Fix aspire deploy of Python apps when uv.lock doesn't exist

[Copilot]

Problem

Running aspire deploy on a Python project using UV package manager fails when the uv.lock file doesn't exist. This happens when deploying without running aspire run first:

docker buildx (stderr): ERROR: failed to build: failed to solve: failed to compute
cache key: failed to calculate checksum of ref ngtgltiej6cnsp6a6149o0sm2::dz4b7s2gighc6by5chyfoyue0: "/app/uv.lock": not found

The generated Dockerfile attempted to bind mount uv.lock and use the --locked flag with uv sync, but the file only exists after running aspire run locally (via WithUvEnvironment()).

Solution

Modified the Dockerfile generation logic to check if uv.lock exists and generate appropriate Docker commands:

When uv.lock exists (after running locally):

• Uses --locked flag with bind mounts for reproducible builds
• Ensures consistent dependency versions across builds

When uv.lock doesn't exist (first-time deploy):

• Copies only pyproject.toml to the container
• Runs uv sync without --locked to generate the lock file during Docker build
• Allows deployment without running the app locally first

Example Dockerfile Changes

Before (always expected uv.lock):

RUN --mount=type=bind,source=uv.lock,target=uv.lock \
    --mount=type=bind,source=pyproject.toml,target=pyproject.toml \
    uv sync --locked --no-install-project --no-dev

After (when uv.lock doesn't exist):

COPY pyproject.toml /app/
RUN --mount=type=cache,target=/root/.cache/uv \
    uv sync --no-install-project --no-dev

This allows aspire deploy to work on a fresh clone of a Python project without requiring aspire run to be executed first.

Fixes #8862

cc @davidfowl @mitchdenny

Original prompt

---

This section details on the original issue you should resolve

<issue_title>aspire deploy of the py-starter app without running first fails</issue_title>
<issue_description>Error is:

dotnet(66820) stdout:       docker buildx (stderr): ERROR: failed to build: failed to solve: failed to compute
cache key: failed to calculate checksum of ref ngtgltiej6cnsp6a6149o0sm2::dz4b7s2gighc6by5chyfoyue0: "/app/uv.lock": not found

This is because we removed the uv.lock file. It gets generated when we run uv sync which only happens during aspire run.

We should ensure uv sync runs first, or somehow else fix the dockerfile.

cc @davidfowl @mitchdenny </issue_description>

<agent_instructions>This is the docker file, we need to handle when uv sync has never run outside of the docker file as well.

aspire/src/Aspire.Hosting.Python/PythonAppResourceBuilderExtensions.cs

Lines 412 to 416 in 4137844

	.RunWithMounts(
	"uv sync --locked --no-install-project --no-dev",
	"type=cache,target=/root/.cache/uv",
	"type=bind,source=uv.lock,target=uv.lock",
	"type=bind,source=pyproject.toml,target=pyproject.toml")

</agent_instructions>

Comments on the Issue (you are @copilot in this section)

Fixes #12237

---

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[github-actions]

🚀 Dogfood this PR with:

⚠️ WARNING: Do not do this without first carefully reviewing the code of this PR to satisfy yourself it is safe.

curl -fsSL https://raw.githubusercontent.com/dotnet/aspire/main/eng/scripts/get-aspire-cli-pr.sh | bash -s -- 12240

Or

• Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/dotnet/aspire/main/eng/scripts/get-aspire-cli-pr.ps1) } 12240"

[github-actions]

🚀 Dogfood this PR with:

⚠️ WARNING: Do not do this without first carefully reviewing the code of this PR to satisfy yourself it is safe.

curl -fsSL https://raw.githubusercontent.com/dotnet/aspire/main/eng/scripts/get-aspire-cli-pr.sh | bash -s -- 12240

Or

• Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/dotnet/aspire/main/eng/scripts/get-aspire-cli-pr.ps1) } 12240"

[davidfowl]

OK this works!

[Copilot]

Pull Request Overview

This PR fixes a deployment issue where aspire deploy fails for Python applications using the UV package manager when uv.lock doesn't exist. The fix implements conditional Dockerfile generation based on whether uv.lock is present in the project directory.

Key changes:

• Added runtime detection of uv.lock file existence before generating Dockerfiles
• Implemented two different Dockerfile generation paths: one for locked mode (when uv.lock exists) and one for unlocked mode (when it doesn't)
• Added comprehensive test coverage for the new unlocked mode scenario

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/Aspire.Hosting.Python/PythonAppResourceBuilderExtensions.cs	Added logic to check for uv.lock existence and generate appropriate Docker commands for locked vs unlocked scenarios
tests/Aspire.Hosting.Python.Tests/AddPythonAppTests.cs	Added new test WithUvEnvironment_GeneratesDockerfileInPublishMode_WithoutUvLock to verify Dockerfile generation without uv.lock
tests/Aspire.Hosting.Python.Tests/Snapshots/AddPythonAppTests.WithUvEnvironment_GeneratesDockerfileInPublishMode_WithoutUvLock#00.verified.txt	Snapshot verification for script entrypoint Dockerfile without uv.lock
tests/Aspire.Hosting.Python.Tests/Snapshots/AddPythonAppTests.WithUvEnvironment_GeneratesDockerfileInPublishMode_WithoutUvLock#01.verified.txt	Snapshot verification for module entrypoint Dockerfile without uv.lock
tests/Aspire.Hosting.Python.Tests/Snapshots/AddPythonAppTests.WithUvEnvironment_GeneratesDockerfileInPublishMode_WithoutUvLock#02.verified.txt	Snapshot verification for executable entrypoint Dockerfile without uv.lock