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* In the ‘?’ operator, allow attribute paths. For instance, you can

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write ‘attrs ? a.b’ to test whether ‘attrs’ has an attribute ‘a’
  containing an attribute ‘b’.  This is more convenient than ‘attrs ?
  a && attrs.a ? b’.

  Slight change in the semantics: it's no longer an error if the
  left-hand side of ‘?’ is not an attribute set.  In that case it just
  returns false.  So, ‘null ? foo’ no longer throws an error.
This commit is contained in:
Eelco Dolstra 2011-07-06 10:58:17 +00:00
parent 34f4b91820
commit 5637037802
4 changed files with 47 additions and 24 deletions
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26
src/libexpr/parser.y
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@ -61,18 +61,7 @@ using namespace nix;
namespace nix {
static string showAttrPath(const vector<Symbol> & attrPath)
{
string s;
foreach (vector<Symbol>::const_iterator, i, attrPath) {
if (!s.empty()) s += '.';
s += *i;
}
return s;
}
static void dupAttr(const vector<Symbol> & attrPath, const Pos & pos, const Pos & prevPos)
static void dupAttr(const AttrPath & attrPath, const Pos & pos, const Pos & prevPos)
{
throw ParseError(format("attribute `%1%' at %2% already defined at %3%")
% showAttrPath(attrPath) % pos % prevPos);
@ -81,17 +70,17 @@ static void dupAttr(const vector<Symbol> & attrPath, const Pos & pos, const Pos
static void dupAttr(Symbol attr, const Pos & pos, const Pos & prevPos)
{
vector<Symbol> attrPath; attrPath.push_back(attr);
AttrPath attrPath; attrPath.push_back(attr);
throw ParseError(format("attribute `%1%' at %2% already defined at %3%")
% showAttrPath(attrPath) % pos % prevPos);
}
static void addAttr(ExprAttrs * attrs, const vector<Symbol> & attrPath,
static void addAttr(ExprAttrs * attrs, AttrPath & attrPath,
Expr * e, const Pos & pos)
{
unsigned int n = 0;
foreach (vector<Symbol>::const_iterator, i, attrPath) {
foreach (AttrPath::const_iterator, i, attrPath) {
n++;
ExprAttrs::AttrDefs::iterator j = attrs->attrs.find(*i);
if (j != attrs->attrs.end()) {
@ -238,6 +227,7 @@ void yyerror(YYLTYPE * loc, yyscan_t scanner, ParseData * data, const char * err
%}
%union {
// !!! We're probably leaking stuff here.
nix::Expr * e;
nix::ExprList * list;
nix::ExprAttrs * attrs;
@ -317,7 +307,7 @@ expr_op
| expr_op OR expr_op { $$ = new ExprOpOr($1, $3); }
| expr_op IMPL expr_op { $$ = new ExprOpImpl($1, $3); }
| expr_op UPDATE expr_op { $$ = new ExprOpUpdate($1, $3); }
| expr_op '?' ID { $$ = new ExprOpHasAttr($1, data->symbols.create($3)); }
| expr_op '?' attrpath { $$ = new ExprOpHasAttr($1, *$3); }
| expr_op '+' expr_op
{ vector<Expr *> * l = new vector<Expr *>;
l->push_back($1);
@ -382,7 +372,7 @@ binds
: binds attrpath '=' expr ';' { $$ = $1; addAttr($$, *$2, $4, makeCurPos(@2, data)); }
| binds INHERIT ids ';'
{ $$ = $1;
foreach (vector<Symbol>::iterator, i, *$3) {
foreach (AttrPath::iterator, i, *$3) {
if ($$->attrs.find(*i) != $$->attrs.end())
dupAttr(*i, makeCurPos(@3, data), $$->attrs[*i].pos);
Pos pos = makeCurPos(@3, data);
@ -392,7 +382,7 @@ binds
| binds INHERIT '(' expr ')' ids ';'
{ $$ = $1;
/* !!! Should ensure sharing of the expression in $4. */
foreach (vector<Symbol>::iterator, i, *$6) {
foreach (AttrPath::iterator, i, *$6) {
if ($$->attrs.find(*i) != $$->attrs.end())
dupAttr(*i, makeCurPos(@6, data), $$->attrs[*i].pos);
$$->attrs[*i] = ExprAttrs::AttrDef(new ExprSelect($4, *i), makeCurPos(@6, data));