HCL2: version block: test validation & document version/availability (#10298)

* HCL2: Test that the packer block passes in packer validate

* HCL2: Test invalid packer blocks are invalid

* docs: state from which version the packer block is available

command/test-fixtures/validate/build.pkr.hcl

@@ -1,3 +1,7 @@
+packer {
+  required_version = ">= v1.0.0"
+}
+
 source "file" "chocolate" {
   target = "chocolate.txt"
   content = "chocolate"

command/test-fixtures/validate/invalid_packer_block.pkr.hcl

@@ -0,0 +1,3 @@
+packer {
+  version = ">= v1.0.0"
+}

command/validate_test.go

@@ -26,6 +26,9 @@ func TestValidateCommand(t *testing.T) {
 
 		// wrong version field
 		{path: filepath.Join(testFixture("version_req", "wrong_field_name")), exitCode: 1},
+
+		// wrong packer block
+		{path: filepath.Join(testFixture("validate", "invalid_packer_block.pkr.hcl")), exitCode: 1},
 	}
 
 	for _, tc := range tt {

website/pages/docs/from-1.5/blocks/packer.mdx

@@ -11,6 +11,8 @@ description: |-
 
 `@include 'from-1.5/beta-hcl2-note.mdx'`
 
+-> **Note:** The Packer block is only available in Packer v1.6.5 and later.
+
 The `packer` configuration block type is used to configure some
 behaviors of Packer itself, such as the minimum required Packer version needed to 
 apply your configuration.