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Optionally ignore null-valued derivation attributes

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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.
This commit is contained in:
Eelco Dolstra 2012-11-27 15:01:32 +01:00
parent 8b8ee53bc7
commit 6c98e6a5de
3 changed files with 24 additions and 11 deletions
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32
src/libexpr/primops.cc
View file

@ -310,16 +310,22 @@ static void prim_derivationStrict(EvalState & state, Value * * args, Value & v)
throw EvalError("required attribute `name' missing");
string drvName;
Pos & posDrvName(*attr->pos);
try {
try {
drvName = state.forceStringNoCtx(*attr->value);
} catch (Error & e) {
e.addPrefix(format("while evaluating the derivation attribute `name' at %1%:\n") % posDrvName);
throw;
}
/* Check whether null attributes should be ignored. */
bool ignoreNulls = false;
attr = args[0]->attrs->find(state.sIgnoreNulls);
if (attr != args[0]->attrs->end())
ignoreNulls = state.forceBool(*attr->value);
/* Build the derivation expression by processing the attributes. */
Derivation drv;
PathSet context;
string outputHash, outputHashAlgo;
@ -329,11 +335,17 @@ static void prim_derivationStrict(EvalState & state, Value * * args, Value & v)
outputs.insert("out");
foreach (Bindings::iterator, i, *args[0]->attrs) {
if (i->name == state.sIgnoreNulls) continue;
string key = i->name;
startNest(nest, lvlVomit, format("processing attribute `%1%'") % key);
try {
if (ignoreNulls) {
state.forceValue(*i->value);
if (i->value->type == tNull) continue;
}
/* The `args' attribute is special: it supplies the
command-line arguments to the builder. */
if (key == "args") {
@ -358,7 +370,7 @@ static void prim_derivationStrict(EvalState & state, Value * * args, Value & v)
else if (key == "outputHash") outputHash = s;
else if (key == "outputHashAlgo") outputHashAlgo = s;
else if (key == "outputHashMode") {
if (s == "recursive") outputHashRecursive = true;
if (s == "recursive") outputHashRecursive = true;
else if (s == "flat") outputHashRecursive = false;
else throw EvalError(format("invalid value `%1%' for `outputHashMode' attribute") % s);
}
@ -390,13 +402,13 @@ static void prim_derivationStrict(EvalState & state, Value * * args, Value & v)
throw;
}
}
/* Everything in the context of the strings in the derivation
attributes should be added as dependencies of the resulting
derivation. */
foreach (PathSet::iterator, i, context) {
Path path = *i;
/* Paths marked with `=' denote that the path of a derivation
is explicitly passed to the builder. Since that allows the
builder to gain access to every path in the dependency
@ -433,7 +445,7 @@ static void prim_derivationStrict(EvalState & state, Value * * args, Value & v)
else
drv.inputSrcs.insert(path);
}
/* Do we have all required attributes? */
if (drv.builder == "")
throw EvalError("required attribute `builder' missing");
@ -450,14 +462,14 @@ static void prim_derivationStrict(EvalState & state, Value * * args, Value & v)
/* Handle fixed-output derivations. */
if (outputs.size() != 1 || *(outputs.begin()) != "out")
throw Error("multiple outputs are not supported in fixed-output derivations");
HashType ht = parseHashType(outputHashAlgo);
if (ht == htUnknown)
throw EvalError(format("unknown hash algorithm `%1%'") % outputHashAlgo);
Hash h = parseHash16or32(ht, outputHash);
outputHash = printHash(h);
if (outputHashRecursive) outputHashAlgo = "r:" + outputHashAlgo;
Path outPath = makeFixedOutputPath(outputHashRecursive, ht, h, drvName);
drv.env["out"] = outPath;
drv.outputs["out"] = DerivationOutput(outPath, outputHashAlgo, outputHash);
@ -477,7 +489,7 @@ static void prim_derivationStrict(EvalState & state, Value * * args, Value & v)
/* Use the masked derivation expression to compute the output
path. */
Hash h = hashDerivationModulo(*store, drv);
foreach (DerivationOutputs::iterator, i, drv.outputs)
if (i->second.path == "") {
Path outPath = makeOutputPath(i->first, h, drvName);