RFR: 8341641: Make %APPDATA% and %LOCALAPPDATA% env variables available in *.cfg files [v3]

[Alexey Semenyuk]

On Thu, 6 Mar 2025 15:25:13 GMT, Alexey Semenyuk <asemenyuk at openjdk.org> wrote:

>> jpackage app laucnher will expand environment variables in .cfg files.
>> 
>> Previously jpackage app launcher only replaced `$APPDIR`, `$BINDIR`, and `$ROOTDIR` tokens with the corresponding path values. With this patch, any environment variable can be expanded. The syntax is shell-like `$ENV_VAR_NAME` or `${ENV_VAR_NAME}`. If `$ENV_VAR_NAME` syntax is used, the variable name stops at the first character outside of `[a-zA-Z0-9_]` character range. If `${ENV_VAR_NAME}` syntax is used, the variable name stops at the first `}` character after `${` substring. E.g:
>> | String    | Variables | Variable Values | Expanded string | Note |
>> | -------- | ------- |------- |------- |------- |
>> | <pre>Welcome $USER!</pre>  | <pre>USER</pre> | <pre>USER=John</pre> | <pre>Welcome John!</pre> ||
>> | <pre>Welcome $USER!</pre>  | <pre>USER</pre> | <pre>not set</pre> | <pre>Welcome $USER!</pre> | Unset variables are not expanded. |
>> | <pre>Welcome $USER2</pre> | <pre>USER2</pre>   | <pre>USER2=John</pre> | <pre>Welcome John!</pre> ||
>> | <pre>Welcome ${USER}2</pre> | <pre>USER</pre>  | <pre>USER=John</pre> | <pre>Welcome John2!</pre> ||
>> | <pre>Welcome $USER-2</pre> | <pre>USER</pre>   | <pre>USER=John</pre> | <pre>Welcome John-2!</pre> ||
>> | <pre>Welcome ${USER-2}</pre> | <pre>USER-2</pre>   | <pre>USER-2=John</pre> | <pre>Welcome John!</pre> | `USER-2` is likely to be an invalid env variable name, but jpackage launcher is not validating names. |
>> 
>> `$` character combination prevents variable expansion:
>> | String    | Variables | Variable Values | Expanded string |
>> | -------- | ------- |------- |------- |
>> | <pre>Hello \$A! Bye $B</pre>  | B | <pre>B=John</pre> | <pre>Hello $A! Bye John</pre> |
>> | <pre>Hello \${A}! Bye $B</pre>  | B | <pre>B=John</pre> | <pre>Hello ${A}! Bye John</pre> |
>> 
>> `\` character combination escapes ``:
>> | String    | Variables | Variable Values | Expanded string |
>> | -------- | ------- |------- |------- |
>> | <pre>Hello \\\$A! Bye $B</pre>  | A, B | <pre>A=Ana</pre><pre>B=John</pre> | <pre>Hello \\Ana! Bye John</pre> |
>> 
>> If `` character is not followed by another `` character or `$` character, it is interpreted as a regular character:
>> | String    | Expanded string |
>> | -------- | ------- |
>> |<pre>a\\b\\c</pre>|<pre>a\\b\\c</pre>|
>> 
>> 
>> Expansion is non-recursive:
>> | String    | Variables | Variable Values | Expanded string | Note |
>> | -------- | ------- |------- |------- |------- |
>> | <pre>Hello $A!</pre>  | A | <pre>A=$B...
>
> Alexey Semenyuk has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Merge branch 'JDK-8341641-master' of https://github.com/alexeysemenyukoracle/jdk into JDK-8341641-master
>  - Formatting fixed

This is true for any shell behavior. It is also true that some shells fail to expand undefined variables if configured accordingly. Bash, for example:

bash -c 'FOO=10; echo FOO=$FOO; unset FOO; set -u; echo FOO=$FOO'

Output:

FOO=10
bash: line 1: FOO: unbound variable


.cfg files are not scripts and jpackage app launcher is not an interpreter. Performed string substitution is less variable expansion and more token replacement; if token value is not available, it is not replaced.
Regardless of handling undefined variables, users have to deal with the consequences. Say they pass `--java-options -DmyAppData=$HOME/.myData` option to jackage and `HOME` variable happens undefined on a machine where installed app is launched. How would `/.myData` be better than `$HOME/.myData`? At least it is clear something went wrong in the second case.

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PR Comment: https://git.openjdk.org/jdk/pull/23923#issuecomment-2704734396