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authorEelco Dolstra <edolstra@gmail.com>2018-01-16T17·50+0100
committerEelco Dolstra <edolstra@gmail.com>2018-01-16T18·23+0100
commitd4dcffd64349bb52ad5f1b184bee5cc7c2be73b4 (patch)
treef43f027df22b6421bf83d4622c883c3ebc9f846d /src/libutil
parent23fa7e3606a2bee6e3622a61f07e66bdda9b5304 (diff)
Add pure evaluation mode
In this mode, the following restrictions apply:

* The builtins currentTime, currentSystem and storePath throw an
  error.

* $NIX_PATH and -I are ignored.

* fetchGit and fetchMercurial require a revision hash.

* fetchurl and fetchTarball require a sha256 attribute.

* No file system access is allowed outside of the paths returned by
  fetch{Git,Mercurial,url,Tarball}. Thus 'nix build -f ./foo.nix' is
  not allowed.

Thus, the evaluation result is completely reproducible from the
command line arguments. E.g.

  nix build --pure-eval '(
    let
      nix = fetchGit { url = https://github.com/NixOS/nixpkgs.git; rev = "9c927de4b179a6dd210dd88d34bda8af4b575680"; };
      nixpkgs = fetchGit { url = https://github.com/NixOS/nixpkgs.git; ref = "release-17.09"; rev = "66b4de79e3841530e6d9c6baf98702aa1f7124e4"; };
    in (import (nix + "/release.nix") { inherit nix nixpkgs; }).build.x86_64-linux
  )'

The goal is to enable completely reproducible and traceable
evaluation. For example, a NixOS configuration could be fully
described by a single Git commit hash. 'nixos-rebuild' would do
something like

  nix build --pure-eval '(
    (import (fetchGit { url = file:///my-nixos-config; rev = "..."; })).system
  ')

where the Git repository /my-nixos-config would use further fetchGit
calls or Git externals to fetch Nixpkgs and whatever other
dependencies it has. Either way, the commit hash would uniquely
identify the NixOS configuration and allow it to reproduced.
Diffstat (limited to 'src/libutil')
-rw-r--r--src/libutil/util.cc6
-rw-r--r--src/libutil/util.hh6
2 files changed, 10 insertions, 2 deletions
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index 197df0c44aa0..272997397794 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -192,6 +192,12 @@ bool isInDir(const Path & path, const Path & dir)
 }
 
 
+bool isDirOrInDir(const Path & path, const Path & dir)
+{
+    return path == dir or isInDir(path, dir);
+}
+
+
 struct stat lstat(const Path & path)
 {
     struct stat st;
diff --git a/src/libutil/util.hh b/src/libutil/util.hh
index a3494e09b09b..75eb9751524e 100644
--- a/src/libutil/util.hh
+++ b/src/libutil/util.hh
@@ -53,10 +53,12 @@ Path dirOf(const Path & path);
    following the final `/'. */
 string baseNameOf(const Path & path);
 
-/* Check whether a given path is a descendant of the given
-   directory. */
+/* Check whether 'path' is a descendant of 'dir'. */
 bool isInDir(const Path & path, const Path & dir);
 
+/* Check whether 'path' is equal to 'dir' or a descendant of 'dir'. */
+bool isDirOrInDir(const Path & path, const Path & dir);
+
 /* Get status of `path'. */
 struct stat lstat(const Path & path);