windows: when necessary, discover R using registry curent version

Note that R_HOME and any version of R on the PATH are preferred to what is in the registry. Note also that R front ends like RStudio and R GUI will automatially set R_HOME, so when Quarto is run from within these environments it will use the same version of R as the host session.

Author: jjallaire

src/core/knitr.ts

@@ -24,7 +24,7 @@ export async function knitrCapabilities() {
   try {
     const result = await execProcess({
       cmd: [
-        rBinaryPath("Rscript"),
+        await rBinaryPath("Rscript"),
         resourcePath("capabilities/knitr.R"),
       ],
       stdout: "piped",

src/core/registry.ts

@@ -0,0 +1,49 @@
+/*
+* registry.ts
+*
+* Copyright (C) 2020 by RStudio, PBC
+*
+*/
+
+import { execProcess } from "./process.ts";
+
+export const kHKeyCurrentUser = "HKCU";
+export const kHKeyLocalMachine = "HKLM";
+
+export async function registryReadString(
+  root: string | string[],
+  key: string,
+  value: string,
+): Promise<string | undefined> {
+  // if an array is passed then call each one in turn
+  if (Array.isArray(root)) {
+    for (const r of root) {
+      const val = registryReadString(r, key, value);
+      if (val !== undefined) {
+        return val;
+      }
+    }
+    return undefined;
+  }
+
+  // run reg query
+  const kTypeString = "REG_SZ";
+  const cmd = [
+    "reg",
+    "query",
+    `${root}\\${key}`,
+    "/v",
+    value,
+  ];
+  const result = await execProcess({
+    cmd,
+    stdout: "piped",
+  });
+  if (result.success && result.stdout) {
+    const typePos = result.stdout?.indexOf(kTypeString);
+    if (typePos !== -1) {
+      return result.stdout.substring(typePos + kTypeString.length).trim();
+    }
+  }
+  return undefined;
+}

src/core/resources.ts

@@ -7,7 +7,13 @@
 
 import { existsSync, walkSync } from "fs/mod.ts";
 import { join } from "path/mod.ts";
+import { which } from "./path.ts";
 import { quartoConfig } from "./quarto.ts";
+import {
+  kHKeyCurrentUser,
+  kHKeyLocalMachine,
+  registryReadString,
+} from "./registry.ts";
 
 export function resourcePath(resource?: string): string {
   const sharePath = quartoConfig.sharePath();
@@ -26,13 +32,40 @@ export function binaryPath(binary: string): string {
   return join(quartoConfig.binPath(), binary);
 }
 
-export function rBinaryPath(binary: string): string {
+export async function rBinaryPath(binary: string): Promise<string> {
+  // if there is an R_HOME then respect that
   const rHome = Deno.env.get("R_HOME");
   if (rHome) {
-    // If there is an R_HOME, respect that.
     return join(rHome, "bin", binary);
-  } else if (Deno.build.os === "windows") {
-    // On windows, try to find R in program files
+  }
+
+  // then check the path
+  const path = await which(binary);
+  if (path) {
+    return path;
+  }
+
+  // on windows check the registry for a current version
+  if (Deno.build.os === "windows") {
+    // determine current version
+    const version = await registryReadString(
+      [kHKeyLocalMachine, kHKeyCurrentUser],
+      "Software\\R-core\\R",
+      "Current Version",
+    );
+    // determine path to version
+    if (version) {
+      const installPath = await registryReadString(
+        [kHKeyLocalMachine, kHKeyCurrentUser],
+        `Software\\R-core\\R\\${version}`,
+        "InstallPath",
+      );
+      if (installPath) {
+        return join(installPath, "bin", binary);
+      }
+    }
+
+    // last ditch, try to find R in program files
     const progFiles = Deno.env.get("programfiles");
     if (progFiles) {
       // Search program files for the binary
@@ -49,7 +82,7 @@ export function rBinaryPath(binary: string): string {
     }
   }
 
-  // We couldn't find R, just pass the binary itself and hope its on the path!
+  // We couldn't find R, just pass the binary itself and hope it works out!
   return binary;
 }
 

src/execute/rmd.ts

@@ -145,7 +145,7 @@ async function callR<T>(
     const result = await execProcess(
       {
         cmd: [
-          rBinaryPath("Rscript"),
+          await rBinaryPath("Rscript"),
           resourcePath("rmd/rmd.R"),
         ],
         stderr: quiet ? "piped" : "inherit",