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2026-09-23-web-image-flutter-from-fvmrc

title: The web image installs the Flutter your .fvmrc names affects: dartway_cli: "0.11.1"​

Who is affected​

A project whose <project>_flutter/Dockerfile builds FROM ghcr.io/cirruslabs/flutter:<version> while its .fvmrc pins another version — every project created before dartway_cli 0.11.1 that moves its .fvmrc past 3.44.0, the last image published. Flutter pins some of the packages an app resolves, so the lock your Flutter writes is refused by the image's flutter pub get --enforce-lockfile, inside docker build, with a list of changed packages. dart run dartway_cli:dartway deploy check names the mismatch first (web-flutter-version, an error).

A project whose image tag and .fvmrc agree has nothing to do until it moves its Flutter.

What to change​

<project>_flutter/Dockerfile, the first line of the build stage:

- FROM ghcr.io/cirruslabs/flutter:3.44.0 AS build
+ FROM debian:bookworm-slim AS build
+
+ RUN apt-get update \
+  && apt-get install -y --no-install-recommends ca-certificates curl git unzip xz-utils \
+  && rm -rf /var/lib/apt/lists/*
+ COPY <project>_flutter/.fvmrc /tmp/fvmrc
+ RUN version="$(sed -n 's/.*"flutter"[^"]*"\([^"]*\)".*/\1/p' /tmp/fvmrc)" \
+  && test -n "$version" \
+  && git clone --quiet --depth 1 --branch "$version" \
+       https://github.com/flutter/flutter.git /opt/flutter
+ ENV PATH="/opt/flutter/bin:$PATH"
+ RUN flutter --disable-analytics && flutter precache --web

The rest of the stage is unchanged. The first build on a server takes a few minutes longer; the Flutter layer is cached until .fvmrc changes.

How to check​

dart run dartway_cli:dartway deploy check --env <environment> --local: web-flutter-version passes with "read from .fvmrc".