R devel - May 2020 - round() and signif() do not check argument names when a single argument is given

Hi,

I was told to send this to the -devel list instead of posting to bugzilla.

When round our signif are called with a single named argument, R does not
check the name and runs the function with that named argument directly as
the first argument,  using 0.0 or 6.0 (6 in the case of signif) for the
second argument. Not checking the argument name is at odds with how all
other primitive functions are handled, and so I expect these to trigger an
error like other functions do.  I've tested in 4.0.0 code, but this
behavior might go back decades.

The cases are things like this:

#horse is not a legitimate argument
round(horse=3.1235)
[1] 3

#digits is a legitimate argument in round,
#but the value gets used without checking as the first argument.
round(digits=3.1135)
[1] 3

The second case is especially strange to me, because digits is a named
argument of the function.  No other functions behave this way as far as I
can tell; the first would normally either trigger a missing x value message
or an unused argument if it is a user function; the second would trigger a
warning about missing x.

Compare to:
>  log(base=3)
Error: argument "x" is missing, with no default

These two functions are handled in a  handler function in
src/main/arithmetic.c: do_Math2().  The strange cases get handled by the
code around line 1655 in src/main/arithmetic.c. The context is  n is the
number of arguments, but symbol names have not yet been checked:

if(n == 1) {
   double digits = 0.0;
   if(PRIMVAL(op) == 10004) digits = 6.0;
   SETCDR(args, CONS(ScalarReal(digits), R_NilValue));
}

Here, 10004 is the opcode symbol for signif and 10001 is for round, but
these are the only two ops handled by this function, so round uses
digits=0.0.  The SETCDR creates the argument list to be the current 1-item
list plus the new digits value set here, and then this gets passed to
do_math2.  do_math2 looks like it checks the arity of the arguments but not
the names, and calls fround or frpec on the arguments depending on the
opcode.

This case can be guarded against by adding a check for using the wrong
symbol name at this point, which only covers the case of calling these
functions with a single argument. This is essentially the same guard used
in other functions like do_log_bulitin  that is in the same file.

 if(n == 1 ){
static SEXP R_x_Symbol = NULL;
R_x_Symbol = install("x");
/*This handles single-argument calling*/
/*Make sure we don't call it with a mis-named argument:*/
if(CAR(args)==R_MissingArg ||
  TAG(args) != R_NilValue && TAG(args) != R_x_Symbol)
 error(_("argument \"%s\" is missing, with no default"),
"x");

   double digits = 0.0;
   if(PRIMVAL(op) == 10004) digits = 6.0;
   SETCDR(args, CONS(ScalarReal(digits), R_NilValue));
}

I'm not sure if CAR(args)==R_MissingArg is doing anything here, and
removing it seems to work, but this pattern is used in do_log_bultin.

I've tested this against the cases copied below, and this change will now
cause the error I expect in cases 5 and 6  [like round(digits=5.532) and
round(horse=5.131)],  whereas current R 4.0.0 does not. This change
includes some _() text, but I'm not sure whether that means it will impact
internationalization since the strings are identical to other error
messages.

In the R code below, I put these in tryCatch so you can save the text and
do a source() of the file. Both R 4.0.0 and the changed code correctly
cause errors in case 7/8, to demonstrate that these cases are not impacted
by the change.

##This tests various round/signif argument configurations
## Each of these should succeed/fail  the same if used in signif

cat("\nCase 1: round(1.12345): " )
cat(round(1.12345),"\n")

cat("\nCase 2: round(x=1.12345,2): ")
cat(round(x=1.12345,2),"\n")

cat("\nCase 3: round(x=1.12345,digits=2): ")
cat(round(x=1.12345,digits=2),"\n")

cat("\nCase 4: round(digits=2,x=1.12345): ")
cat(round(digits=2,x=1.12345),"\n")

cat("\nCase 4b: round(digits=2,1.12345): ")
cat(round(digits=2,1.12345),"\n")

## Current R 4.0 does not produce error but should
cat("\nCase 5: round(digits=x): \n")
tryCatch(
cat("round(digits=99.23456): ",  round(digits=99.23456)),
error=function(cond){print(paste("[Error in case]",cond))})


## Current R 4.0 does not produce error but should
cat("\nCase 6: round(banana=x): \n")
tryCatch(
  cat("round(banana=99.23456): ", round(banana=99.23456))
,error=function(cond){print(paste("[Error in case]",cond))})

## Error case
##error:
cat("\nCase 7: round(x=1.12345, digits=2, banana=3): ")

tryCatch( { cat(round(x=1.12345, digits=2, banana=3),"\n")},
   error=function(cond){print(paste("[Error in case]",cond))})

##error case
cat("\nCase 8 : round(x=1.12345, banana=3):  ")
tryCatch( round(x=1.12345, banana=3),
   error=function(cond){print(paste("[Error in case]",cond))})

	[[alternative HTML version deleted]]