From 8d51c908729519d11ca7c05327e582e74d8a9ea1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=B6rg=20Thalheim?= <joerg@thalheim.io>
Date: Tue, 26 Nov 2024 07:07:31 +0100
Subject: [PATCH] more readable errors if symlinks cannot be created

Before:

filesystem error: cannot create symlink: Permission denied [/nix/store/1s2p3a4rs172336hj2l8n20nz74hf71j-nix-eval-jobs-2.24.1.drv] [/1s2p3a4rs172336hj2l8n20nz74hf71j-nix-eval-jobs-2.24.1.drv.tmp-2772352-1316231068]

Now:

creating symlink '/wfxz2q489c811n08cdqj7ywxm3n4z6m5-nix-eval-jobs-2.24.1.drv.tmp-2971297-324653080' -> '/nix/store/wfxz2q489c811n08cdqj7ywxm3n4z6m5-nix-eval-jobs-2.24.1.drv': Permission denied

(cherry picked from commit 5b8728d393dd1c9bbbf6737500669853da7de1b3)

# Conflicts:
#	src/nix/flake.cc
---
 src/libutil/file-system.cc | 16 +++++++++++++---
 src/libutil/file-system.hh |  2 --
 src/nix/flake.cc           |  2 +-
 3 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/src/libutil/file-system.cc b/src/libutil/file-system.cc
index fd51d7d3cbd..9f0a0d1c669 100644
--- a/src/libutil/file-system.cc
+++ b/src/libutil/file-system.cc
@@ -602,7 +602,11 @@ std::pair<AutoCloseFD, Path> createTempFile(const Path & prefix)
 
 void createSymlink(const Path & target, const Path & link)
 {
-    fs::create_symlink(target, link);
+    try {
+        fs::create_symlink(target, link);
+    } catch (fs::filesystem_error & e) {
+        throw SysError("creating symlink '%1%' -> '%2%'", link, target);
+    }
 }
 
 void replaceSymlink(const fs::path & target, const fs::path & link)
@@ -615,10 +619,16 @@ void replaceSymlink(const fs::path & target, const fs::path & link)
             fs::create_symlink(target, tmp);
         } catch (fs::filesystem_error & e) {
             if (e.code() == std::errc::file_exists) continue;
-            throw;
+            throw SysError("creating symlink '%1%' -> '%2%'", tmp, target);
+        }
+
+        try {
+            fs::rename(tmp, link);
+        } catch (fs::filesystem_error & e) {
+            if (e.code() == std::errc::file_exists) continue;
+            throw SysError("renaming '%1%' to '%2%'", tmp, link);
         }
 
-        fs::rename(tmp, link);
 
         break;
     }
diff --git a/src/libutil/file-system.hh b/src/libutil/file-system.hh
index eb3e4ec6630..e542f1dfc6e 100644
--- a/src/libutil/file-system.hh
+++ b/src/libutil/file-system.hh
@@ -250,8 +250,6 @@ void setWriteTime(const std::filesystem::path & path, const struct stat & st);
 /**
  * Create a symlink.
  *
- * In the process of being deprecated for
- * `std::filesystem::create_symlink`.
  */
 void createSymlink(const Path & target, const Path & link);
 
diff --git a/src/nix/flake.cc b/src/nix/flake.cc
index 3a54763a199..17637f50d9a 100644
--- a/src/nix/flake.cc
+++ b/src/nix/flake.cc
@@ -941,7 +941,7 @@ struct CmdFlakeInitCommon : virtual Args, EvalCommand
                         }
                         continue;
                     } else
-                          fs::create_symlink(target, to2);
+                        createSymlink(target, to2);
                 }
                 else
                     throw Error("file '%s' has unsupported type", from2);