From 8995588a7206ec986fa039b32afbec2ec3960962 Mon Sep 17 00:00:00 2001
From: Sergey Fedorov <sergey.fedorov@shopify.com>
Date: Tue, 30 Nov 2021 22:10:33 +0100
Subject: [PATCH] Add pager support into RubyLauncher

---
 .../truffleruby/launcher/RubyLauncher.java    | 44 ++++++++++++++++++-
 1 file changed, 43 insertions(+), 1 deletion(-)

diff --git a/src/launcher/java/org/truffleruby/launcher/RubyLauncher.java b/src/launcher/java/org/truffleruby/launcher/RubyLauncher.java
index 981222e4e5ee..2af9231dbc3b 100644
--- a/src/launcher/java/org/truffleruby/launcher/RubyLauncher.java
+++ b/src/launcher/java/org/truffleruby/launcher/RubyLauncher.java
@@ -10,12 +10,14 @@
 package org.truffleruby.launcher;
 
 import java.io.PrintStream;
+import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.lang.ProcessBuilder.Redirect;
 
 import org.graalvm.launcher.AbstractLanguageLauncher;
 import org.graalvm.nativeimage.ProcessProperties;
@@ -163,7 +165,7 @@ protected void collectArguments(Set<String> options) {
 
     @Override
     protected void printHelp(OptionCategory maxCategory) {
-        printHelp(System.out);
+        printHelp(getOutput());
     }
 
     @Override
@@ -173,6 +175,46 @@ protected AbortException abortUnrecognizedArgument(String argument) {
                 "truffleruby: invalid option " + argument + "  (Use --help for usage instructions.)");
     }
 
+    @Override
+    protected boolean runLauncherAction() {
+        if (System.console() == null) {
+            return super.runLauncherAction();
+        }
+
+        String pager = System.getenv("RUBY_PAGER");
+        if (pager == null) {
+            pager = System.getenv("PAGER");
+
+            if (pager == null) {
+                return super.runLauncherAction();
+            }
+        }
+
+        pager = pager.strip();
+        if (pager.length() == 0) {
+            return super.runLauncherAction();
+        }
+
+        try {
+            Process process = new ProcessBuilder(pager)
+                    .redirectOutput(Redirect.INHERIT)
+                    .redirectErrorStream(true)
+                    .start();
+            PrintStream out = new PrintStream(process.getOutputStream());
+
+            setOutput(out);
+            boolean code = super.runLauncherAction();
+
+            out.flush();
+            out.close();
+            process.waitFor();
+
+            return code;
+        } catch (IOException | InterruptedException e) {
+            throw abort(e);
+        }
+    }
+
     private int runRubyMain(Context.Builder contextBuilder, CommandLineOptions config) {
         if (config.executionAction == ExecutionAction.UNSET) {
             switch (config.defaultExecutionAction) {