From 7577d358959b5e1797f441a1f6cb8edf206cb179 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Tue, 11 Jul 2017 23:20:01 +0200
Subject: [PATCH] replaceSymlink(): Handle the case where the temporary file
 already exists

Not really necessary anymore for #849, but still nice to have.

(cherry picked from commit 2965d40612e16388ef2177d2a13d168848c6ca8a)
---
 src/libutil/util.cc | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index 1d6c38d3..62d8efa3 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -431,12 +431,21 @@ void createSymlink(const Path & target, const Path & link)
 
 void replaceSymlink(const Path & target, const Path & link)
 {
-    Path tmp = canonPath(dirOf(link) + "/.new_" + baseNameOf(link));
+    for (unsigned int n = 0; true; n++) {
+        Path tmp = canonPath(fmt("%s/.%d_%s", dirOf(link), n, baseNameOf(link)));
 
-    createSymlink(target, tmp);
+        try {
+            createSymlink(target, tmp);
+        } catch (SysError & e) {
+            if (e.errNo == EEXIST) continue;
+            throw;
+        }
 
-    if (rename(tmp.c_str(), link.c_str()) != 0)
-        throw SysError(format("renaming ‘%1%’ to ‘%2%’") % tmp % link);
+        if (rename(tmp.c_str(), link.c_str()) != 0)
+            throw SysError(format("renaming ‘%1%’ to ‘%2%’") % tmp % link);
+
+        break;
+    }
 }