[native_toolchain_c] Support environment for cl.exe already set up

pkgs/native_toolchain_c/lib/src/cbuilder/compiler_resolver.dart

@@ -7,6 +7,7 @@ import 'dart:io';
 import 'package:logging/logging.dart';
 import 'package:native_assets_cli/code_assets.dart';
 
+import '../../native_toolchain_c.dart';
 import '../native_toolchain/android_ndk.dart';
 import '../native_toolchain/apple_clang.dart';
 import '../native_toolchain/clang.dart';
@@ -196,29 +197,36 @@ class CompilerResolver {
     return null;
   }
 
-  Future<Uri?> toolchainEnvironmentScript(ToolInstance compiler) async {
-    final fromInput = codeConfig.cCompiler?.envScript;
-    if (fromInput != null) {
-      logger?.fine('Using envScript from input: $fromInput');
-      return fromInput;
+  Future<Map<String, String>> resolveEnvironment(ToolInstance compiler) async {
+    final envScriptFromConfig = codeConfig.cCompiler?.envScript;
+    if (envScriptFromConfig != null) {
+      logger?.fine('Using envScript from input: $envScriptFromConfig');
+      final vcvarsArgs = codeConfig.cCompiler?.envScriptArgs;
+      if (vcvarsArgs != null) {
+        logger?.fine('Using envScriptArgs from input: $vcvarsArgs');
+      }
+      return await environmentFromBatchFile(
+        envScriptFromConfig,
+        arguments: vcvarsArgs ?? [],
+      );
+    }
+
+    if (codeConfig.cCompiler?.compiler != null) {
+      logger?.fine('Compiler provided without envScript,'
+          ' assuming environment is already set up.');
+      return {};
     }
 
     final compilerTool = compiler.tool;
     assert(compilerTool == cl);
     final vcvarsScript =
         (await vcvars(compiler).defaultResolver!.resolve(logger: logger)).first;
-    return vcvarsScript.uri;
-  }
-
-  List<String>? toolchainEnvironmentScriptArguments() {
-    final fromInput = codeConfig.cCompiler?.envScriptArgs;
-    if (fromInput != null) {
-      logger?.fine('Using envScriptArgs from input: $fromInput');
-      return fromInput;
-    }
-
-    // vcvars above already has x64 or x86 in the script name.
-    return null;
+    return await environmentFromBatchFile(
+      vcvarsScript.uri,
+      arguments: [
+        /* vcvarsScript already has x64 or x86 in the script name. */
+      ],
+    );
   }
 
   Future<ToolInstance> resolveLinker() async {

pkgs/native_toolchain_c/lib/src/cbuilder/run_cbuilder.dart

@@ -11,7 +11,6 @@ import '../native_toolchain/msvc.dart';
 import '../native_toolchain/tool_likeness.dart';
 import '../native_toolchain/xcode.dart';
 import '../tool/tool_instance.dart';
-import '../utils/env_from_bat.dart';
 import '../utils/run_process.dart';
 import 'compiler_resolver.dart';
 import 'language.dart';
@@ -334,10 +333,7 @@ class RunCBuilder {
   }
 
   Future<void> runCl({required ToolInstance tool}) async {
-    final vcvars = (await _resolver.toolchainEnvironmentScript(tool))!;
-    final vcvarsArgs = _resolver.toolchainEnvironmentScriptArguments();
-    final environment =
-        await environmentFromBatchFile(vcvars, arguments: vcvarsArgs ?? []);
+    final environment = await _resolver.resolveEnvironment(tool);
 
     final isStaticLib = staticLibrary != null;
     Uri? archiver_;

pkgs/native_toolchain_c/test/cbuilder/compiler_resolver_test.dart

@@ -42,39 +42,47 @@ void main() {
     ].firstOrNull?.uri;
 
     final targetOS = OS.current;
-    final buildInputBuilder = BuildInputBuilder()
-      ..setupShared(
-        packageName: 'dummy',
-        packageRoot: tempUri,
-        outputDirectory: tempUri,
-        outputDirectoryShared: tempUri2,
-      )
-      ..config.setupBuild(
-        linkingEnabled: false,
-        dryRun: false,
-      )
-      ..config.setupShared(buildAssetTypes: [CodeAsset.type])
-      ..config.setupCode(
-        targetOS: targetOS,
-        macOS: targetOS == OS.macOS
-            ? MacOSConfig(targetVersion: defaultMacOSVersion)
-            : null,
-        targetArchitecture: Architecture.current,
-        linkModePreference: LinkModePreference.dynamic,
-        cCompiler: CCompilerConfig(
-          archiver: ar,
-          compiler: cc,
-          linker: ld,
-          envScript: envScript,
-        ),
-      );
-    final buildInput = BuildInput(buildInputBuilder.json);
-    final resolver =
-        CompilerResolver(codeConfig: buildInput.config.code, logger: logger);
-    final compiler = await resolver.resolveCompiler();
-    final archiver = await resolver.resolveArchiver();
-    expect(compiler.uri, buildInput.config.code.cCompiler?.compiler);
-    expect(archiver.uri, buildInput.config.code.cCompiler?.archiver);
+    for (final passInEnvScript in [if (targetOS == OS.windows) true, false]) {
+      final buildInputBuilder = BuildInputBuilder()
+        ..setupShared(
+          packageName: 'dummy',
+          packageRoot: tempUri,
+          outputDirectory: tempUri,
+          outputDirectoryShared: tempUri2,
+        )
+        ..config.setupBuild(
+          linkingEnabled: false,
+          dryRun: false,
+        )
+        ..config.setupShared(buildAssetTypes: [CodeAsset.type])
+        ..config.setupCode(
+          targetOS: targetOS,
+          macOS: targetOS == OS.macOS
+              ? MacOSConfig(targetVersion: defaultMacOSVersion)
+              : null,
+          targetArchitecture: Architecture.current,
+          linkModePreference: LinkModePreference.dynamic,
+          cCompiler: CCompilerConfig(
+            archiver: ar,
+            compiler: cc,
+            linker: ld,
+            envScript: passInEnvScript ? envScript : null,
+          ),
+        );
+      final buildInput = BuildInput(buildInputBuilder.json);
+      final resolver =
+          CompilerResolver(codeConfig: buildInput.config.code, logger: logger);
+      final compiler = await resolver.resolveCompiler();
+      final archiver = await resolver.resolveArchiver();
+      expect(compiler.uri, buildInput.config.code.cCompiler?.compiler);
+      expect(archiver.uri, buildInput.config.code.cCompiler?.archiver);
+      final environment = await resolver.resolveEnvironment(compiler);
+      if (passInEnvScript) {
+        expect(environment, isNot(equals({})));
+      } else {
+        expect(environment, equals({}));
+      }
+    }
   });
 
   test('No compiler found', () async {