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

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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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6
src/libexpr/nixexpr.hh
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@ -52,6 +52,9 @@ private:
ATerm string2ATerm(const string & s);
string aterm2String(ATerm t);
/* Show a position. */
string showPos(ATerm pos);
/* Generic bottomup traversal over ATerms. The traversal first
recursively descends into subterms, and then applies the given term
function to the resulting term. */
@ -63,11 +66,12 @@ ATerm bottomupRewrite(TermFun & f, ATerm e);
/* Query all attributes in an attribute set expression. The
expression must be in normal form. */
void queryAllAttrs(Expr e, ATermMap & attrs);
void queryAllAttrs(Expr e, ATermMap & attrs, bool withPos = false);
/* Query a specific attribute from an attribute set expression. The
expression must be in normal form. */
Expr queryAttr(Expr e, const string & name);
Expr queryAttr(Expr e, const string & name, ATerm & pos);
/* Create an attribute set expression from an Attrs value. */
Expr makeAttrs(const ATermMap & attrs);