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#include "attr-path.hh"
#include "nixexpr-ast.hh"
bool isAttrs(EvalState & state, Expr e, ATermMap & attrs)
{
e = evalExpr(state, e);
ATermList dummy;
if (!matchAttrs(e, dummy)) return false;
queryAllAttrs(e, attrs, false);
return true;
}
Expr findAlongAttrPath(EvalState & state, const string & attrPath, Expr e)
{
Strings tokens = tokenizeString(attrPath, ".");
Error attrError =
Error(format("attribute selection path `%1%' does not match expression") % attrPath);
string curPath;
for (Strings::iterator i = tokens.begin(); i != tokens.end(); ++i) {
if (!curPath.empty()) curPath += ".";
curPath += *i;
/* Is *i an index (integer) or a normal attribute name? */
enum { apAttr, apIndex } apType = apAttr;
string attr = *i;
int attrIndex = -1;
if (string2Int(attr, attrIndex)) apType = apIndex;
/* Evaluate the expression. */
e = evalExpr(state, autoCallFunction(evalExpr(state, e), ATermMap(1)));
/* It should evaluate to either an attribute set or an
expression, according to what is specified in the
attrPath. */
if (apType == apAttr) {
ATermMap attrs(128);
if (!isAttrs(state, e, attrs))
throw TypeError(
format("the expression selected by the selection path `%1%' should be an attribute set but is %2%")
% curPath % showType(e));
e = attrs.get(toATerm(attr));
if (!e)
throw Error(format("attribute `%1%' in selection path `%2%' not found") % attr % curPath);
}
else if (apType == apIndex) {
ATermList es;
if (!matchList(e, es))
throw TypeError(
format("the expression selected by the selection path `%1%' should be a list but is %2%")
% curPath % showType(e));
e = ATelementAt(es, attrIndex);
if (!e)
throw Error(format("list index %1% in selection path `%2%' not found") % attrIndex % curPath);
}
}
return e;
}
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