bazel: Better remote caching

.bazelrc

@@ -28,7 +28,7 @@ build --copt=-Wno-error=deprecated-declarations
 # Required to stamp our development builds with the current git hash.
 #
 # This script gets run before every build, see the script for more info.
-build --workspace_status_command "python3 misc/bazel/build-info/workspace_status.py"
+build:release-stamp --stamp --workspace_status_command "python3 misc/bazel/build-info/workspace_status.py"
 
 # Output all test output by default, this makes it most like cargo.
 #

Cargo.toml

@@ -333,7 +333,7 @@ store = { path = "misc/cargo-vet" }
 # DO NOT EDIT. Automatically generated by bin/gen-lints.
 [workspace.lints.rust]
 unknown_lints = "allow"
-unexpected_cfgs = { level = "warn", check-cfg = ['cfg(bazel, coverage, nightly_doc_features, release, tokio_unstable)'] }
+unexpected_cfgs = { level = "warn", check-cfg = ['cfg(bazel, stamped, coverage, nightly_doc_features, release, tokio_unstable)'] }
 
 [workspace.lints.rustdoc]
 unportable_markdown = "allow"

misc/bazel/build-info/BUILD.bazel

@@ -38,3 +38,8 @@ gen_build_info(
     rust_file = "build_info.rs",
     visibility = ["//visibility:public"],
 )
+
+config_setting(
+    name = "stamped",
+    values = {"stamp": "true"},
+)

misc/python/materialize/cli/bazel.py

@@ -16,6 +16,10 @@
 
 from materialize import MZ_ROOT, ui
 
+# Path where we put the current revision of the repo that we can side channel
+# into Bazel.
+MZ_GIT_HASH_FILE = "/tmp/mz_git_hash.txt"
+
 
 def main() -> int:
     parser = argparse.ArgumentParser(
@@ -26,6 +30,9 @@ def main() -> int:
 
     (args, sub_args) = parser.parse_known_args()
 
+    # Always update our side-channel git hash incase some command needs it.
+    write_git_hash()
+
     if args.action == "gen":
         gen_cmd(sub_args)
     elif args.action == "fmt":
@@ -147,5 +154,33 @@ def output_path(target) -> pathlib.Path:
     return pathlib.Path(path)
 
 
+def write_git_hash():
+    """
+    Temporary file where we write the current git hash, so we can side channel
+    it into Bazel.
+
+    For production releases we stamp builds with the `workspace_status_command`
+    but this workflow is not friendly to remote caching. Specifically, the
+    "volatile status" of a workspace is not supposed to cause builds to get
+    invalidated, and it doesn't when the result is cached locally, but it does
+    when it's cached remotely.
+
+    See: <https://bazel.build/docs/user-manual#workspace-status>
+         <https://github.com/bazelbuild/bazel/issues/10075>
+    """
+
+    repo = MZ_ROOT / ".git"
+    cmd_args = ["git", f"--git-dir={repo}", "rev-parse", "HEAD"]
+    result = subprocess.run(
+        cmd_args, text=True, stdout=subprocess.PIPE, stderr=subprocess.DEVNULL
+    )
+
+    if result.returncode == 0:
+        with open(MZ_GIT_HASH_FILE, "w") as f:
+            f.write(result.stdout.strip())
+    else:
+        ui.warn(f"Failed to get current revision of {MZ_ROOT}, falling back to all 0s")
+
+
 if __name__ == "__main__":
     main()

misc/python/materialize/cli/gen-lints.py

@@ -178,7 +178,7 @@
 
 EXCLUDE_CRATES = ["workspace-hack"]
 
-CHECK_CFGS = "bazel, coverage, nightly_doc_features, release, tokio_unstable"
+CHECK_CFGS = "bazel, stamped, coverage, nightly_doc_features, release, tokio_unstable"
 
 
 def main() -> None:

misc/wasm/Cargo.toml

@@ -16,7 +16,7 @@ store = { path = "../cargo-vet" }
 # DO NOT EDIT. Automatically generated by bin/gen-lints.
 [workspace.lints.rust]
 unknown_lints = "allow"
-unexpected_cfgs = { level = "warn", check-cfg = ['cfg(bazel, coverage, nightly_doc_features, release, tokio_unstable)'] }
+unexpected_cfgs = { level = "warn", check-cfg = ['cfg(bazel, stamped, coverage, nightly_doc_features, release, tokio_unstable)'] }
 
 [workspace.lints.rustdoc]
 unportable_markdown = "allow"

src/build-info/BUILD.bazel

@@ -22,15 +22,24 @@ rust_library(
         normal = True,
         proc_macro = True,
     ),
-    compile_data = ["@//misc/bazel/build-info:gen_build_info"],
+    compile_data = select({
+        "@//misc/bazel/build-info:stamped": ["@//misc/bazel/build-info:gen_build_info"],
+        "//conditions:default": [],
+    }),
     crate_features = [
         "default",
         "semver",
     ],
     data = [],
     proc_macro_deps = [] + all_crate_deps(proc_macro = True),
-    rustc_env = {"BAZEL_GEN_BUILD_INFO": "$(execpath @//misc/bazel/build-info:gen_build_info)"},
-    rustc_flags = ["--cfg=bazel"],
+    rustc_env = select({
+        "@//misc/bazel/build-info:stamped": {"BAZEL_GEN_BUILD_INFO": "$(execpath @//misc/bazel/build-info:gen_build_info)"},
+        "//conditions:default": {},
+    }),
+    rustc_flags = ["--cfg=bazel"] + select({
+        "@//misc/bazel/build-info:stamped": ["--cfg=stamped"],
+        "//conditions:default": [],
+    }),
     version = "0.0.0",
     deps = [":mz_build_info_build_script"] + all_crate_deps(normal = True),
 )
@@ -57,7 +66,10 @@ rust_test(
         proc_macro_dev = True,
     ),
     rustc_env = {},
-    rustc_flags = ["--cfg=bazel"],
+    rustc_flags = ["--cfg=bazel"] + select({
+        "@//misc/bazel/build-info:stamped": ["--cfg=stamped"],
+        "//conditions:default": [],
+    }),
     version = "0.0.0",
     deps = [] + all_crate_deps(
         normal = True,

src/build-info/Cargo.toml

@@ -20,17 +20,7 @@ default = ["semver", "workspace-hack"]
 [package.metadata.cargo-udeps.ignore]
 normal = ["workspace-hack"]
 
-[package.metadata.cargo-gazelle.lib]
-compile_data = ["@//misc/bazel/build-info:gen_build_info"]
-rustc_flags = ["--cfg=bazel"]
-
-# Skip generating doc tests because there isn't a way to set the rustc flags
-# used for the test, so we can't set the `--cfg=bazel` flag.
-[package.metadata.cargo-gazelle.test.doc]
-skip = true
-
-[package.metadata.cargo-gazelle.lib.rustc_env]
-BAZEL_GEN_BUILD_INFO = "$(execpath @//misc/bazel/build-info:gen_build_info)"
-
-[package.metadata.cargo-gazelle.test.lib]
-rustc_flags = ["--cfg=bazel"]
+# This crate requires some pretty specific configuration, so we manually
+# maintain the BUILD file instead of having cargo-gazelle generate it for us.
+[package.metadata.cargo-gazelle]
+skip_generating = true

src/build-info/src/lib.rs

@@ -90,14 +90,34 @@ macro_rules! build_info {
     };
 }
 
-#[cfg(bazel)]
+#[cfg(all(bazel, stamped))]
 #[macro_export]
 macro_rules! __git_sha_internal {
     () => {
         $crate::private::bazel_variables::GIT_COMMIT_HASH
     };
 }
 
+// To improve the effectiveness of remote caching we only stamp "release" builds
+// and otherwise side-channel git status through a known file.
+//
+// See: <https://github.com/bazelbuild/bazel/issues/10075>
+#[cfg(all(bazel, not(stamped)))]
+#[macro_export]
+macro_rules! __git_sha_internal {
+    () => {
+        $crate::private::run_command_str!(
+            "sh",
+            "-c",
+            r#"if [ -f /tmp/mz_git_hash.txt ]; then
+                    cat /tmp/mz_git_hash.txt
+                else
+                    echo "0000000000000000000000000000000000000000"
+                fi"#
+        )
+    };
+}
+
 #[cfg(not(bazel))]
 #[macro_export]
 macro_rules! __git_sha_internal {
@@ -125,15 +145,6 @@ macro_rules! __git_sha_internal {
     }
 }
 
-#[cfg(bazel)]
-#[macro_export]
-macro_rules! __build_time_internal {
-    () => {
-        $crate::private::bazel_variables::MZ_BUILD_TIME
-    };
-}
-
-#[cfg(not(bazel))]
 #[macro_export]
 macro_rules! __build_time_internal {
     () => {
@@ -148,7 +159,7 @@ pub mod private {
     // Bazel has a "workspace status" feature that allows us to collect info from
     // the workspace (e.g. git hash) at build time. These values get incleded via
     // a generated file.
-    #[cfg(bazel)]
+    #[cfg(all(bazel, stamped))]
     #[allow(unused)]
     pub mod bazel_variables {
         include!(std::env!("BAZEL_GEN_BUILD_INFO"));