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authorEelco Dolstra <eelco.dolstra@logicblox.com>2012-11-27T14·01+0100
committerEelco Dolstra <eelco.dolstra@logicblox.com>2012-11-27T14·01+0100
commit6c98e6a5dec2bcbc25ddeb2c279aa4a0b274bd6a (patch)
tree2ef5df17cd5fc359c27f96adb3279deb791591a9 /src/libexpr/eval.cc
parent8b8ee53bc73769bb25d967ba259dabc9b23e2e6f (diff)
Optionally ignore null-valued derivation attributes
This allows adding attributes like

  attr = if stdenv.system == "bla" then something else null;

without changing the resulting derivation on non-<bla> platforms.

We once considered adding a special "ignore" value for this purpose,
but using null seems more elegant.
Diffstat (limited to 'src/libexpr/eval.cc')
-rw-r--r--src/libexpr/eval.cc1
1 files changed, 1 insertions, 0 deletions
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 31aaad5485f0..9eb5fc758985 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -139,6 +139,7 @@ EvalState::EvalState()
     , sSystem(symbols.create("system"))
     , sOverrides(symbols.create("__overrides"))
     , sOutputName(symbols.create("outputName"))
+    , sIgnoreNulls(symbols.create("__ignoreNulls"))
     , baseEnv(allocEnv(128))
     , baseEnvDispl(0)
     , staticBaseEnv(false, 0)