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[web] --web-define flag not working with flutter build web (works with flutter run) on flutter 3.41.0-0.2.pre #182076

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#182079
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[web] --web-define flag not working with flutter build web (works with flutter run) on flutter 3.41.0-0.2.pre#182076
#182079
Labels
has reproducible stepsThe issue has been confirmed reproducible and is ready to work onplatform-webWeb applications specificallytoolAffects the "flutter" command-line tool. See also t: labels.
@mkucharski17

Description

@mkucharski17
mkucharski17
opened on Feb 9, 2026

Steps to reproduce

  1. Create a Flutter web project: flutter create bug_repro
  2. Add a {{VERSION}} placeholder to web/index.html: 
    <script>
  {{flutter_js}}
  {{flutter_build_config}}
  
  // Append version query parameter to main.dart.js URL for cache invalidation
  // The {{VERSION}} placeholder should be replaced by --web-define=VERSION=...
  _flutter.buildConfig.builds[0].mainJsPath = "main.dart.js?v={{VERSION}}";
  
  _flutter.loader.load({
    onEntrypointLoaded: async function (engineInitializer) {
      const appRunner = await engineInitializer.initializeEngine();
      await appRunner.runApp();
    },
  });
</script>
  3. Run flutter build web --web-define=VERSION=1.0.0

Expected results

  • Build succeeds without errors
  • The {{VERSION}} placeholder is replaced with 1.0.0 in the output build/web/index.html
  • The generated file contains: main.dart.js?v=1.0.0
  • Verification: grep "mainJsPath" build/web/index.html shows main.dart.js?v=1.0.0

Actual results

Build fails with error:

Target web_templated_files failed: Error: Missing web-define variable: VERSION

Please provide the missing variable using:
flutter run --web-define=VERSION=VALUE
or
flutter build web --web-define=VERSION=VALUE

Code sample

Code sample 
<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <title>Bug Reproduction</title>
</head>
<body>
  <script>
    {{flutter_js}}
    {{flutter_build_config}}
    
    // This {{VERSION}} placeholder should be replaced by --web-define=VERSION=...
    _flutter.buildConfig.builds[0].mainJsPath = "main.dart.js?v={{VERSION}}";
    
    _flutter.loader.load({
      onEntrypointLoaded: async function (engineInitializer) {
        const appRunner = await engineInitializer.initializeEngine();
        await appRunner.runApp();
      },
    });
  </script>
</body>
</html>

Logs

Logs 
[  +16 ms] executing: sysctl hw.optional.arm64
[   +3 ms] Exit code 0 from: sysctl hw.optional.arm64
[        ] hw.optional.arm64: 1
[   +4 ms] Artifact Instance of 'MaterialFonts' is not required, skipping update.
[        ] Artifact Instance of 'GradleWrapper' is not required, skipping update.
[        ] Artifact Instance of 'AndroidGenSnapshotArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'AndroidInternalBuildArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'IOSEngineArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'FlutterWebSdk' is not required, skipping update.
[        ] Artifact Instance of 'LegacyCanvasKitRemover' is not required, skipping update.
[        ] Artifact Instance of 'FlutterSdk' is not required, skipping update.
[        ] Artifact Instance of 'WindowsEngineArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'MacOSEngineArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'LinuxEngineArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'LinuxFuchsiaSDKArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'MacOSFuchsiaSDKArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'FlutterRunnerSDKArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'FlutterRunnerDebugSymbols' is not required, skipping update.
[        ] Artifact Instance of 'IosUsbArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'IosUsbArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'IosUsbArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'IosUsbArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'IosUsbArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'IosUsbArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'FontSubsetArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'PubDependencies' is not required, skipping update.
[        ] executing: [/Users/michalkucharski/fvm/versions/3.41.0-0.2.pre/] git -c log.showSignature=false log HEAD -n 1 --pretty=format:%ad
--date=iso
[  +16 ms] Exit code 0 from: git -c log.showSignature=false log HEAD -n 1 --pretty=format:%ad --date=iso
[        ] 2026-01-28 11:28:23 -0800
[  +12 ms] Artifact Instance of 'AndroidGenSnapshotArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'AndroidInternalBuildArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'IOSEngineArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'FlutterWebSdk' is not required, skipping update.
[        ] Artifact Instance of 'FlutterEngineStamp' is not required, skipping update.
[        ] Artifact Instance of 'LegacyCanvasKitRemover' is not required, skipping update.
[        ] Artifact Instance of 'WindowsEngineArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'MacOSEngineArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'LinuxEngineArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'LinuxFuchsiaSDKArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'MacOSFuchsiaSDKArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'FlutterRunnerSDKArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'FlutterRunnerDebugSymbols' is not required, skipping update.
[  +18 ms] Artifact Instance of 'MaterialFonts' is not required, skipping update.
[        ] Artifact Instance of 'GradleWrapper' is not required, skipping update.
[        ] Artifact Instance of 'AndroidGenSnapshotArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'AndroidInternalBuildArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'IOSEngineArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'FlutterEngineStamp' is not required, skipping update.
[        ] Artifact Instance of 'FlutterSdk' is not required, skipping update.
[        ] Artifact Instance of 'WindowsEngineArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'MacOSEngineArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'LinuxEngineArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'LinuxFuchsiaSDKArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'MacOSFuchsiaSDKArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'FlutterRunnerSDKArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'FlutterRunnerDebugSymbols' is not required, skipping update.
[        ] Artifact Instance of 'IosUsbArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'IosUsbArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'IosUsbArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'IosUsbArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'IosUsbArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'IosUsbArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'FontSubsetArtifacts' is not required, skipping update.
[   +7 ms] Artifact Instance of 'PubDependencies' is not required, skipping update.
[   +7 ms] executing: [/Users/michalkucharski/Desktop/flutter_web_define_reproduction/]
/Users/michalkucharski/fvm/versions/3.41.0-0.2.pre/bin/cache/dart-sdk/bin/dart pub --suppress-analytics --color --directory . get --example
Resolving dependencies... 
Downloading packages... 
  meta 1.17.0 (1.18.1 available)
  test_api 0.7.8 (0.7.9 available)
Got dependencies!
2 packages have newer versions incompatible with dependency constraints.
Try `flutter pub outdated` for more information.
[  +97 ms] Skipping generating web_plugin_registrant.dart because it is up-to-date.
[  +42 ms] generated_plugin_registrant.dart not found. Skipping.
[        ] Compiling lib/main.dart for the Web...
[   +2 ms] Initializing file store
[   +1 ms] Done initializing file store
[  +18 ms] Skipping target: web_entrypoint
[        ] invalidated build due to missing files: /Users/michalkucharski/Desktop/flutter_web_define_reproduction/web/*/index.html,
/Users/michalkucharski/Desktop/flutter_web_define_reproduction/web/flutter_bootstrap.js
[        ] Skipping target: dart_build
[        ] Skipping target: gen_localizations
[        ] web_templated_files: Starting due to {InvalidatedReasonKind.buildKeyChanged: The target build key changed.,
InvalidatedReasonKind.outputSetAddition: The following outputs were added to the output set:
/Users/michalkucharski/Desktop/flutter_web_define_reproduction/build/web/*/index.html,/Users/michalkucharski/Desktop/flutter_web_define_reprodu
ction/build/web/flutter_bootstrap.js, InvalidatedReasonKind.inputMissing: The following inputs were missing:
/Users/michalkucharski/Desktop/flutter_web_define_reproduction/web/*/index.html,/Users/michalkucharski/Desktop/flutter_web_define_reproduction/
web/flutter_bootstrap.js}
[        ] web_static_assets: Starting due to {InvalidatedReasonKind.outputMissing: The following outputs were missing:
/Users/michalkucharski/Desktop/flutter_web_define_reproduction/.dart_tool/flutter_build/825161eebb3468bc1b39a75b1eaba464/flutter.js,/Users/mich
alkucharski/Desktop/flutter_web_define_reproduction/.dart_tool/flutter_build/825161eebb3468bc1b39a75b1eaba464/canvaskit/wimp.wasm,/Users/michal
kucharski/Desktop/flutter_web_define_reproduction/.dart_tool/flutter_build/825161eebb3468bc1b39a75b1eaba464/canvaskit/skwasm.js,/Users/michalku
charski/Desktop/flutter_web_define_reproduction/.dart_tool/flutter_build/825161eebb3468bc1b39a75b1eaba464/canvaskit/skwasm_heavy.js,/Users/mich
alkucharski/Desktop/flutter_web_define_reproduction/.dart_tool/flutter_build/825161eebb3468bc1b39a75b1eaba464/canvaskit/skwasm.js.symbols,/User
s/michalkucharski/Desktop/flutter_web_define_reproduction/.dart_tool/flutter_build/825161eebb3468bc1b39a75b1eaba464/canvaskit/canvaskit.js.symb
ols,/Users/michalkucharski/Desktop/flutter_web_define_reproduction/.dart_tool/flutter_build/825161eebb3468bc1b39a75b1eaba464/canvaskit/skwasm_h
eavy.js.symbols,/Users/michalkucharski/Desktop/flutter_web_define_reproduction/.dart_tool/flutter_build/825161eebb3468bc1b39a75b1eaba464/canvas
kit/skwasm.wasm,/Users/michalkucharski/Desktop/flutter_web_define_reproduction/.dart_tool/flutter_build/825161eebb3468bc1b39a75b1eaba464/canvas
kit/chromium/canvaskit.js.symbols,/Users/michalkucharski/Desktop/flutter_web_define_reproduction/.dart_tool/flutter_build/825161eebb3468bc1b39a
75b1eaba464/canvaskit/chromium/canvaskit.js,/Users/michalkucharski/Desktop/flutter_web_define_reproduction/.dart_tool/flutter_build/825161eebb3
468bc1b39a75b1eaba464/canvaskit/chromium/canvaskit.wasm,/Users/michalkucharski/Desktop/flutter_web_define_reproduction/.dart_tool/flutter_build
/825161eebb3468bc1b39a75b1eaba464/canvaskit/canvaskit.js,/Users/michalkucharski/Desktop/flutter_web_define_reproduction/.dart_tool/flutter_buil
d/825161eebb3468bc1b39a75b1eaba464/canvaskit/wimp.js,/Users/michalkucharski/Desktop/flutter_web_define_reproduction/.dart_tool/flutter_build/82
5161eebb3468bc1b39a75b1eaba464/canvaskit/canvaskit.wasm,/Users/michalkucharski/Desktop/flutter_web_define_reproduction/.dart_tool/flutter_build
/825161eebb3468bc1b39a75b1eaba464/canvaskit/wimp.js.symbols,/Users/michalkucharski/Desktop/flutter_web_define_reproduction/.dart_tool/flutter_b
uild/825161eebb3468bc1b39a75b1eaba464/canvaskit/skwasm_heavy.wasm}
[ +317 ms] Skipping target: dart2js
[   +1 ms] web_static_assets: Complete
[   +1 ms] dart2wasm: Starting due to {}
[   +4 ms] executing: /Users/michalkucharski/fvm/versions/3.41.0-0.2.pre/bin/cache/dart-sdk/bin/dart compile wasm
--packages=/Users/michalkucharski/Desktop/flutter_web_define_reproduction/.dart_tool/package_config.json
--extra-compiler-option=--platform=/Users/michalkucharski/fvm/versions/3.41.0-0.2.pre/bin/cache/flutter_web_sdk/kernel/dart2wasm_platform.dill
-Ddart.vm.profile=false -Ddart.vm.product=true --extra-compiler-option=--delete-tostring-package-uri=dart:ui
--extra-compiler-option=--delete-tostring-package-uri=package:flutter --extra-compiler-option=--import-shared-memory
--extra-compiler-option=--shared-memory-max-pages=32768 -DFLUTTER_VERSION=3.41.0-0.2.pre -DFLUTTER_CHANNEL=beta
-DFLUTTER_GIT_URL=https://github.com/flutter/flutter.git -DFLUTTER_FRAMEWORK_REVISION=a7c4c6bf74 -DFLUTTER_ENGINE_REVISION=15d137647e
-DFLUTTER_DART_VERSION=3.11.0 (build 3.11.0-296.4.beta) -DFLUTTER_WEB_USE_SKIA=false -DFLUTTER_WEB_USE_SKWASM=true
-DFLUTTER_WEB_CANVASKIT_URL=https://www.gstatic.com/flutter-canvaskit/15d137647e372c59e8dcb78f670ab7686a0d1031/
--extra-compiler-option=--depfile=/Users/michalkucharski/Desktop/flutter_web_define_reproduction/.dart_tool/flutter_build/825161eebb3468bc1b39a
75b1eaba464/dart2wasm.d -O2 --strip-wasm --no-source-maps --minify --extra-compiler-option=--dry-run -o
/Users/michalkucharski/Desktop/flutter_web_define_reproduction/.dart_tool/flutter_build/825161eebb3468bc1b39a75b1eaba464/main.dart.wasm
/Users/michalkucharski/Desktop/flutter_web_define_reproduction/.dart_tool/flutter_build/825161eebb3468bc1b39a75b1eaba464/main.dart
[+12424 ms] Wasm dry run succeeded. Consider building and testing your application with the `--wasm` flag. See docs for more info:
                     https://docs.flutter.dev/platform-integration/web/wasm
[   +1 ms] Use --no-wasm-dry-run to disable these warnings.
[  +14 ms] dart2wasm: Complete
[   +6 ms] Persisting file store
[   +6 ms] Done persisting file store
[   +5 ms] Target web_templated_files failed: Error: Missing web-define variable: VERSION
           
           Please provide the missing variable using:
           flutter run --web-define=VERSION=VALUE
           or
           flutter build web --web-define=VERSION=VALUE
           #0      throwToolExit (package:flutter_tools/src/base/common.dart:34:3)
           #1      WebTemplate._applyVariableSubstitutions (package:flutter_tools/src/web_template.dart:191:5)
           #2      WebTemplate.withSubstitutions (package:flutter_tools/src/web_template.dart:136:18)
           #3      WebTemplatedFiles.build (package:flutter_tools/src/build_system/targets/web.dart:756:59)
           <asynchronous suspension>
           #4      _BuildInstance._invokeInternal (package:flutter_tools/src/build_system/build_system.dart:937:9)
           <asynchronous suspension>
           #5      Future.wait.<anonymous closure> (dart:async/future.dart:546:21)
           <asynchronous suspension>
           #6      _BuildInstance.invokeTarget (package:flutter_tools/src/build_system/build_system.dart:875:32)
           <asynchronous suspension>
           #7      Future.wait.<anonymous closure> (dart:async/future.dart:546:21)
           <asynchronous suspension>
           #8      _BuildInstance.invokeTarget (package:flutter_tools/src/build_system/build_system.dart:875:32)
           <asynchronous suspension>
           #9      FlutterBuildSystem.build (package:flutter_tools/src/build_system/build_system.dart:684:16)
           <asynchronous suspension>
           #10     WebBuilder.buildWeb (package:flutter_tools/src/web/compile.dart:101:34)
           <asynchronous suspension>
           #11     BuildWebCommand.runCommand (package:flutter_tools/src/commands/build_web.dart:299:5)
           <asynchronous suspension>
           #12     FlutterCommand.run.<anonymous closure> (package:flutter_tools/src/runner/flutter_command.dart:1590:27)
           <asynchronous suspension>
           #13     AppContext.run.<anonymous closure> (package:flutter_tools/src/base/context.dart:154:19)
           <asynchronous suspension>
           #14     CommandRunner.runCommand (package:args/command_runner.dart:212:13)
           <asynchronous suspension>
           #15     FlutterCommandRunner.runCommand.<anonymous closure> (package:flutter_tools/src/runner/flutter_command_runner.dart:496:9)
           <asynchronous suspension>
           #16     AppContext.run.<anonymous closure> (package:flutter_tools/src/base/context.dart:154:19)
           <asynchronous suspension>
           #17     FlutterCommandRunner.runCommand (package:flutter_tools/src/runner/flutter_command_runner.dart:431:5)
           <asynchronous suspension>
           #18     FlutterCommandRunner.run.<anonymous closure> (package:flutter_tools/src/runner/flutter_command_runner.dart:307:33)
           <asynchronous suspension>
           #19     run.<anonymous closure>.<anonymous closure> (package:flutter_tools/runner.dart:104:11)
           <asynchronous suspension>
           #20     AppContext.run.<anonymous closure> (package:flutter_tools/src/base/context.dart:154:19)
           <asynchronous suspension>
           #21     main (package:flutter_tools/executable.dart:103:3)
           <asynchronous suspension>


[   +1 ms] Compiling lib/main.dart for the Web... (completed in 12.8s)
[        ] "flutter web" took 12,993ms.
[   +3 ms] executing: sw_vers -productName
[   +9 ms] Exit code 0 from: sw_vers -productName
[        ] macOS
[        ] executing: sw_vers -productVersion
[   +7 ms] Exit code 0 from: sw_vers -productVersion
[        ] 14.6
[        ] executing: sw_vers -buildVersion
[   +7 ms] Exit code 0 from: sw_vers -buildVersion
[        ] 23G80
[        ] executing: uname -m
[   +2 ms] Exit code 0 from: uname -m
[        ] arm64
[  +24 ms] Error: Failed to compile application for the Web.
[        ] 
           #0      throwToolExit (package:flutter_tools/src/base/common.dart:34:3)
           #1      WebBuilder.buildWeb (package:flutter_tools/src/web/compile.dart:145:7)
           <asynchronous suspension>
           #2      BuildWebCommand.runCommand (package:flutter_tools/src/commands/build_web.dart:299:5)
           <asynchronous suspension>
           #3      FlutterCommand.run.<anonymous closure> (package:flutter_tools/src/runner/flutter_command.dart:1590:27)
           <asynchronous suspension>
           #4      AppContext.run.<anonymous closure> (package:flutter_tools/src/base/context.dart:154:19)
           <asynchronous suspension>
           #5      CommandRunner.runCommand (package:args/command_runner.dart:212:13)
           <asynchronous suspension>
           #6      FlutterCommandRunner.runCommand.<anonymous closure> (package:flutter_tools/src/runner/flutter_command_runner.dart:496:9)
           <asynchronous suspension>
           #7      AppContext.run.<anonymous closure> (package:flutter_tools/src/base/context.dart:154:19)
           <asynchronous suspension>
           #8      FlutterCommandRunner.runCommand (package:flutter_tools/src/runner/flutter_command_runner.dart:431:5)
           <asynchronous suspension>
           #9      FlutterCommandRunner.run.<anonymous closure> (package:flutter_tools/src/runner/flutter_command_runner.dart:307:33)
           <asynchronous suspension>
           #10     run.<anonymous closure>.<anonymous closure> (package:flutter_tools/runner.dart:104:11)
           <asynchronous suspension>
           #11     AppContext.run.<anonymous closure> (package:flutter_tools/src/base/context.dart:154:19)
           <asynchronous suspension>
           #12     main (package:flutter_tools/executable.dart:103:3)
           <asynchronous suspension>
           
           
[        ] Running 1 shutdown hook
[        ] Shutdown hooks complete
[  +63 ms] exiting with code 1

Flutter Doctor output

Doctor output 
$ flutter doctor -v

[✓] Flutter (Channel beta, 3.41.0-0.2.pre, on macOS 14.6 23G80 darwin-arm64, locale en-PL)
    • Flutter version 3.41.0-0.2.pre on channel beta at /Users/michalkucharski/fvm/versions/3.41.0-0.2.pre
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision a7c4c6bf74 (12 days ago), 2026-01-28 11:28:23 -0800
    • Engine revision 15d137647e
    • Dart version 3.11.0 (build 3.11.0-296.4.beta)
    • DevTools version 2.54.1
    • Feature flags: enable-web, enable-linux-desktop, enable-macos-desktop, enable-windows-desktop, enable-android, enable-ios, cli-animations, enable-native-assets, omit-legacy-version-file, enable-lldb-debugging, enable-uiscene-migration

[✓] Chrome - develop for the web
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

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    has reproducible stepsThe issue has been confirmed reproducible and is ready to work onplatform-webWeb applications specificallytoolAffects the "flutter" command-line tool. See also t: labels.

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