diff options
Diffstat (limited to 'src/libexpr/nixexpr-ast.def')
| -rw-r--r-- | src/libexpr/nixexpr-ast.def | 32 |
1 files changed, 30 insertions, 2 deletions
diff --git a/src/libexpr/nixexpr-ast.def b/src/libexpr/nixexpr-ast.def index b797fcfc4..fe5fe71b0 100644 --- a/src/libexpr/nixexpr-ast.def +++ b/src/libexpr/nixexpr-ast.def @@ -24,8 +24,37 @@ Call | Expr Expr | Expr | Select | Expr string | Expr | Var | string | Expr | Int | int | Expr | -Str | string | Expr | + +# Strings in the evaluator carry a so-called `context' (the ATermList) +# which is a list of strings representing store paths. This is to +# allow users to write things like +# +# "--with-freetype2-library=" + freetype + "/lib" +# +# where `freetype' is a derivation (or a source to be copied to the +# store). If we just concatenated the strings without keeping track +# of the referenced store paths, then if the string is used as a +# derivation attribute, the derivation will not have the correct +# dependencies in its inputDrvs and inputSrcs. +# +# The semantics of the context is as follows: when a string with +# context C is used as a derivation attribute, then the derivations in +# C will be added to the inputDrvs of the derivation, and the other +# store paths in C will be added to the inputSrcs of the derivations. +# +# For canonicity, the store paths should be in sorted order. +Str | string ATermList | Expr | + +# A path is a reference to a file system object that is to be copied +# to the Nix store when used as a derivation attribute. When it is +# concatenated to a string (i.e., `str + path'), it is also copied and +# the resulting store path is concatenated to the string (with the +# store path in the context). If a string or path is concatenated to +# a path (i.e., `path + str' or `path + path'), the result is a new +# path (if the right-hand side is a string, the context must be +# empty). Path | string | Expr | + List | ATermList | Expr | BlackHole | | Expr | Undefined | | Expr | @@ -36,7 +65,6 @@ Closed | Expr | Expr | Rec | ATermList ATermList | Expr | Bool | ATerm | Expr | Null | | Expr | -Context | ATermList Expr | Expr | Bind | string Expr Pos | ATerm | Bind | string Expr | ATerm | Bind2 |