Consider local_directory Data Source

[bflad]

Terraform CLI and Provider Versions

N/A

Use Cases or Problem Statement

The Terraform configuration language has the fileexists() function which returns successfully if a file exists at a given path, however it does not currently handle directories. Even if it was adjusted to support directories (or created as a separate function), as with most configuration language functions, the result is evaluated before the rest of the graph. This can cause issues for practitioners wishing to check/manage directories generated/updated during the graph for purposes of clearer error messaging or other operations which might need a listing of all files within a directory.

While today we generally rely on the function documentation to warn practitioners about this potential issue, it may make sense to provide a graph-aware solution for the use case.

Proposal

Create a new local_directory data source which attempts to read a local filesystem directory. It should error if the directory does not exist otherwise return a set of file paths, for potential usage elsewhere in a Terraform configuration.

As a design sketch of potential usage:

# Ensure example directory exists, potentially due to
# another graph node with side effects creating the directory
# or as a precondition for other graph nodes
data "local_directory" "example" {
  path = "${path.module}/example"
}

# Another way to check directory exists and has files, using new check block functionality to only raise warning
check {
  data "local_directory" "node_modules" {
    path = "${path.module}/node_modules"
  }

  assert {
    condition = length(data.local_directory.node_modules.file_paths) > 0
    error_message = "${data.local_directory.node_modules.path} does not contain any files"
  }
}

Proposed data source configurable attributes:

• path - String, required, the path to the directory

Proposed data source computed attributes:

• file_paths - Set of strings, the paths to all files within directory

How much impact is this issue causing?

Medium

Additional Information

• fileexists() function proposal to handle directories (or preferably create direxists() function): fileexists should not return an error when subject is a directory (should always return boolean) terraform#25316
• local_directories data source proposal: Consider local_directories Data Source #215

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