Support Bash 3.0

[Chemaclass]

Summary

Closes: #468 by @akinomyoga

Lower the minimum Bash version requirement from 3.2 to 3.0.

Changes

• Replace Bash 3.1+ features with 3.0 compatible alternatives
• Fix assert_contains_ignore_case to use tr instead of shopt nocasematch
• Handle empty strings in printf '%q' and data providers
• Separate array declaration from assignment for Bash 3.0 compatibility
• Skip release_test.sh on Bash 3.0 (release.sh requires 3.1+)
• Add CI workflow to test all modes on Bash 3.0 in parallel

[Chemaclass]

@akinomyoga thank you for the review! I addressed all your feedback, please let me know if you find anything else

[akinomyoga]

I haven't actually gone through the PR. I can later check it in detail.

[akinomyoga]

The regular expressions used in the following lines do not work in an intended way in Bash < 3.2.

src/coverage.sh:516:        if [[ $brace_count -eq 0 && "$line" =~ \{ && "$line" =~ \} ]]; then
install.sh:61:  [[ "$1" =~ ^[0-9]+\.[0-9]+\.[0-9]+$ || "$1" == "latest" || "$1" == "beta" ]]
release.sh:532:  if [[ ! "$version" =~ ^[0-9]+\.[0-9]+\.[0-9]+$ ]]; then
src/learn.sh:861:  [[ $1 =~ ^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$ ]]

It seems you assign the regular expression to a variable and use it as [[ ... =~ $variable ]], but I recommend you to define a function like bashunit::regex_match() { [[ $1 =~ $2 ]]; } so that you can call bashunit::regex_match "$line" '\{', etc.

[akinomyoga]

Bash-3.0 has a bug that the replacements of line="${line//\[failed\]/$'\n'}" becomes '<newline>' instead of <newline>. See this example:

$ script='line="${line//2/$'\''\n'\''}"; echo "$line"'
$ echo "$script"
line="${line//2/$'\n'}"; echo "$line"
$ line=123 bash-3.0 -c "$script"
1'
'3
$ line=123 bash-3.1 -c "$script"
1
3

The solution is not to quote the right-hand side (RHS) of the assignment:

$ script='line=${line//2/$'\''\n'\''}; echo "$line"'
$ echo "$script"
line=${line//2/$'\n'}; echo "$line"
$ line=123 bash-3.0 -c "$script"
1
3
$ line=123 bash-3.1 -c "$script"
1
3

In the first place, the quoting of the RHSs of assignments is redundant because the RHSs are not subject to word splitting or pathname expansions (aka glob expansions). The only cases where quoting of the RHSs of assignments is needed are the case where the RHS contains shell special characters (such as whitespace or delimiters like ;&|<> and the case where the RHS contains expansions like "$*" or "${arr[*]}" with a custom IFS.

[akinomyoga]

If these are intentional because those functions are ensured to be called in a context where IFS is properly set, please ignore the following comments.

[akinomyoga]

LGTM