Classify function assignment names as function semantic tokens

[wmsci]

Hi,

I noticed this issue with the syntax highlighting while using languageserver with the R extension for Visual Studio Code in Cursor. I tried fixing it myself and it works on my machine, so I'm opening this PR in case it is useful.

Problem

When a function is defined with fn <- function() {} and later used as a function call, fn(), those two uses of fn get different semantic token types.

The function call is a SYMBOL_FUNCTION_CALL, so it is marked function. The name on the left of the assignment is only a SYMBOL, so it is marked variable.

Themes colour those types separately, so the same name is coloured differently at the definition and at the function call.

Completion already treats these assigned names as functions (scope_completion_functs_xpath in R/completion.R).

Before

After

Fix

After the default parse-data map, reclassify a SYMBOL as a function token with the declaration modifier when it is the left-hand name of:

• fn <- function() {}
• fn = function() {}
• fn <- \(x) {}

The same rule is applied on the XML fallback path.

Testing

• Added cases in tests/testthat/test-semantic-tokens.R