From 6ef00a503a62dc5554139804d22968b25ba4bf3f Mon Sep 17 00:00:00 2001
From: Robert Hensing <robert@roberthensing.nl>
Date: Fri, 5 Jul 2024 18:32:34 +0200
Subject: [PATCH] Explain when man is missing

Have you seen this man?

Fixes #10677
---
 src/libmain/shared.cc    | 4 ++++
 tests/functional/misc.sh | 3 +++
 2 files changed, 7 insertions(+)

diff --git a/src/libmain/shared.cc b/src/libmain/shared.cc
index c1c936248..fc55fe3f1 100644
--- a/src/libmain/shared.cc
+++ b/src/libmain/shared.cc
@@ -320,6 +320,10 @@ void showManPage(const std::string & name)
     restoreProcessContext();
     setEnv("MANPATH", settings.nixManDir.c_str());
     execlp("man", "man", name.c_str(), nullptr);
+    if (errno == ENOENT) {
+        // Not SysError because we don't want to suffix the errno, aka No such file or directory.
+        throw Error("The '%1%' command was not found, but it is needed for '%2%' and some other '%3%' commands' help text. Perhaps you could install the '%1%' command?", "man", name.c_str(), "nix-*");
+    }
     throw SysError("command 'man %1%' failed", name.c_str());
 }
 
diff --git a/tests/functional/misc.sh b/tests/functional/misc.sh
index 9eb80ad22..7d63756b7 100755
--- a/tests/functional/misc.sh
+++ b/tests/functional/misc.sh
@@ -13,6 +13,9 @@ source common.sh
 # Can we ask for the version number?
 nix-env --version | grep "$version"
 
+nix_env=$(type -P nix-env)
+(PATH=""; ! $nix_env --help 2>&1 ) | grepQuiet -F "The 'man' command was not found, but it is needed for 'nix-env' and some other 'nix-*' commands' help text. Perhaps you could install the 'man' command?"
+
 # Usage errors.
 expect 1 nix-env --foo 2>&1 | grep "no operation"
 expect 1 nix-env -q --foo 2>&1 | grep "unknown flag"