Merge pull request #424 from rstudio/bugfix/zero-arg-sourcerefs

Handle zero-argument outputs gracefully

R/shiny.R

@@ -602,8 +602,16 @@ ShinySession <- setRefClass(
 #' @export
 `$<-.shinyoutput` <- function(x, name, value) {
   label <- deparse(substitute(value))
-  attr(label, "srcref") <- srcrefFromShinyCall(substitute(value)[[2]])
-  attr(label, "srcfile") <- srcFileOfRef(attr(substitute(value)[[2]], "srcref")[[1]])
+  if (length(substitute(value)) > 1) {
+    # value is an object consisting of a call and its arguments. Here we want
+    # to find the source references for the first argument (if there are
+    # arguments), which generally corresponds to the reactive expression--
+    # e.g. in renderTable({ x }), { x } is the expression to trace.
+    attr(label, "srcref") <- srcrefFromShinyCall(substitute(value)[[2]])
+    srcref <- attr(substitute(value)[[2]], "srcref")
+    if (length(srcref) > 0)
+      attr(label, "srcfile") <- srcFileOfRef(srcref[[1]])
+  }
   .subset2(x, 'impl')$defineOutput(name, value, label)
   return(invisible(x))
 }

R/utils.R

@@ -488,6 +488,8 @@ checkAsIs <- function(options) {
 srcrefFromShinyCall <- function(expr) {
   srcrefs <- attr(expr, "srcref")
   num_exprs <- length(srcrefs)
+  if (num_exprs < 1)
+    return(NULL)
   c(srcrefs[[1]][1], srcrefs[[1]][2],
     srcrefs[[num_exprs]][3], srcrefs[[num_exprs]][4],
     srcrefs[[1]][5], srcrefs[[num_exprs]][6])