A pattern has emerged of wrapping Expression instances with other
Expressions in order to subtly modify their behavior. A key example of
this is in ext/dynblock, where wrap an expression in order to introduce
our additional iteration variable for expressions in dynamic blocks.
Rather than having each wrapper expression implement wrapping
implementations for our various syntax-level-analysis functions (like
ExprList and AbsTraversalForExpr), instead we define a standard mechanism
to unwrap expressions back to the lowest-level object -- usually an AST
node -- and then use this in all of our analyses that look at the
expression's structure rather than its value.
For applications already using hcldec, a decoder specification can be used
to automatically drive the recursive variable detection walk that begins
with WalkForEachVariables, allowing all "for_each" and "labels" variables
in a recursive block structure to be detected in a single call.
The previous ForEachVariables method was flawed because it didn't have
enough information to properly analyze child blocks. Since the core HCL
API requires a schema for any body analysis, and since a schema only
describes one level of configuration structure at a time, we must require
callers to drive a recursive walk through their nested block structure so
that the correct schema can be provided at each level.
This API is rather more complex than is ideal, but is the best we can do
with the HCL Body API as currently defined, and it's currently defined
that way in order to properly support ambiguous syntaxes like JSON.
This extension allows an application to support dynamic generation of
child blocks based on expressions in certain contexts. This is done using
a new block type called "dynamic", which contains an iteration value
(which must be a collection) and a specification of how to construct a
child block for each element of that collection.
This is a super-invasive update since the "zcl" package in particular
is referenced all over.
There are probably still a few zcl references hanging around in comments,
etc but this takes care of most of it.
The main "zcl" package requires a bit more care because of how many
callers it has and because of its two subpackages, so we'll take care
of that one separately.
This package implements a language extension that allows configuration
authors to include the content of another file into a body, using syntax
like this:
include {
path = "./foo.zcl"
}
This is implemented as a transform.Transformer so that it can be used
as part of a transform chain when decoding nested block structures to
allow includes at any arbitrary point.
This capability is not built into the language because certain
applications will offer higher-level constructs for connecting multiple
separate config files, which may e.g. have a separate evaluation scope
for each file, etc.
This utility is intended to support the extension packages that are
siblings of this package, along with third-party extensions, by providing
a way to transform bodies in arbitrary ways.
The "Deep" function then provides a means to apply a particular transform
recursively to a nested block tree, allowing a particular extension to
be supported at arbitrary nesting levels.
This functionality is provided in terms of the standard zcl.Body
interface, so that transform results can be used with any code that
operates generically on bodies. This includes the zcldec and gozcl
packages, so files with extensions can still be decoded in the usual
way.
This package provides helper function that looks in a given body for
blocks that define functions, returning a function map suitable for use
in a zcl.EvalContext.
These will provide additional language features that are implemented in
terms of the basic zcl functionality, so that applications can opt-in to
some more-dynamic behavior if desired.
The general pattern here will be to provide a function that
partially-decodes a given zcl.Body to look for certain block types and
then returns its result along with a zcl.Body representing the remaining,
as-yet-unprocessed content.
