From 136a613cce6e119ba5e0a66767c041ce58f7e8c5 Mon Sep 17 00:00:00 2001
From: Guillaume Girol <symphorien+git@xlumurb.eu>
Date: Sun, 25 Jul 2021 12:00:00 +0000
Subject: [PATCH] nix-channel: use nix-env -i --remove-all to upgrade

Fixes #4110
---
 src/nix-channel/nix-channel.cc | 54 ++++++++++++++++++----------------
 1 file changed, 29 insertions(+), 25 deletions(-)

diff --git a/src/nix-channel/nix-channel.cc b/src/nix-channel/nix-channel.cc
index 3272c6125..eae15885a 100755
--- a/src/nix-channel/nix-channel.cc
+++ b/src/nix-channel/nix-channel.cc
@@ -88,15 +88,6 @@ static void update(const StringSet & channelNames)
     for (const auto & channel : channels) {
         auto name = channel.first;
         auto url = channel.second;
-        if (!(channelNames.empty() || channelNames.count(name)))
-            continue;
-
-        // We want to download the url to a file to see if it's a tarball while also checking if we
-        // got redirected in the process, so that we can grab the various parts of a nix channel
-        // definition from a consistent location if the redirect changes mid-download.
-        auto result = fetchers::downloadFile(store, url, std::string(baseNameOf(url)), false);
-        auto filename = store->toRealPath(result.storePath);
-        url = result.effectiveUrl;
 
         // If the URL contains a version number, append it to the name
         // attribute (so that "nix-env -q" on the channels profile
@@ -109,30 +100,43 @@ static void update(const StringSet & channelNames)
 
         std::string extraAttrs;
 
-        bool unpacked = false;
-        if (std::regex_search(filename, std::regex("\\.tar\\.(gz|bz2|xz)$"))) {
-            runProgram(settings.nixBinDir + "/nix-build", false, { "--no-out-link", "--expr", "import " + unpackChannelPath +
-                        "{ name = \"" + cname + "\"; channelName = \"" + name + "\"; src = builtins.storePath \"" + filename + "\"; }" });
-            unpacked = true;
-        }
+        if (!(channelNames.empty() || channelNames.count(name))) {
+            // no need to update this channel, reuse the existing store path
+            Path symlink = profile + "/" + name;
+            Path storepath = dirOf(readLink(symlink));
+            exprs.push_back("f: rec { name = \"" + cname + "\"; type = \"derivation\"; outputs = [\"out\"]; system = \"builtin\"; outPath = builtins.storePath \"" + storepath + "\"; out = { inherit outPath; };}");
+        } else {
+            // We want to download the url to a file to see if it's a tarball while also checking if we
+            // got redirected in the process, so that we can grab the various parts of a nix channel
+            // definition from a consistent location if the redirect changes mid-download.
+            auto result = fetchers::downloadFile(store, url, std::string(baseNameOf(url)), false);
+            auto filename = store->toRealPath(result.storePath);
+            url = result.effectiveUrl;
 
-        if (!unpacked) {
-            // Download the channel tarball.
-            try {
-                filename = store->toRealPath(fetchers::downloadFile(store, url + "/nixexprs.tar.xz", "nixexprs.tar.xz", false).storePath);
-            } catch (FileTransferError & e) {
-                filename = store->toRealPath(fetchers::downloadFile(store, url + "/nixexprs.tar.bz2", "nixexprs.tar.bz2", false).storePath);
+            bool unpacked = false;
+            if (std::regex_search(filename, std::regex("\\.tar\\.(gz|bz2|xz)$"))) {
+                runProgram(settings.nixBinDir + "/nix-build", false, { "--no-out-link", "--expr", "import " + unpackChannelPath +
+                            "{ name = \"" + cname + "\"; channelName = \"" + name + "\"; src = builtins.storePath \"" + filename + "\"; }" });
+                unpacked = true;
             }
-        }
 
-        // Regardless of where it came from, add the expression representing this channel to accumulated expression
-        exprs.push_back("f: f { name = \"" + cname + "\"; channelName = \"" + name + "\"; src = builtins.storePath \"" + filename + "\"; " + extraAttrs + " }");
+            if (!unpacked) {
+                // Download the channel tarball.
+                try {
+                    filename = store->toRealPath(fetchers::downloadFile(store, url + "/nixexprs.tar.xz", "nixexprs.tar.xz", false).storePath);
+                } catch (FileTransferError & e) {
+                    filename = store->toRealPath(fetchers::downloadFile(store, url + "/nixexprs.tar.bz2", "nixexprs.tar.bz2", false).storePath);
+                }
+            }
+            // Regardless of where it came from, add the expression representing this channel to accumulated expression
+            exprs.push_back("f: f { name = \"" + cname + "\"; channelName = \"" + name + "\"; src = builtins.storePath \"" + filename + "\"; " + extraAttrs + " }");
+        }
     }
 
     // Unpack the channel tarballs into the Nix store and install them
     // into the channels profile.
     std::cerr << "unpacking channels...\n";
-    Strings envArgs{ "--profile", profile, "--file", unpackChannelPath, "--install", "--from-expression" };
+    Strings envArgs{ "--profile", profile, "--file", unpackChannelPath, "--install", "--remove-all", "--from-expression" };
     for (auto & expr : exprs)
         envArgs.push_back(std::move(expr));
     envArgs.push_back("--quiet");