Is it possible to inject a language inside a injected language?

[alemuller]

Some HDL, such VHDL, Verilog and GDL can be injected with PSL. But PSL have different flavors for each of this language, and PSL grammar uses rules (such expressions) from the injected language. For example a VHDL function call inside a PSL assertion:

-- psl assert a and foo(bar => baz);

Originally, I tried to to add PSL into VHDL grammar. But some PSL keywords (such x) are only valid inside the PSL context and are valid VHDL identifiers. It also dramatically increases the generate parser size.

Currently, I'm writing a PSL grammar with a subset of VHDL grammar, but this means the PSL grammar would only work when injected in VHDL language (but when used in Verilog or GDL).

Also. I haven't thought about the issues I will have when writing the highlight queries, what should I have in mind?

[Akvarion]

Maybe I'm writing the obvious, and for that I am sorry, but simple PSL grammar like the one you mentioned is already embedded in vhdl starting from vhdl-2008.
You can check the enhancements here:
doulos vhdl 2008 enhancements

[alemuller]

I'm aware.

But their relationship is complicated.

For instance:

PSL extends the grammar of VHDL expressions to allow PSL expressions, PSL built-in function calls, and PSL union expressions as sub expressions. Such extended expressions can only appear in a VHDL description within PSL declarations and PSL directives, or in a verification unit.

PSL and VHDL have different rules for identifiers.

PSL support VHDL ranges in some construction but not in others.

Initially I tried to implement PLS into VHDL grammar, but the parser size increased from about 3MB to over 10MB. Likely because the extra PSL tokens.

[maxbrunsfeld]

Yes, there is no restriction on the depth of nesting for syntax highlighting.

Currently, we do things like inject JSDoc within JavaScript within HTML within PHP.