diff options
| -rw-r--r-- | src/libexpr/eval.cc | 26 | ||||
| -rw-r--r-- | src/libexpr/nixexpr-ast.def | 1 |
2 files changed, 25 insertions, 2 deletions
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc index e79d42504d0a..3da9cbc4d57e 100644 --- a/src/libexpr/eval.cc +++ b/src/libexpr/eval.cc @@ -170,16 +170,18 @@ static Expr substArgs(EvalState & state, to attributes substituted with selection expressions on the original set. E.g., e = `rec {x = f x y; y = x;}' becomes `{x = f (e.x) (e.y); y = e.x;}'. */ -LocalNoInline(ATerm expandRec(ATerm e, ATermList rbnds, ATermList nrbnds)) +LocalNoInline(ATerm expandRec(EvalState & state, ATerm e, ATermList rbnds, ATermList nrbnds)) { ATerm name; Expr e2; Pos pos; + Expr eOverrides = 0; /* Create the substitution list. */ ATermMap subs(ATgetLength(rbnds) + ATgetLength(nrbnds)); for (ATermIterator i(rbnds); i; ++i) { if (!matchBind(*i, name, e2, pos)) abort(); /* can't happen */ + if (name == sOverrides) eOverrides = e2; subs.set(name, makeSelect(e, name)); } for (ATermIterator i(nrbnds); i; ++i) { @@ -187,6 +189,22 @@ LocalNoInline(ATerm expandRec(ATerm e, ATermList rbnds, ATermList nrbnds)) subs.set(name, e2); } + /* If the rec contains an attribute called `__overrides', then + evaluate it, and add the attributes in that set to the rec. + This allows overriding of recursive attributes, which is + otherwise not possible. (You can use the // operator to + replace an attribute, but other attributes in the rec will + still reference the original value, because that value has been + substituted into the bodies of the other attributes. Hence we + need __overrides.) */ + ATermMap overrides; + if (eOverrides) { + eOverrides = evalExpr(state, eOverrides); + queryAllAttrs(overrides, overrides, false); + foreach (ATermMap::const_iterator, i, overrides) + subs.set(i->key, i->value); + } + Substitution subs_(0, &subs); /* Create the non-recursive set. */ @@ -196,6 +214,10 @@ LocalNoInline(ATerm expandRec(ATerm e, ATermList rbnds, ATermList nrbnds)) as.set(name, makeAttrRHS(substitute(subs_, e2), pos)); } + if (eOverrides) + foreach (ATermMap::const_iterator, i, overrides) + as.set(i->key, makeAttrRHS(i->value, makeNoPos())); + /* Copy the non-recursive bindings. !!! inefficient */ for (ATermIterator i(nrbnds); i; ++i) { if (!matchBind(*i, name, e2, pos)) abort(); /* can't happen */ @@ -667,7 +689,7 @@ Expr evalExpr2(EvalState & state, Expr e) /* Mutually recursive sets. */ ATermList rbnds, nrbnds; if (matchRec(e, rbnds, nrbnds)) - return expandRec(e, rbnds, nrbnds); + return expandRec(state, e, rbnds, nrbnds); /* Conditionals. */ if (matchIf(e, e1, e2, e3)) diff --git a/src/libexpr/nixexpr-ast.def b/src/libexpr/nixexpr-ast.def index ab749b3dbe84..ba8162984156 100644 --- a/src/libexpr/nixexpr-ast.def +++ b/src/libexpr/nixexpr-ast.def @@ -93,3 +93,4 @@ AttrRHS | Expr Pos | ATerm | eTrue = makeBool(makeTrue()) eFalse = makeBool(makeFalse()) +sOverrides = toATerm("__overrides") |