Allow environment overriding of C Compiler Config

Author: mkustermann

pkgs/native_assets_cli/lib/src/model/hook_config.dart

@@ -411,15 +411,57 @@ abstract class HookConfigImpl implements HookConfig {
 
     final cCompilerJson =
         config.getOptional<Map<String, Object?>>(CCompilerConfigImpl.configKey);
-    if (cCompilerJson == null) return CCompilerConfigImpl();
 
-    final compiler = _parseCompiler(baseUri, cCompilerJson);
+    Uri? archiver;
+    Uri? compiler;
+    Uri? linker;
+    Uri? envScript;
+    List<String>? envScriptArgs;
+    if (cCompilerJson != null) {
+      compiler = _parseCompiler(baseUri, cCompilerJson);
+      archiver = _parseArchiver(baseUri, cCompilerJson);
+      envScript = _parseEnvScript(baseUri, cCompilerJson, compiler);
+      envScriptArgs = _parseEnvScriptArgs(cCompilerJson);
+      linker = _parseLinker(baseUri, cCompilerJson);
+    }
+
+    // If the bundling tool didn't specify a C compiler we fallback to
+    // identifying the C compiler based on specific environment variables.
+    {
+      final env = Platform.environment;
+      String? unparseKey(String key) => key.replaceAll('.', '__').toUpperCase();
+      String? lookup(String key) => env[unparseKey(key)];
+      Uri? lookupUri(String key) {
+        final value = lookup(key);
+        return value != null ? Uri.file(value) : null;
+      }
+
+      List<String>? lookupList(String key) {
+        final value = lookup(key);
+        if (value == null) return null;
+        final list = value
+            .split(' ')
+            .map((arg) => arg.trim())
+            .where((arg) => arg.isNotEmpty)
+            .toList();
+        if (list.isEmpty) return null;
+        return list;
+      }
+
+      archiver ??= lookupUri(CCompilerConfigImpl.arConfigKeyFull);
+      compiler ??= lookupUri(CCompilerConfigImpl.ccConfigKeyFull);
+      linker ??= lookupUri(CCompilerConfigImpl.ldConfigKeyFull);
+      envScript ??= lookupUri(CCompilerConfigImpl.envScriptConfigKeyFull);
+      envScriptArgs ??=
+          lookupList(CCompilerConfigImpl.envScriptArgsConfigKeyFull);
+    }
+
     return CCompilerConfigImpl(
-      archiver: _parseArchiver(baseUri, cCompilerJson),
+      archiver: archiver,
       compiler: compiler,
-      envScript: _parseEnvScript(baseUri, cCompilerJson, compiler),
-      envScriptArgs: _parseEnvScriptArgs(cCompilerJson),
-      linker: _parseLinker(baseUri, cCompilerJson),
+      envScript: envScript,
+      envScriptArgs: envScriptArgs,
+      linker: linker,
     );
   }