When helping folks in the community forum, I commonly see questions around
more complex patterns in transforming deep data structures into different
shapes to work with for_each. We have examples of these patterns in the
docs for the functions that they rely on, but they were not previously
very discoverable in the main configuration language documentation
sections.
Here I've moved the "Using Expressions in for_each" subsection on the
Resources page above some of the other sub-sections to hopefully make it
easier to see, and written out in more detail the two specific patterns
that answer a significant number of for_each-related user questions in
the hope that readers will be more likely to realize that the links are
relevant to what their goals.
I also added some more elaboration about the behavior of converting from
list to set in the "Using Sets" subsection, because this feature is often
a user's first encounter with the set data type and I've inferred from
some of the questions I've answered that a number of Terraform users don't
have prior experience with set data types in other languages to draw
assumptions from.
Finally, I added some similar links to the for_each patterns within the
for expression documentation itself, to try to make those examples more
visible to those who might be discovering the documentation in a different
sequence, e.g. by following a deep link shared in an answer to a question
in the community forum.
A very common question since we launched the two repetition constructs
is how to deal with situations where the input data structure doesn't
match one-to-one with the desired configuration.
This adds some full worked examples of two common situations that have
come up in questions. To avoid adding a lot of extra content to the
already-large "expressions" and "resources" pages, the main bulk of this
new content lives with the relevant functions themselves as a full example
of one thing they are good for, and then we'll link to them from the two
general documentation sections where folks are likely to be reading when
they encounter the problem.
Based on some common questions and feedback since the v0.12.0 release,
here we add some small additional content to the documentation for
"dynamic" blocks, covering how to access the keys of the collection being
iterated over and how to fold multiple collections into a single one to
achieve the effect of a nested iteration.
The "terraform fmt" command produces a different canonical form than we
were showing in our examples here. Our examples should always reflect the
conventions applied by "terraform fmt" to avoid confusion.
(This particular decision is a pragmatic one because the formatter design
needs to use the same rules for the colon in the ? : conditional operator
as for the colon in "for" expressions.)
Since references to attributes of resources are by far the most common
reference type, and the mapping of resource type config to the attributes
is not always obvious, here we give some real examples of patterns for
accessing different configuration constructs within resource blocks along
with the resource type's exported attributes.
Since we don't have any real examples of labelled nested blocks yet (the
current SDK doesn't support them) I've included a hypothetical example for
now just to establish the patterns around them in preparation for
beginning to introduce them as we roll out this feature in the SDK.
This commit is a wide-ranging set of edits to the pages under
/docs/configuration. Among other things, it
- Separates style conventions out into their own page.
- Separates type constraints and conversion info into their own page.
- Conflates similar complex types a little more freely, since the distinction is
only relevant when restricting inputs for a reusable module or resource.
- Clarifies several concepts that confused me during edits.
This rewrite of the "Configuration Syntax" page now gives some more detail
on the top-level structural constructs and de-emphasizes the name "HCL"
as subordinate to "the Terraform language".
It also now includes some commentary on valid identifiers and comments,
and issues around character encodings and line endings.
In addition, we now have a new "Expressions" page that replaces the old
"Interpolation Syntax" page, covering the expression language features
we inherit from HCL and how they behave in the context of Terraform.
The "Expressions" page currently links to a page about the built-in
functions which does not yet exist. This will be created in a later
commit.
Martin Atkins