From 5a09eb86f17b7949b93724ecb51f1b909ea68592 Mon Sep 17 00:00:00 2001
From: Maximilian Bosch <maximilian@mbosch.me>
Date: Mon, 29 Jun 2020 10:05:44 +0200
Subject: [PATCH] nix/build: add `--rebuild` option

Occasionally, `nix-build --check` is fairly helpful and I'd like to be
able to use this feature for flakes that need to be built with `nix
build` as well.
---
 src/nix/build.cc        | 9 ++++++++-
 src/nix/command.hh      | 3 ++-
 src/nix/installables.cc | 4 ++--
 3 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/src/nix/build.cc b/src/nix/build.cc
index 0f7e0e123..bec25d8d8 100644
--- a/src/nix/build.cc
+++ b/src/nix/build.cc
@@ -9,6 +9,7 @@ using namespace nix;
 struct CmdBuild : InstallablesCommand, MixDryRun, MixProfile
 {
     Path outLink = "result";
+    BuildMode buildMode = bmNormal;
 
     CmdBuild()
     {
@@ -26,6 +27,12 @@ struct CmdBuild : InstallablesCommand, MixDryRun, MixProfile
             .description = "do not create a symlink to the build result",
             .handler = {&outLink, Path("")},
         });
+
+        addFlag({
+            .longName = "rebuild",
+            .description = "Rebuild an already built package locally and compare the result to the existing store-paths.",
+            .handler = {&buildMode, bmCheck},
+        });
     }
 
     std::string description() override
@@ -53,7 +60,7 @@ struct CmdBuild : InstallablesCommand, MixDryRun, MixProfile
 
     void run(ref<Store> store) override
     {
-        auto buildables = build(store, dryRun ? Realise::Nothing : Realise::Outputs, installables);
+        auto buildables = build(store, dryRun ? Realise::Nothing : Realise::Outputs, installables, buildMode);
 
         if (dryRun) return;
 
diff --git a/src/nix/command.hh b/src/nix/command.hh
index 856721ebf..bc46a2028 100644
--- a/src/nix/command.hh
+++ b/src/nix/command.hh
@@ -5,6 +5,7 @@
 #include "common-eval-args.hh"
 #include "path.hh"
 #include "flake/lockfile.hh"
+#include "store-api.hh"
 
 #include <optional>
 
@@ -185,7 +186,7 @@ static RegisterCommand registerCommand(const std::string & name)
 }
 
 Buildables build(ref<Store> store, Realise mode,
-    std::vector<std::shared_ptr<Installable>> installables);
+    std::vector<std::shared_ptr<Installable>> installables, BuildMode bMode = bmNormal);
 
 std::set<StorePath> toStorePaths(ref<Store> store,
     Realise mode, OperateOn operateOn,
diff --git a/src/nix/installables.cc b/src/nix/installables.cc
index a13e5a3df..56c62dbfe 100644
--- a/src/nix/installables.cc
+++ b/src/nix/installables.cc
@@ -642,7 +642,7 @@ std::shared_ptr<Installable> SourceExprCommand::parseInstallable(
 }
 
 Buildables build(ref<Store> store, Realise mode,
-    std::vector<std::shared_ptr<Installable>> installables)
+    std::vector<std::shared_ptr<Installable>> installables, BuildMode bMode)
 {
     if (mode == Realise::Nothing)
         settings.readOnlyMode = true;
@@ -668,7 +668,7 @@ Buildables build(ref<Store> store, Realise mode,
     if (mode == Realise::Nothing)
         printMissing(store, pathsToBuild, lvlError);
     else if (mode == Realise::Outputs)
-        store->buildPaths(pathsToBuild);
+        store->buildPaths(pathsToBuild, bMode);
 
     return buildables;
 }