Handling of $$ in value

[shawkins]

The current handling will replace $$ in a value with a single $ - this is due to the internal escaping behavior, which escapes escapes $ as $$. However this behavior isn't documented and can be surprising to users. Should

smallrye-config/implementation/src/main/java/io/smallrye/config/ExpressionConfigSourceInterceptor.java

Line 101 in 5a96de2

int index = value.indexOf("\\$");

also account for $$, or should this behavior be documented?

I don't mind submitting a patch if it's the former.

[radcortez]

The $$ is indeed used as an escape sequence to not expand on expressions.

That particular piece is yet another rule added by MP Config, in which \$ should act as an escape sequence for expressions. Please check #746 for more context.

I believe the expression code blindly escapes expressions with the double $, because there is a flag that can be used to omit the brackets and treat the value as an expression. At this stage, we are never going to turn that flag on, so maybe we can make the escape smarter and only work if square brackets are found after?