* Big cleanup of the semantics of paths, strings, contexts, string

  concatenation and string coercion.  This was a big mess (see
  e.g. NIX-67).  Contexts are now folded into strings, so that they
  don't cause evaluation errors when they're not expected.  The
  semantics of paths has been clarified (see nixexpr-ast.def).
  toString() and coerceToString() have been merged.

  Semantic change: paths are now copied to the store when they're in a
  concatenation (and in most other situations - that's the
  formalisation of the meaning of a path).  So

    "foo " + ./bla

  evaluates to "foo /nix/store/hash...-bla", not "foo
  /path/to/current-dir/bla".  This prevents accidental impurities, and
  is more consistent with the treatment of derivation outputs, e.g.,
  `"foo " + bla' where `bla' is a derivation.  (Here `bla' would be
  replaced by the output path of `bla'.)

1 files changed, 16 insertions, 7 deletions

diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index a7f4e69437..323a828734 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -60,17 +60,26 @@ Expr strictEvalExpr(EvalState & state, Expr e,
     bool canonicalise = false);
 
 /* Specific results. */
-string evalString(EvalState & state, Expr e);
-Path evalPath(EvalState & state, Expr e);
+string evalString(EvalState & state, Expr e, PathSet & context);
+string evalStringNoCtx(EvalState & state, Expr e);
 int evalInt(EvalState & state, Expr e);
 bool evalBool(EvalState & state, Expr e);
 ATermList evalList(EvalState & state, Expr e);
-ATerm coerceToString(Expr e);
 
-/* Contexts. */
-string coerceToStringWithContext(EvalState & state,
-    ATermList & context, Expr e, bool & isPath);
-Expr wrapInContext(ATermList context, Expr e);
+/* Flatten nested lists into a single list (or expand a singleton into
+   a list). */
+ATermList flattenList(EvalState & state, Expr e);
+
+/* String coercion.  Converts strings, paths and derivations to a
+   string.  If `coerceMore' is set, also converts nulls, integers,
+   booleans and lists to a string. */
+string coerceToString(EvalState & state, Expr e, PathSet & context,
+    bool coerceMore = false, bool copyToStore = true);
+
+/* Path coercion.  Converts strings, paths and derivations to a path.
+   The result is guaranteed to be an canonicalised, absolute path.
+   Nothing is copied to the store. */
+Path coerceToPath(EvalState & state, Expr e, PathSet & context);
 
 /* Automatically call a function for which each argument has a default
    value or has a binding in the `args' map.  Note: result is a call,