fix: handle heredoc in Dockerfile

[dotzborro]

Fixes: #8160 #9472

Description
COPY commands are read from Dockerfile files for caching mechanism. Even before this PR, when source argument of COPY command comes from the web (http/https), it is ignored. However, since version 1.4 heredoc support was added and as per my understanding it should be handled similarly.

Example of heredoc in Dockerfile:

COPY <<EOF /entrypoint.sh
#!/bin/bash
echo "hello!"
EOF

Current version of Skaffold, when such construction is encountered fails with:

Checking cache...
 - [redacted]: Error checking cache.
getting hash for artifact "[redacted]": getting dependencies for "[redacted]": file pattern [<<EOF] must match at least one file

This PR:

• makes << to be handled similarly to http/https
• adds unit tests for ReadCopyCmdsFromDockerfile function

[gemini-code-assist]

Summary of Changes

Hello @dotzborro, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses issues #8160 and #9472 by adding support for heredoc syntax in Dockerfiles. The changes ensure that Skaffold correctly identifies and skips heredoc dependencies during cache checking, preventing errors and improving the overall build process. The PR also includes new unit tests to validate the implemented functionality.

Highlights

• Heredoc Support: The PR introduces support for handling heredoc syntax (<<EOF) within Dockerfiles, similar to how http:// and https:// sources are treated in COPY commands. This prevents Skaffold from attempting to resolve heredoc specifiers as file paths.
• Dependency Handling: Updates the readCopyCommand function to recognize and skip heredoc dependencies, preventing errors during cache checking.
• Unit Tests: Adds new unit tests to verify the correct behavior of ReadCopyCmdsFromDockerfile function, including scenarios with and without COPY commands, file existence checks, and handling of http/https/heredoc sources.

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[gemini-code-assist]

Code Review

The code changes enhance the handling of heredoc syntax in Dockerfiles by treating << similarly to http and https prefixes, preventing Skaffold from attempting to watch these as local file dependencies. Additionally, unit tests were added to verify the correct behavior of the ReadCopyCmdsFromDockerfile function.

[gemini-code-assist]

Consider adding a test case with a heredoc that contains spaces or tabs before the EOF to ensure that the prefix matching is robust.

[dotzborro]

not sure if I'm getting it right, but the actual parsing is provided by github.com/moby/buildkit/frontend/dockerfile/parser and thus testing the parser does not fall in Skaffold scope.

[plumpy]

Thanks for sending this!