Non-API calls conundrum

[lionel-]

https://rstudio.github.io/r-manuals/r-exts/The-R-API.html#moving-into-c-api-compliance

Non-problematic:

• SET_ENVFLAGS(): Remove env_unlock() #1705
• R_ClosureExpr() / BODY_EXPR(): Used in r_fn_body(), which is only used in zap_srcref(). Should be fine to call R-level body() instead.

Potentially problematic:

• SET_ENCLOS(): Used to mutate parent environment in quosure evaluation inside data masks. It would be helpful if we could continue to use it to avoid a perf hit when evaluating with many groups. See also Remove SET_ENCLOS() usage #1707

Problematic:

• SETLENGTH() / SET_TRUELENGTH(): Used in rlang C API for resizing. Would be nice to get these added to the official API. Also used in vctrs and data.table.

🔥🔥🔥 :

• R_PromiseExpr() / PREXPR(): Essential for tidyeval to access promise expressions.
  See also Remove PREXPR() usage (as much as we can) #1708

[lionel-]

SETLENGTH() / SET_TRUELENGTH(): Used in rlang C API for resizing.

@DavisVaughan proposed to use ALTREP views for resizing to length.

[lionel-]

Found non-API calls to R:

• ENVFLAGS Remove env_unlock() #1705
• FRAME Remove environment accessors #1721
• HASHTAB Remove environment accessors #1721
• LEVELS Remove LEVELS() accessor #1726
• NAMED 5634e96
• PRENV
• PRVALUE
• RDEBUG Remove usage of RDEBUG() and SET_RDEBUG() #1727
• R_PromiseExpr,
• Rf_findVarInFrame3
• SETLENGTH
• SET_BODY
• SET_CLOENV,
• SET_ENCLOS
• SET_ENVFLAGS Remove env_unlock() #1705
• SET_FORMALS
• SET_GROWABLE_BIT,
• SET_RDEBUG Remove usage of RDEBUG() and SET_RDEBUG() #1727
• SET_TRUELENGTH
• SET_TYPEOF
• STRING_PTR,
• XTRUELENGTH

[lionel-]

Requests/contribs for R core (WIP):

• C version of delayedAssign (needed for magrittr placeholder)
• Predicate to test if a binding is a promise (needed for rlang's env-printer, to prevent arbitrary executions while inspecting envs, etc). Could probably take the form of a "binding type" function that returns an extensible enum.
• To work around LEVELS() in (see rlang Remove LEVELS() accessor #1726), a predicate to determine if a CHARSXP is encoded in UTF8. Added in wch/r-source@0c753e4
• Version of getVar() that returns error codes? We either can't afford protecting ourselves from these jumpy R errors, or we'd like to throw our own errors with tailored messages r-devel/r-svn@29a2fda
  Or better, a function that returns the binding type:
  -> direct, promiseDelayed, promiseForced, active, missing, unbound.

Speculative:

• Iterator for attribute lists, to work around the removal of ATTRIB()?
  Or at least a way to get the attribute names?