[NopeCharon]

What type of PR is this?

bug

Which issue does this PR fix:

Fixes #809

What does this PR do / Why do we need it:

When a substitution KEY=value is provided, substitute() rejects the stacker file if it contains the shell-style placeholder $KEY. The check was strings.Contains(content, "$KEY"), which also matches any variable whose name just starts with KEY. As a result, stacker build --substitute VERSION=1.0 failed on a run section that uses $VERSION_ID from /etc/os-release:

error "VERSION=1.0" was provided as a substitution and unsupported placeholder "$VERSION" was found. ...
1 instances of unsupported placeholders found. Review log for how to update.

This PR reports $KEY only when it is not followed by another variable-name character ([A-Za-z0-9_]), using a regexp built with regexp.QuoteMeta. The ${KEY} and ${KEY:...} checks already require an exact key match, so they are unchanged. The substitution syntax docs now mention this behavior.

If an issue # is not available please add repro steps and logs showing the issue:

See #809.

Testing done on this change:

Extended TestSubstitute:

• $VERSION_ID $VERSIONS ${VERSION_ID} ${VERSIONS:-1} ${{VERSION}} with VERSION=1.0 now substitutes successfully and leaves the shell variables untouched.
• $VERSION, $VERSION/bin, $VERSION-rc1 and "$VERSION" are still rejected.

Without the fix, the new case fails:

--- FAIL: TestSubstitute (0.00s)
    types_test.go:116: failed substitution: 1 instances of unsupported placeholders found. Review log for how to update.

With the fix, go test ./pkg/types/ passes (on linux/arm64, using the Makefile's go-test build tags):

--- PASS: TestSubstitute (0.00s)
...
ok  	stackerbuild.io/stacker/pkg/types	0.017s

Automation added to e2e:

No. The behavior is covered by the TestSubstitute unit test.

Will this break upgrades or downgrades?

No.

Does this PR introduce any user-facing change?:

Shell variables whose names start with a provided substitution key (e.g. `$VERSION_ID` with `--substitute VERSION=...`) no longer cause an "unsupported placeholder" error.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

❌ Patch coverage is 85.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 12.94%. Comparing base (715bf05) to head (977b312).

Files with missing lines	Patch %	Lines
pkg/types/stackerfile.go	85.00%	2 Missing and 1 partial ⚠️

❗ There is a different number of reports uploaded between BASE (715bf05) and HEAD (977b312). Click for more details.

HEAD has 37 uploads less than BASE

Flag	BASE (715bf05)	HEAD (977b312)
	40	3

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #810       +/-   ##
===========================================
- Coverage   55.06%   12.94%   -42.12%     
===========================================
  Files          55       55               
  Lines        5911     5924       +13     
===========================================
- Hits         3255      767     -2488     
- Misses       2085     5030     +2945     
+ Partials      571      127      -444     

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