%/user.bazelrc

.clangd

@@ -0,0 +1,7 @@
+# Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+# Exceptions. See /LICENSE for license information.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+CompileFlags:
+  # Workaround for https://github.com/clangd/clangd/issues/1582
+  Remove: [-march=*]

MODULE.bazel

@@ -4,14 +4,33 @@
 
 """Bazel modules.
 
-If `MODULE.bazel.lock` changes locally, it means the host platform hasn't yet
-been added to the lock file. Running `bazel mod deps` provides a canonical
-update to `MODULE.bazel.lock`; create a PR with those changes in order to
-include the host platform.
-
-Platforms tested with GitHub actions are kept up-to-date. Other platforms may
-fall out of sync on dependency changes, and should be updated with a PR the same
-way a platform is added.
+`MODULE.bazel.lock` may change locally when `bazel` is exexcuted. This means one
+of:
+
+1.  `MODULE.bazel` is changing.
+    -   Running `bazel mod deps` provides a canonical update to
+        `MODULE.bazel.lock`; include the changes.
+    -   GitHub test actions may also identify platform-specific lockfile
+        updates.
+2.  The `bazel` version doesn't match the version used to generate the
+    `MODULE.bazel.lock`.
+    -   Bazel releases can change the lock file contents.
+    -   We use Bazelisk in order to keep everyone using the same version:
+        https://bazel.build/install/bazelisk
+        -   Developers are encouraged to alias `bazel` to `bazelisk` for
+            ease-of-use; some setups, like Homebrew, will include that with a
+            `bazelisk` install.
+        -   Contribution tools documentation includes `bazelisk` setup:
+            https://github.com/carbon-language/carbon-lang/blob/trunk/docs/project/contribution_tools.md
+    -   Make sure `bazelisk --version` (or `bazel --version`) matches the
+        version in `.bazeliskrc`.
+3.  The host platform hasn't yet been added to the lock file.
+    -   Platforms tested with GitHub actions are kept up-to-date. Other
+        platforms may fall out of sync due to `bazel` or dependency changes,
+        and should be updated with a PR the same way a platform is added.
+    -   Running `bazel mod deps` provides a canonical update to
+        `MODULE.bazel.lock`; create a PR with those changes in order to include
+        the host platform.
 """
 
 module(name = "carbon")
@@ -43,6 +62,17 @@ archive_override(
     urls = ["https://sourceforge.net/projects/perfmon2/files/libpfm4/libpfm-{0}.tar.gz".format(libpfm_version)],
 )
 
+# The registry has a snapshot, but upstream is active and not regularly marking
+# releases. We start with the BCR snapshot to avoid a miss and then override it
+# with a more recent commit.
+bazel_dep(name = "tcmalloc", version = "0.0.0-20240411-5ed309d", dev_dependency = True)
+git_override(
+    module_name = "tcmalloc",
+    # HEAD as of 2024-07-14.
+    commit = "923df94c922e0cd2d0512c1662d374f63c2c0c96",
+    remote = "https://github.com/google/tcmalloc.git",
+)
+
 bazel_dep(name = "rules_bison", version = "0.2.2")
 bazel_dep(name = "rules_flex", version = "0.2.1")
 bazel_dep(name = "rules_m4", version = "0.2.3")