use helper R function for getting tinytex bin

src/cpp/core/include/core/system/Xdg.hpp

@@ -31,16 +31,22 @@ namespace xdg {
  * All of these can be configured with environment variables as described below.
  */
 
-// Returns the RStudio XDG user config directory. On Unix-alikes, this is ~/.config/rstudio, or
-// XDG_CONFIG_HOME.
+// Returns the RStudio XDG user config directory.
+//
+// On Unix-alikes, this is ~/.config/rstudio, or XDG_CONFIG_HOME.
+// On Windows, this is 'FOLDERID_RoamingAppData' (typically 'AppData/Roaming').
 FilePath userConfigDir();
 
-// Returns the RStudio XDG user data directory. On Unix-alikes, this is ~/.local/share/rstudio, or
-// XDG_DATA_HOME
+// Returns the RStudio XDG user data directory.
+//
+// On Unix-alikes, this is ~/.local/share/rstudio, or XDG_DATA_HOME.
+// On Windows, this is 'FOLDERID_LocalAppData' (typically 'AppData/Local').
 FilePath userDataDir();
 
-// Returns the RStudio XDG system config directory. On Unix-alikes, this is /etc/rstudio, or
-// XDG_CONFIG_DIRS
+// Returns the RStudio XDG system config directory.
+//
+// On Unix-alikes, this is /etc/rstudio, XDG_CONFIG_DIRS.
+// On Windows, this is 'FOLDERID_ProgramData' (typically 'C:/ProgramData').
 FilePath systemConfigDir();
 
 } // namespace xdg

src/cpp/session/SessionModuleContext.cpp

@@ -1074,20 +1074,18 @@ bool addTinytexToPathIfNecessary()
 {
    if (isPdfLatexInstalled())
       return false;
-
-   FilePath binPath;
-
-#if defined(_WIN32)
-   FilePath appData(core::system::getenv("APPDATA"));
-   binPath = appData.complete("TinyTeX\\bin\\win32");
-#elif defined(__APPLE__)
-   binPath = resolveAliasedPath("~/Library/TinyTeX/bin/x86_64-darwin");
-#else
-   binPath = resolveAliasedPath("~/bin");
-#endif
-
-   if (binPath.childPath("pdflatex").exists())
-      core::system::addToSystemPath(binPath);
+
+   std::string binDir;
+   Error error = r::exec::RFunction(".rs.tinytexBin").call(&binDir);
+   if (error)
+      LOG_ERROR(error);
+
+   FilePath binPath = module_context::resolveAliasedPath(binDir);
+   if (!binPath.exists())
+      return false;
+
+   core::system::addToSystemPath(binPath);
+   return true;
 }
 
 bool isPdfLatexInstalled()

src/cpp/session/modules/SessionRMarkdown.R

@@ -462,4 +462,17 @@
       FALSE
 })
 
-
+.rs.addFunction("tinytexBin", function()
+{
+   if (!requireNamespace("tinytex", quietly = TRUE))
+      return(NULL)
+
+   # NOTE: binary directory has a single arch-specific subdir;
+   # rather than trying to hard-code the architecture we just
+   # infer it directly
+   root <- tinytex:::tinytex_root()
+   bin <- file.path(root, "bin")
+   subbin <- list.files(bin, full.names = TRUE)
+   subbin[[1]]
+
+})