chore: add supported configurations

The configuration macro is changed to a registry that includes types
and default values next to the configuration names.

This is used for compile time generation instead of using runtime
checks for the configurations (environment variables).

For safety, failing to parse configurations is now going to log a
warning instead. This aligns with other platforms / tracers to not
crash a customer in production where their staging configuration
might be valid and their production one not.

The macro must now be used for any new configuration added and a CI
job verifies that all entries do exist. If a new env is added
otherwise it should fail.

The CI will also verify that the generated file is up to date and
matches the remote registry. It would fail, if either is not the
case.

The behavior change is documented in the README.md.

Author: BridgeAR

.github/workflows/dev.yml

@@ -12,6 +12,19 @@ jobs:
         run: bin/check-format
       - name: Shellcheck
         run: find bin/ -executable -type f -print0 | xargs -0 shellcheck
+      - name: Verify environment variable allowlist
+        run: bin/check-environment-variables
+      - name: Verify supported configurations metadata
+        run: |
+          tmp_dir="$(mktemp -d)"
+          trap 'rm -rf "$tmp_dir"' EXIT
+          cp metadata/supported-configurations.json "$tmp_dir/supported-configurations.json"
+          bin/generate-supported-configurations
+          if ! diff -q "$tmp_dir/supported-configurations.json" metadata/supported-configurations.json >/dev/null 2>&1; then
+            echo "ERROR: metadata/supported-configurations.json got out of sync with implemented configurations. Please run bin/generate-supported-configurations locally."
+            diff -u "$tmp_dir/supported-configurations.json" metadata/supported-configurations.json || true
+            exit 1
+          fi
 
   build-linux-cmake:
     strategy:

.gitignore

@@ -11,4 +11,5 @@ MODULE.bazel.lock
 .vscode
 .cache/
 .cursor/
-.DS_Store
+.DS_Store
+bin/.supported-configurations

bin/README.md

@@ -1,5 +1,6 @@
 Scripts
 =======
+
 This directory contains scripts that are useful during development.
 
 - [bazel-build](bazel-build) builds the library using [Bazel][1] via [bazelisk][2].
@@ -8,6 +9,12 @@ This directory contains scripts that are useful during development.
 - [check](check) performs some of the checks that [continuous
   integration](../.circleci) performs. It's convenient to run this script before
   pushing changes.
+- [check-environment-variables](check-environment-variables) validates that
+  all `DD_`/`OTEL_` environment variables used by the codebase are allowlisted
+  in
+  [include/datadog/environment_registry.h](../include/datadog/environment_registry.h)
+  (the source of truth used by
+  [include/datadog/environment.h](../include/datadog/environment.h)).
 - [check-format](check-format) verifies that the source code is formatted as
   [format](format) prefers.
 - [check-version](check-version) accepts a version string as a command line
@@ -16,6 +23,15 @@ This directory contains scripts that are useful during development.
 - [cmake-build](cmake-build) builds the library using [CMake][3].
 - [format](format) formats all of the C++ source code using
   [clang-format-14][4].
+- [generate-supported-configurations](generate-supported-configurations)
+  regenerates
+  [metadata/supported-configurations.json](../metadata/supported-configurations.json)
+  from
+  [include/datadog/environment_registry.h](../include/datadog/environment_registry.h).
+  This script (and [check-environment-variables](check-environment-variables))
+  compiles and executes
+  [supported-configurations.cpp](supported-configurations.cpp) via
+  [supported-configurations](supported-configurations).
 - [hasher-example](hasher-example) builds the library, including the [command
   line example](../examples/hasher) program, and then runs the example.
 - [http-server-example](http-server-example) runs the docker compose based [HTTP

bin/check-environment-variables

@@ -0,0 +1,6 @@
+#!/bin/sh
+
+set -eu
+
+SCRIPT_DIR=$(cd "$(dirname "$0")" && pwd)
+exec "$SCRIPT_DIR/supported-configurations" check

bin/generate-supported-configurations

@@ -0,0 +1,6 @@
+#!/bin/sh
+
+set -eu
+
+SCRIPT_DIR=$(cd "$(dirname "$0")" && pwd)
+exec "$SCRIPT_DIR/supported-configurations" generate

bin/supported-configurations

@@ -0,0 +1,21 @@
+#!/bin/sh
+
+set -eu
+
+SCRIPT_DIR=$(cd "$(dirname "$0")" && pwd)
+REPO_ROOT=$(cd "$SCRIPT_DIR/.." && pwd)
+SOURCE="$SCRIPT_DIR/supported-configurations.cpp"
+BINARY="$SCRIPT_DIR/.supported-configurations"
+
+compiler=${CXX:-c++}
+
+if [ ! -x "$BINARY" ] || [ "$SOURCE" -nt "$BINARY" ]; then
+  # `CXX` may contain wrappers/flags (e.g. "ccache c++").
+  (
+    # shellcheck disable=SC2086
+    set -- $compiler
+    "$@" -std=c++17 -O2 -I"$REPO_ROOT/src/datadog" "$SOURCE" -o "$BINARY"
+  )
+fi
+
+exec "$BINARY" "$@"