[buildbuddy 1/6]: allow tool override

This change is needed because BuildBuddy cache and execution views key
off the Bazel RequestMetadata tool name. Buck2 reports buck2 by default,
so BuildBuddy-backed Buck2 requests need an override when a deployment
requires Bazel-compatible request metadata.

Add a buck2_re_client.request_metadata_tool_name option that defaults to
buck2 and thread it through OSS RE gRPC requests. A later BuildBuddy
profile commit uses the option to send bazel.

Author: sluongng

app/buck2_common/src/legacy_configs/dice.rs

@@ -463,6 +463,10 @@ const CONFIGS_INVISIBLE_TO_DICE: &[BuckconfigKeyRef<'static>] = &[
         section: "buck2_re_client",
         property: "override_use_case",
     },
+    BuckconfigKeyRef {
+        section: "buck2_re_client",
+        property: "request_metadata_tool_name",
+    },
     BuckconfigKeyRef {
         section: "scuba",
         property: "defaults",

app/buck2_re_configuration/src/lib.rs

@@ -466,6 +466,8 @@ pub struct Buck2OssReConfiguration {
     pub instance_name: Option<String>,
     /// Use the Meta version of the request metadata
     pub use_fbcode_metadata: bool,
+    /// Optional override for RequestMetadata.tool_details.tool_name.
+    pub request_metadata_tool_name: Option<String>,
     /// The max size for a GRPC message to be decoded.
     pub max_decoding_message_size: Option<usize>,
     /// The max cumulative blob size for batch CAS methods.
@@ -593,6 +595,10 @@ impl Buck2OssReConfiguration {
                     property: "use_fbcode_metadata",
                 })?
                 .unwrap_or(false),
+            request_metadata_tool_name: legacy_config.parse(BuckconfigKeyRef {
+                section: BUCK2_RE_CLIENT_CFG_SECTION,
+                property: "request_metadata_tool_name",
+            })?,
             max_decoding_message_size: legacy_config.parse(BuckconfigKeyRef {
                 section: BUCK2_RE_CLIENT_CFG_SECTION,
                 property: "max_decoding_message_size",
@@ -701,4 +707,28 @@ mod tests {
         assert_eq!(config.remote_cache_compression_threshold, Some(100));
         Ok(())
     }
+
+    #[test]
+    fn oss_config_parses_request_metadata_tool_name() -> buck2_error::Result<()> {
+        let legacy_config = parse(
+            &[(
+                "config",
+                "[buck2_re_client]\nrequest_metadata_tool_name = bazel\n",
+            )],
+            "config",
+        )?;
+        let config = Buck2OssReConfiguration::from_legacy_config(&legacy_config, Vec::new())?;
+
+        assert_eq!(config.request_metadata_tool_name.as_deref(), Some("bazel"));
+        Ok(())
+    }
+
+    #[test]
+    fn oss_config_leaves_request_metadata_tool_name_unset_by_default() -> buck2_error::Result<()> {
+        let legacy_config = parse(&[("config", "")], "config")?;
+        let config = Buck2OssReConfiguration::from_legacy_config(&legacy_config, Vec::new())?;
+
+        assert_eq!(config.request_metadata_tool_name, None);
+        Ok(())
+    }
 }

docs/users/remote_execution.md

@@ -42,6 +42,9 @@ Keys supported include:
   interpolation syntax ($VAR). They will be substituted before reading the file.
 - `instance_name` - an instance name to pass on execution, action cache, and CAS
   requests.
+- `request_metadata_tool_name` - optional override for
+  `RequestMetadata.tool_details.tool_name` in the Bazel remote execution request
+  metadata. This defaults to `buck2`.
 - `capabilities` - whether Buck2 should query the RE capabilities service. This
   defaults to enabled.
 - `max_total_batch_size` - optional client-side cap for cumulative blob size in