From 61216d32e1c0973424d549c9f3065426b51015c9 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Wed, 13 Jan 2021 23:27:39 +0100
Subject: [PATCH] Add 'nix store repair' command

---
 src/libstore/local-store.hh |  4 +---
 src/libstore/store-api.hh   |  5 +++++
 src/nix-store/nix-store.cc  |  2 +-
 src/nix/store-delete.cc     |  1 -
 src/nix/store-repair.cc     | 27 +++++++++++++++++++++++++++
 src/nix/store-repair.md     | 32 ++++++++++++++++++++++++++++++++
 6 files changed, 66 insertions(+), 5 deletions(-)
 create mode 100644 src/nix/store-repair.cc
 create mode 100644 src/nix/store-repair.md

diff --git a/src/libstore/local-store.hh b/src/libstore/local-store.hh
index 6d29c5960..6c7ebac1e 100644
--- a/src/libstore/local-store.hh
+++ b/src/libstore/local-store.hh
@@ -198,9 +198,7 @@ public:
 
     void vacuumDB();
 
-    /* Repair the contents of the given path by redownloading it using
-       a substituter (if available). */
-    void repairPath(const StorePath & path);
+    void repairPath(const StorePath & path) override;
 
     void addSignatures(const StorePath & storePath, const StringSet & sigs) override;
 
diff --git a/src/libstore/store-api.hh b/src/libstore/store-api.hh
index 9bcff08eb..d1b83933a 100644
--- a/src/libstore/store-api.hh
+++ b/src/libstore/store-api.hh
@@ -604,6 +604,11 @@ public:
     virtual ref<FSAccessor> getFSAccessor()
     { unsupported("getFSAccessor"); }
 
+    /* Repair the contents of the given path by redownloading it using
+       a substituter (if available). */
+    virtual void repairPath(const StorePath & path)
+    { unsupported("repairPath"); }
+
     /* Add signatures to the specified store path. The signatures are
        not verified. */
     virtual void addSignatures(const StorePath & storePath, const StringSet & sigs)
diff --git a/src/nix-store/nix-store.cc b/src/nix-store/nix-store.cc
index e43788bc3..b97f684a4 100644
--- a/src/nix-store/nix-store.cc
+++ b/src/nix-store/nix-store.cc
@@ -757,7 +757,7 @@ static void opRepairPath(Strings opFlags, Strings opArgs)
         throw UsageError("no flags expected");
 
     for (auto & i : opArgs)
-        ensureLocalStore()->repairPath(store->followLinksToStorePath(i));
+        store->repairPath(store->followLinksToStorePath(i));
 }
 
 /* Optimise the disk space usage of the Nix store by hard-linking
diff --git a/src/nix/store-delete.cc b/src/nix/store-delete.cc
index 9c8fef191..10245978e 100644
--- a/src/nix/store-delete.cc
+++ b/src/nix/store-delete.cc
@@ -32,7 +32,6 @@ struct CmdStoreDelete : StorePathsCommand
 
     void run(ref<Store> store, std::vector<StorePath> storePaths) override
     {
-
         for (auto & path : storePaths)
             options.pathsToDelete.insert(path);
 
diff --git a/src/nix/store-repair.cc b/src/nix/store-repair.cc
new file mode 100644
index 000000000..1c7a4392e
--- /dev/null
+++ b/src/nix/store-repair.cc
@@ -0,0 +1,27 @@
+#include "command.hh"
+#include "store-api.hh"
+
+using namespace nix;
+
+struct CmdStoreRepair : StorePathsCommand
+{
+    std::string description() override
+    {
+        return "repair store paths";
+    }
+
+    std::string doc() override
+    {
+        return
+          #include "store-repair.md"
+          ;
+    }
+
+    void run(ref<Store> store, std::vector<StorePath> storePaths) override
+    {
+        for (auto & path : storePaths)
+            store->repairPath(path);
+    }
+};
+
+static auto rStoreRepair = registerCommand2<CmdStoreRepair>({"store", "repair"});
diff --git a/src/nix/store-repair.md b/src/nix/store-repair.md
new file mode 100644
index 000000000..92d2205a9
--- /dev/null
+++ b/src/nix/store-repair.md
@@ -0,0 +1,32 @@
+R""(
+
+# Examples
+
+* Repair a store path, after determining that it is corrupt:
+
+  ```console
+  # nix store verify /nix/store/yb5q57zxv6hgqql42d5r8b5k5mcq6kay-hello-2.10
+  path '/nix/store/yb5q57zxv6hgqql42d5r8b5k5mcq6kay-hello-2.10' was
+  modified! expected hash
+  'sha256:1hd5vnh6xjk388gdk841vflicy8qv7qzj2hb7xlyh8lpb43j921l', got
+  'sha256:1a25lf78x5wi6pfkrxalf0n13kdaca0bqmjqnp7wfjza2qz5ssgl'
+
+  # nix store repair /nix/store/yb5q57zxv6hgqql42d5r8b5k5mcq6kay-hello-2.10
+  ```
+
+# Description
+
+This command attempts to "repair" the store paths specified by
+*installables* by redownloading them using the available
+substituters. If no substitutes are available, then repair is not
+possible.
+
+> **Warning**
+>
+> During repair, there is a very small time window during which the old
+> path (if it exists) is moved out of the way and replaced with the new
+> path. If repair is interrupted in between, then the system may be left
+> in a broken state (e.g., if the path contains a critical system
+> component like the GNU C Library).
+
+)""