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* When something goes wrong in the evaluation of a Nix expression,

Browse source 
print a nice backtrace of the stack, rather than vomiting a gigantic
  (and useless) aterm on the screen.  Example:

    error: while evaluating file `.../pkgs/system/test.nix':
    while evaluating attribute `subversion' at `.../pkgs/system/all-packages-generic.nix', line 533:
    while evaluating function at `.../pkgs/applications/version-management/subversion/default.nix', line 1:
    assertion failed at `.../pkgs/applications/version-management/subversion/default.nix', line 13

  Since the Nix expression language is lazy, the trace may be
  misleading.  The purpose is to provide a hint as to the location of
  the problem.
This commit is contained in:
Eelco Dolstra 2004-04-05 22:27:41 +00:00
parent a520b1cbc3
commit 59b94ee18a
8 changed files with 201 additions and 90 deletions
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86
src/libexpr/eval.cc
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@ -77,16 +77,16 @@ static Expr substArgs(Expr body, ATermList formals, Expr arg)
Expr key = *i;
Expr cur = subs.get(key);
if (!cur)
throw badTerm(format("function has no formal argument `%1%'")
% aterm2String(key), arg);
throw Error(format("unexpected function argument `%1%'")
% aterm2String(key));
subs.set(key, args.get(key));
}
/* Check that all arguments are defined. */
for (ATermIterator i(subs.keys()); i; ++i)
if (subs.get(*i) == undefined)
throw badTerm(format("formal argument `%1%' missing")
% aterm2String(*i), arg);
throw Error(format("required function argument `%1%' missing")
% aterm2String(*i));
return substitute(subs, body);
}
@ -119,16 +119,18 @@ ATerm expandRec(ATerm e, ATermList rbnds, ATermList nrbnds)
/* Create the non-recursive set. */
ATermMap as;
for (ATermIterator i(rbnds); i; ++i) {
if (!(atMatch(m, *i) >> "Bind" >> name >> e2))
ATerm pos;
if (!(atMatch(m, *i) >> "Bind" >> name >> e2 >> pos))
abort(); /* can't happen */
as.set(name, substitute(subs, e2));
as.set(name, ATmake("(<term>, <term>)", substitute(subs, e2), pos));
}
/* Copy the non-recursive bindings. !!! inefficient */
for (ATermIterator i(nrbnds); i; ++i) {
if (!(atMatch(m, *i) >> "Bind" >> name >> e2))
ATerm pos;
if (!(atMatch(m, *i) >> "Bind" >> name >> e2 >> pos))
abort(); /* can't happen */
as.set(name, e2);
as.set(name, ATmake("(<term>, <term>)", e2, pos));
}
return makeAttrs(as);
@ -140,8 +142,8 @@ static Expr updateAttrs(Expr e1, Expr e2)
/* Note: e1 and e2 should be in normal form. */
ATermMap attrs;
queryAllAttrs(e1, attrs);
queryAllAttrs(e2, attrs);
queryAllAttrs(e1, attrs, true);
queryAllAttrs(e2, attrs, true);
return makeAttrs(attrs);
}
@ -153,7 +155,7 @@ string evalString(EvalState & state, Expr e)
ATMatcher m;
string s;
if (!(atMatch(m, e) >> "Str" >> s))
throw badTerm("string expected", e);
throw Error("string expected");
return s;
}
@ -164,7 +166,7 @@ Path evalPath(EvalState & state, Expr e)
ATMatcher m;
string s;
if (!(atMatch(m, e) >> "Path" >> s))
throw badTerm("path expected", e);
throw Error("path expected");
return s;
}
@ -175,7 +177,7 @@ bool evalBool(EvalState & state, Expr e)
ATMatcher m;
if (atMatch(m, e) >> "Bool" >> "True") return true;
else if (atMatch(m, e) >> "Bool" >> "False") return false;
else throw badTerm("expecting a boolean", e);
else throw Error("boolean expected");
}
@ -183,7 +185,7 @@ Expr evalExpr2(EvalState & state, Expr e)
{
ATMatcher m;
Expr e1, e2, e3, e4;
ATerm name;
ATerm name, pos;
/* Normal forms. */
string cons;
@ -219,6 +221,7 @@ Expr evalExpr2(EvalState & state, Expr e)
if (atMatch(m, e) >> "Call" >> e1 >> e2) {
ATermList formals;
ATerm pos;
/* Evaluate the left-hand side. */
e1 = evalExpr(state, e1);
@ -229,25 +232,42 @@ Expr evalExpr2(EvalState & state, Expr e)
if (primOp) return primOp(state, e2); else abort();
}
else if (atMatch(m, e1) >> "Function" >> formals >> e4)
return evalExpr(state,
substArgs(e4, formals, evalExpr(state, e2)));
else if (atMatch(m, e1) >> "Function1" >> name >> e4) {
ATermMap subs;
subs.set(name, e2);
return evalExpr(state, substitute(subs, e4));
else if (atMatch(m, e1) >> "Function" >> formals >> e4 >> pos) {
e2 = evalExpr(state, e2);
try {
return evalExpr(state, substArgs(e4, formals, e2));
} catch (Error & e) {
throw Error(format("while evaluating function at %1%:\n%2%")
% showPos(pos) % e.msg());
}
}
else throw badTerm("expecting a function or primop", e1);
else if (atMatch(m, e1) >> "Function1" >> name >> e4 >> pos) {
try {
ATermMap subs;
subs.set(name, e2);
return evalExpr(state, substitute(subs, e4));
} catch (Error & e) {
throw Error(format("while evaluating function at %1%:\n%2%")
% showPos(pos) % e.msg());
}
}
else throw Error("function or primop expected in function call");
}
/* Attribute selection. */
string s1;
if (atMatch(m, e) >> "Select" >> e1 >> s1) {
Expr a = queryAttr(evalExpr(state, e1), s1);
if (!a) throw badTerm(format("missing attribute `%1%'") % s1, e);
return evalExpr(state, a);
ATerm pos;
Expr a = queryAttr(evalExpr(state, e1), s1, pos);
if (!a) throw Error(format("attribute `%1%' missing") % s1);
try {
return evalExpr(state, a);
} catch (Error & e) {
throw Error(format("while evaluating attribute `%1%' at %2%:\n%3%")
% s1 % showPos(pos) % e.msg());
}
}
/* Mutually recursive sets. */
@ -264,8 +284,9 @@ Expr evalExpr2(EvalState & state, Expr e)
}
/* Assertions. */
if (atMatch(m, e) >> "Assert" >> e1 >> e2) {
if (!evalBool(state, e1)) throw badTerm("guard failed", e);
if (atMatch(m, e) >> "Assert" >> e1 >> e2 >> pos) {
if (!evalBool(state, e1))
throw Error(format("assertion failed at %1%") % showPos(pos));
return evalExpr(state, e2);
}
@ -323,7 +344,7 @@ Expr evalExpr(EvalState & state, Expr e)
Expr nf = state.normalForms.get(e);
if (nf) {
if (nf == state.blackHole)
throw badTerm("infinite recursion", e);
throw Error("infinite recursion encountered");
state.nrCached++;
return nf;
}
@ -340,7 +361,12 @@ Expr evalFile(EvalState & state, const Path & path)
{
startNest(nest, lvlTalkative, format("evaluating file `%1%'") % path);
Expr e = parseExprFromFile(state, path);
return evalExpr(state, e);
try {
return evalExpr(state, e);
} catch (Error & e) {
throw Error(format("while evaluating file `%1%':\n%2%")
% path % e.msg());
}
}