# Evaluation How pravo turns the CUE files of a directory into one value, finds resources by identity and builds the dependency graph before any provider is asked anything. Time: 11 minutes Evaluation is the first half of every run. It reads files and nothing else. Its results are one value, the resources found in it, and a graph of the dependencies between them. `pravo validate` and `pravo eval` stop when evaluation is done. `pravo plan` and `pravo apply` continue with the providers. ## One package, one value The directory in which you run pravo is the root. pravo loads the CUE package in it. Every file of the package joins it, in any order, and CUE unifies the files into one value. A file in a subdirectory joins the package only when something imports it. Work in an empty directory. The first two files hold data and no provider, so `pravo eval` runs without one. `pravo init` creates the CUE module that the package needs. ```cue file=base.cue package estate env: *"dev" | "prod" @tag(env) tags: owner: "platform" ``` ```cue file=extra.cue package estate tags: stage: env ``` ```sh run pravo init ``` ```text out Providers: Created cue.mod/module.cue pravo has been initialised. Run "pravo plan" to see what it would do. ``` ```sh run pravo eval ``` ```text out env: "dev" tags: { owner: "platform" stage: "dev" } ``` `stage` in the second file refers to `env` in the first. The result does not depend on the order of the files or of the lines. A field with an `@tag()` attribute takes its value from the command line. ```sh run pravo eval -t env=prod ``` ```text out env: "prod" tags: { owner: "platform" stage: "prod" } ``` A tag is part of the specification. A saved plan records the tags that it was made with. `-T` injects the system variables of CUE, such as `os` and `arch`. The files of a package carry one package name. A file with another name, or with none, is an error that names the file. ```cue file=other.cue status=rejected package other size: 1 ``` ```sh run exit=6 pravo validate ``` ```text out Error: loading .: other.cue is package other; the other files are package estate ``` ```sh run rm other.cue ``` ## Provider definitions are part of the value A provider contributes definitions to the value. `pravo init` reads the schema of each provider and writes a CUE package from it under `cue.mod/gen`. A resource is a struct that unifies with one definition from that package. The definition lists every attribute of the type with its type. It is closed, so an attribute that the schema does not list is a conflict. Add a provider file and run `pravo init` again. ```cue file=providers.cue package estate import ( "pravo.dev/pravo" rnd "pravo.dev/providers/hashicorp/random" loc "pravo.dev/providers/hashicorp/local" ) $settings: pravo.#Settings & {refresh: "1h"} $random: rnd.#Provider $local: loc.#Provider ``` ```sh run pravo init ``` ```text out Configuration does not load yet; generating schemas for the declared providers first. Providers: ... pravo has been initialised. Run "pravo plan" to see what it would do. ``` A misspelt attribute fails at evaluation. The error names the path and the line. ```cue file=typo.cue status=rejected package estate oops: $random.#Resource.random_pet & {lenght: 2} ``` ```sh run exit=6 pravo validate ``` ```text out Error: evaluating .: oops.lenght: field not allowed: ./typo.cue:3:39 ``` No provider process has started. The check needs the generated package and nothing else. The next block adds three resources, removes the typo and validates again with `-v`. The filter keeps the line that discovery prints and any line that reports a provider process. ```sh run rm typo.cue ``` ```cue file=resources.cue package estate port: $random.#Resource.random_integer & { min: 20000 max: 29999 seed: "web" } // A plain field. It is not a resource, but web depends on port through it. listen: port.result web: $local.#Resource.local_file & { filename: "web-\(env).conf" content: "port = \(listen)\n" } // A field that holds a whole resource is a second resource. copy: port // A definition and a hidden field are not searched. #Pet: $random.#Resource.random_pet _draft: $random.#Resource.random_pet & {length: 9} ``` ```sh run pravo -v validate 2>&1 \ | sed -E 's/^\+[0-9.]+s debug //; s/ (dir|path|location)=[^ ]+//g' \ | grep -E '^(loaded|provider started|Success)' ``` ```text out loaded managed=3 data=0 ephemeral=0 calls=0 outputs=0 providers=2 moves=0 imports=0 took=