fix: update ARG variable handling

[patrickhoefler]

This pull request introduces enhancements focusing on improving ARG variable substitution, simplifying code, and adding new tests to ensure correctness. The changes include replacing the ARG substitution mechanism with a more robust approach, introducing constants for Dockerfile instructions, and adding test cases to validate nested and unresolved ARG scenarios.

Closes #664.

[Copilot]

Pull Request Overview

Enhance ARG variable substitution in Dockerfile conversion, streamline constant usage, and add tests to cover nested and unresolved ARG scenarios.

• Introduce ArgReplacement slices with resolution helpers (appendAndResolveArgReplacement, stripRemainingArgPatterns)
• Define constants for Dockerfile instructions and precompile regex patterns
• Add tests for nested ARG substitution and ARG referencing before definition
• Update linter config to enable ineffassign and staticcheck

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
internal/dockerfile2dot/convert.go	Switch to slice-based ARG resolution, add constants, regex, helpers
internal/dockerfile2dot/convert_test.go	Add test cases for nested and unresolved ARG variable substitution
.golangci.yaml	Enable additional linters (ineffassign, staticcheck)

Comments suppressed due to low confidence (3)

internal/dockerfile2dot/convert.go:75

• The comment has a typo/grammar issue: 'set is at the name' should be 'set it as the name'.

// If there is an "AS" alias, set is at the name

internal/dockerfile2dot/convert_test.go:315

• Consider adding a test case for a stage-specific ARG (defined after the first FROM) to verify that the implementation correctly ignores or handles stage-scoped ARG variables.

args: args{

internal/dockerfile2dot/convert.go:217

• [nitpick] The function name 'appendAndResolveArgReplacement' is quite long; consider renaming to something more concise like 'resolveAndAppendArg' for readability.

func appendAndResolveArgReplacement(