Build cache should exclude `.aws-sam` in md5 calculation

Description:

Running sam build --cached always reports that the cache is invalid despite no code changes.

Steps to reproduce:

Run sam build --cached twice. The second run doesn’t use the cache.

Observed result:

The cache is deemed invalid and not used despite no code changes.

Expected result:

The cache is used when the code isn’t changed between builds.

Additional environment details (Ex: Windows, Mac, Amazon Linux etc)

1. OS: OS X 10.15.7 (Catalina), Windows 10
2. sam --version: SAM CLI, version 1.23.0
3. AWS region: eu-west-1

Problem

The CLI stores the directory hash in .aws-sam/build.toml. This file is also used when calculating the directory hash. Consider this scenario:

• The developer writes some code. The code directory is now in State 1.
• A build is run and it finds that the directory hash in build.toml doesn’t equal hash(State 1)
• SAM deems the cache invalid and rebuilds
• At the end of the build SAM saves hash(State 1) in build.toml
• Saving the hash means that the directory is no longer in State 1 but State 2
• The developer changes no code and runs another build
• SAM compares the hash in build.toml - which is hash(State 1) - and finds it is not equal to the hash of the current state, State 2
• SAM rebuilds again and saves hash(State 2) in build.toml, which is now in State 3 due to this update
• And so on

Workaround

This issue can be worked around by specifying -b, --build-dir DIRECTORY when calling sam build. Specifying a directory outside of the code directory results in SAM using the cache.

Possible Solutions

How do we solve this issue? Would we be able to ignore .aws-sam/build.toml when calculating the hash?

[aahung]

Oh that’s why, thanks for providing the information. As a workaround, you can continue to use -b option or put the source code into a subfolder and set a CodeUri to <sub-folder-name>.

[github-actions[bot]]

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