fix(R microkernel): Capture plots and avoid recursive print calls

rust/kernel-r/src/lib.rs

@@ -21,7 +21,7 @@ mod tests {
         stencila_schema::Node,
         KernelTrait,
     };
-    use test_utils::{assert_json_eq, serde_json::json, skip_ci};
+    use test_utils::{assert_json_eq, print_logs, serde_json::json, skip_ci};
 
     async fn skip_or_kernel() -> Result<MicroKernel> {
         if skip_ci("Failing on Linux and MacOS CIs") {
@@ -249,4 +249,26 @@ mod tests {
 
         Ok(())
     }
+
+    #[tokio::test]
+    async fn encode_plots() -> Result<()> {
+        let mut kernel = match skip_or_kernel().await {
+            Ok(kernel) => kernel,
+            Err(..) => return Ok(()),
+        };
+
+        print_logs();
+
+        for code in ["plot(1)", "hist(rnorm(1000), breaks=30)"] {
+            let (outputs, messages) = kernel.exec(code).await?;
+            assert_json_eq!(messages, json!([]));
+            let image = match &outputs[0] {
+                Node::ImageObject(dt) => dt.clone(),
+                _ => bail!("unexpected type {:?}", outputs[0]),
+            };
+            assert!(image.content_url.starts_with("data:image/png;base64,"));
+        }
+
+        Ok(())
+    }
 }

rust/kernel-r/src/r-codec.r

@@ -1,5 +1,9 @@
-if (!suppressPackageStartupMessages(require("jsonlite", quietly=TRUE)))
-  install.packages("jsonlite")
+for (pkg in c("jsonlite", "base64enc")) {
+  if (!suppressPackageStartupMessages(require(pkg, character.only = TRUE, quietly=TRUE))) {
+    install.packages(pkg, quiet = TRUE)
+    suppressPackageStartupMessages(require(pkg, character.only = TRUE, quietly=TRUE))
+  }
+}
 
 # Decode JSON to a R value
 decode_value <- function(json) {
@@ -23,7 +27,7 @@ convert_value <- function(value, options = list()) {
   } else if (inherits(value, "table")) {
     # The functions `summary` and `table` return class "table" results
     # Currently, just "print" them. In the future, we may convert these to Datatables.
-    paste(utils::capture.output(print(value)), collapse = "\n")
+    paste(utils::capture.output(base::print(value)), collapse = "\n")
   } else if (is.data.frame(value)) {
     # Decode to a Datatable
     convert_data_frame(value)
@@ -42,7 +46,7 @@ convert_value <- function(value, options = list()) {
     value
   } else {
     warning(paste("Default conversion for R type:", typeof(value), ", class:", class(value)))
-    paste(utils::capture.output(print(value)), collapse = "\n")
+    paste(utils::capture.output(base::print(value)), collapse = "\n")
   }
 }
 
@@ -68,12 +72,12 @@ convert_plot <- function(value, options = list(), format = "png") {
     units = "cm",
     res = 150
   )
-  print(value)
+  base::print(value)
   grDevices::dev.off()
 
   list(
     type = unbox("ImageObject"),
-    contentUrl = unbox(paste0("data:image/", format, ";base64,", base64enc::base64encode(filename)))
+    contentUrl = unbox(paste0("data:image/", format, ";base64,", base64encode(filename)))
   )
 }
 

rust/kernel-r/src/r-kernel.r

@@ -18,6 +18,11 @@ info <- function(msg) message(msg, "CodeInfo")
 warning <- function(msg) message(msg, "CodeWarning")
 error <- function(error, type = "RuntimeError") message(error$message, type)
 
+# Default graphics device to avoid window popping up or `Rplot.pdf` polluting
+# local directory. Recording must be enabled for print devices.
+png(tempfile())
+dev.control("enable")
+
 stdin <- file("stdin", "r")
 while (TRUE) {
   code <- readLines(stdin, n=1)
@@ -28,6 +33,20 @@ while (TRUE) {
     error(compiled, "SyntaxError")
   } else {
     value <- tryCatch(eval(compiled), message=info, warning=warning, error=error)
+
+    if (!withVisible(value)$visible) {
+      value <- NULL
+    }
+
+    rec_plot <- recordPlot()
+    if (!is.null(rec_plot[[1]])) {
+      value <- rec_plot
+      # Clear the existing device and create a new one
+      dev.off()
+      png(tempfile())
+      dev.control("enable")
+    }
+
     if (!is.null(value)) {
       last_line <- tail(strsplit(unescaped, "\\n")[[1]], n=1)
       assignment <- grepl("^\\s*\\w+\\s*(<-|=)\\s*", last_line)