Previously we were just loading the module and asserting no diagnostics,
but that is not really good enough since if we install modules incorrectly
it's possible that we are still able to load an empty configuration
successfully.
Now we'll do some basic inspecetion of the module tree that results from
loading what we installed, to ensure that all of the expected modules
are present at the right locations in the tree.
This will provide the functionality of "terraform init -from-module=...",
which uses the contents of a given module to populate the working
directory.
This mechanism is intended for installing e.g. examples from Terraform
Registry or elsewhere. It's not fully-general since it can't reasonably
install a module from a subdir that refers up to a parent directory, but
that isn't an issue for all reasonable uses of this option.
Originally the hope was to use the afero filesystem abstraction for all
loader operations, but since we install modules using go-getter we cannot
(without a lot of refactoring) support vfs for installation.
The vfs use-case is for reading configuration from plan zip files anyway,
and so we have no real reason to support installation into a vfs. For now
at least we will just add the possibility that a loader might not be
install-capable. At the moment we have no non-install-capable loaders, but
we'll add one later once we get to loading configuration from plan files.
Unlike the old installer in config/module, this uses new-style
installation directories that include the static module path so that paths
we show in diagnostics will be more meaningful to the user.
As before, we retrieve the entire "package" associated with the given
source string, rather than any given subdirectory directly, because the
retrieved module may contain ../ references into parent directories which
must be resolvable after extraction.
Enough of the InstallModules method to install local modules (those with
relative paths). "Install" is actually a bit of an exaggeration for these
since we actually just record them in our manifest after verifying that
the source directory exists.
This is a change of behavior relative to the old module installer since
we no longer create a symlink to the module directory inside the
.terraform/modules directory. Instead, we record the module's true
location in our manifest so that the loader will find it later.
The use of a symlink here predated the manifest file. Now that we have a
manifest file the symlinks are redundant. Using the "natural" location of
the module leads to more helpful error messages, since we'll refer to
the module path as the user expects it, rather than to an internal alias.
Previously the behavior for loading and installing modules was included in
the same package as the representation of the module tree (in the
config/module package).
In our new world, the model of a module tree (now called a "Config") is
included in "configs" along with the Module and File structs. This new
package replaces the loading and installation functionality previously
in config/module with new equivalents that work with the model objects
in "configs".
As of this commit, only the loading functionality is implemented. The
installation functionality will follow in subsequent commits.
Martin Atkins