Merge pull request NixOS#8047 from lovesegfault/always-allow-substitutes

feat: add always-allow-substitutes

doc/manual/src/language/advanced-attributes.md

@@ -270,6 +270,9 @@ Derivations can declare some infrequently used optional attributes.
     useful for very trivial derivations (such as `writeText` in Nixpkgs)
     that are cheaper to build than to substitute from a binary cache.
 
+    You may disable the effects of this attibute by enabling the
+    `always-allow-substitutes` configuration option in Nix.
+
     > **Note**
     >
     > You need to have a builder configured which satisfies the

src/libstore/globals.hh

@@ -262,6 +262,14 @@ public:
           For the exact format and examples, see [the manual chapter on remote builds](../advanced-topics/distributed-builds.md)
         )"};
 
+    Setting<bool> alwaysAllowSubstitutes{
+        this, false, "always-allow-substitutes",
+        R"(
+          If set to `true`, Nix will ignore the `allowSubstitutes` attribute in
+          derivations and always attempt to use available substituters.
+          For more information on `allowSubstitutes`, see [the manual chapter on advanced attributes](../language/advanced-attributes.md).
+        )"};
+
     Setting<bool> buildersUseSubstitutes{
         this, false, "builders-use-substitutes",
         R"(

src/libstore/parsed-derivations.cc

@@ -122,7 +122,7 @@ bool ParsedDerivation::willBuildLocally(Store & localStore) const
 
 bool ParsedDerivation::substitutesAllowed() const
 {
-    return getBoolAttr("allowSubstitutes", true);
+    return settings.alwaysAllowSubstitutes ? true : getBoolAttr("allowSubstitutes", true);
 }
 
 bool ParsedDerivation::useUidRange() const