subApp cannot find data directory

subApp_data_path.Rmd

---
title: "SubApp path to data"
author: "Ian Lyttle"
runtime: shiny
output: 
  html_document:
    theme: united
---

This is a case where a subApp behaves differently from an app.

To reproduce this, you will have to create a directory for the app, then write out the app and the data.

Define/create our directories:

```{r directories}
app_path <- file.path("app")
dir.create(app_path) # warning: may generate warning 

data_path <- file.path(app_path, "data")
dir.create(data_path) # same warning
```

Let's start with the data:

```{r csv_create}
write.csv(
  data.frame(x = seq(1, 5), y = seq(1, 5)),
  file.path(data_path, "linear.csv"),
  row.names = FALSE
)
```

Let's write out a short app.

```{r}
txt_ui <- "
library(shiny)
library(ggvis)

shinyUI(fluidPage(

  fluidRow(
    column(3, wellPanel()),
    column(6, ggvisOutput('gg_linear')),
    column(3, wellPanel())
  )

))
" 

txt_server <- "
library(shiny)
library(ggvis)

shinyServer(function(input, output, session) {

  data <- read.csv(
    file.path('data', 'linear.csv'),
    header = TRUE
  )

  data %>% 
    ggvis(x = ~x, y = ~y) %>% 
    layer_points() %>% 
    bind_shiny('gg_linear')

})
"

cat(txt_ui, file = file.path(app_path, "ui.R"))
cat(txt_server, file = file.path(app_path, "server.R"))
```

Let's run this app within this page:

```{r}
shinyAppDir(app_path)
```

### What I find

Running this document using the "Run Document" button, then rendering in the browser, the subApp cannot find the data directory.

Running the app from the command line, shiny finds everything OK.