[BUGZILLA #17831] numericDeriv alters result of eval

[github-actions]

Reported by Raimundo Neto on R-devel 2020-06-15.

Simple example that fails:

 x <- 0
 tryCatch(numericDeriv(quote(sqrt(-x)), "x"), error = identity)
 stopifnot(x == 0)

We save and restore the theta value but don't guard against a jump.
We could put in a cleanup handler at the C level.

Cleaner is probably to push another frame with the variable to change
on the environment. At the R level this can be done in numericDeriv by
changing

val <- .Call(C_numeric_deriv, expr, theta, rho, dir)

to

rho1 <- new.env(parent = rho)
assign(theta, get(theta, rho), rho1)
val <- .Call(C_numeric_deriv, expr, theta, rho1, dir)

Might be better to make the analogous change at C level though as we
document numeric_deriv in R-exts.texi.

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METADATA

• Bug author - Luke Tierney
• Creation time - 2020-06-16 14:27:28 UTC
• Bugzilla link
• Status - NEW
• Alias - None
• Component - Low-level
• Version - R 4.0.x
• Hardware - All All
• Importance - P5 normal
• Assignee - R-core
• URL -