String interpolation

[Kampfkarren]

Implements the string interpolation RFC (#165).

TODOs are commented as "INTERP TODO:", things I want highlighted in code review as "INTERP CODE REVIEW:"

This is going to diverge from RFC a bit in making {{ a syntax error, as you never want to format a table you just created, and it is likely to be a common error from those coming from Rust or Python when escaping braces.

local name = "world"
print(`Hello {name}!`) -- Hello world!

Big TODOs:

• FFlag (Does not include %* string.format specifier)
• Check that this resolves to string
• Does other work need to be done for linters/type checker?
• JSON encoder?
• Fix MSVC compiler warnings
• Reserve, implement, or concretely reject format specifiers -- Needs comment from maintainers
• Support f`x`

[Kampfkarren]

Also reminding myself I need a should have a test for something like f`` within an interpolation expression

[Kampfkarren]

Without changing anything about Autocomplete.cpp, this test passed, and properly didn't pass when I put @1 outside of braces:

TEST_CASE_FIXTURE(ACFixture, "autocomplete_interpolated_string")
{
    check(R"(f(`expression = {@1}`))");

    auto ac = autocomplete('1');
    CHECK(ac.entryMap.count("table"));
    CHECK_EQ(ac.context, AutocompleteContext::Expression);
}

Not sure why immediately.

Do I also need to handle making sure that pressing one backtick creates the other?

[alexmccord]

Without changing anything about Autocomplete.cpp, this test passed, and properly didn't pass when I put @1 outside of braces:

Ah, my bad. It worked out for free in our case, because autocomplete will look up for the best scope given a location in the document, which is what happened in the test above.

Do I also need to handle making sure that pressing one backtick creates the other?

I don't think so, this sounds like a script editor feature. I don't think there's any extra special behavior we'd want autocompleter to do here, so if it works let's call it a day for that.

[alexmccord]

LGTM. This is fantastic work!

[zeux]

Thanks for working through this! Just a heads up that I submitted a couple commits to this PR to make it merge-ready, most significantly outlawing the function calls without parentheses yet again - this will be added back to the RFC: #648. We may add this in the future but there are some exciting possibilities for how string interpolation interacts with DSLs and I'd like to keep this road open even if we end up not taking it for now. No action necessary since I've updated both the RFC and this PR accordingly, but third party implementations like full-moon may need to get updated.

[Kampfkarren]

Doesn't look like there's anything I filed left :)