terraform-provider: add image datasource (#2642)

* terraform-provider: init

Signed-off-by: Moritz Sanft <58110325+msanft@users.noreply.github.com>

* terraform-provider: add basic docgen

Signed-off-by: Moritz Sanft <58110325+msanft@users.noreply.github.com>

* terraform-provider: fix build steps

Signed-off-by: Moritz Sanft <58110325+msanft@users.noreply.github.com>

* terraform-provider: extend build process and docgen

Signed-off-by: Moritz Sanft <58110325+msanft@users.noreply.github.com>

* dev-docs: document provider usage

Signed-off-by: Moritz Sanft <58110325+msanft@users.noreply.github.com>

* bazel: upload aspect lib mirror

Signed-off-by: Moritz Sanft <58110325+msanft@users.noreply.github.com>

* terraform-provider: don't try to create lockfiles

Signed-off-by: Moritz Sanft <58110325+msanft@users.noreply.github.com>

* bazel: fix shellcheck issues

* bazel: separate paths to check

* terraform-provider: clean up old files

* terraform-provider: update provider resource

* terraform-provider: add image data source

* dev-docs: remove unnecessary init

* bazel: adhere to Terraform naming expectations

* terraform-provider: fix expected data type

* terraform-provider: generate docs

* terraform-provider: improve errors

* terraform-provider: add acceptance tests for data source

* terraform-provider: fix dependencies

* bazel: quote var reference

* terraform-provider: make region optional

* terraform-provider: bind imagefetcher to data source

* bazel: tidy

* terraform-provider: remove unused parameter

* terraform-provider: remove unused parameter

* terraform-provider: extend acceptance tests

* terraform-provider: allow tests to be ran without Bazel

* dev-docs: document testing

* terraform-provider: set binary path accordingly

* dev-docs: document docgen process for the provider

* bazel: run acceptance test in writable environment

* bazel: try to write to `$TMPDIR`

* terraform-provider: style nits

* terraform-provider: leave TODO

* bazel: tidy

* terraform-provider: regenerate docs

* terraform-provider: fix comment

---------

Signed-off-by: Moritz Sanft <58110325+msanft@users.noreply.github.com>

terraform-provider-constellation/internal/provider/provider_test.go

@@ -7,22 +7,66 @@ SPDX-License-Identifier: AGPL-3.0-only
 package provider
 
 import (
+	"fmt"
+	"os"
 	"testing"
 
+	"github.com/bazelbuild/rules_go/go/runfiles"
 	"github.com/hashicorp/terraform-plugin-framework/providerserver"
 	"github.com/hashicorp/terraform-plugin-go/tfprotov6"
 )
 
+const (
+	// testingConfig is a shared configuration to combine with the actual
+	// test configuration so the constellation provider is properly configured
+	// for acceptance testing.
+	testingConfig = `provider "constellation" {}`
+)
+
 // testAccProtoV6ProviderFactories are used to instantiate a provider during
 // acceptance testing. The factory function will be invoked for every Terraform
 // CLI command executed to create a provider server to which the CLI can
 // reattach.
 var testAccProtoV6ProviderFactories = map[string]func() (tfprotov6.ProviderServer, error){
-	"scaffolding": providerserver.NewProtocol6WithError(New("test")()),
+	"constellation": providerserver.NewProtocol6WithError(New("test")()),
 }
 
-func testAccPreCheck(_ *testing.T) {
-	// You can add code here to run prior to any test case execution, for example assertions
-	// about the appropriate environment variables being set are common to see in a pre-check
-	// function.
+// bazelSetTerraformBinaryPath sets the path to the Terraform binary for
+// acceptance testing when running under Bazel.
+func bazelSetTerraformBinaryPath(t *testing.T) {
+	if v := os.Getenv("TF_ACC"); v != "1" {
+		t.Fatal("TF_ACC must be set to \"1\" for acceptance tests")
+	}
+
+	// If we don't run under Bazel, we need to use the host Terraform binary.
+	// Print a warning and return without setting the path.
+	if !runsUnderBazel() {
+		fmt.Println(
+			"Test is not runding under Bazel.\n" +
+				"Using Host Terraform binary for acceptance testing.\n" +
+				"Tests results may vary from the defaults (which run under Bazel).",
+		)
+		return
+	}
+
+	tfPath := os.Getenv("TF_ACC_TERRAFORM_PATH")
+	if tfPath == "" {
+		t.Fatal("TF_ACC_TERRAFORM_PATH must be set for acceptance tests")
+	}
+
+	absTfPath, err := runfiles.Rlocation(tfPath)
+	if err != nil {
+		panic("could not find path to artifact")
+	}
+
+	// Set the path to the absolute Terraform binary for acceptance testing.
+	t.Setenv("TF_ACC_TERRAFORM_PATH", absTfPath)
 }
+
+// runsUnderBazel checks whether the test is ran under bazel.
+func runsUnderBazel() bool {
+	return runsUnder == "bazel"
+}
+
+// runsUnder is redefined only by the Bazel build at link time.
+var runsUnder = "go"