Merge pull request #7503 from hashicorp/better_empty_checksum_error_step_download

step_download: display clearer error messages, also when the checksum is not set

common/step_download.go

@@ -82,7 +82,9 @@ func (s *StepDownload) Run(ctx context.Context, state multistep.StateBag) multis
 		errs = append(errs, err)
 	}
 
-	state.Put("error", fmt.Errorf("Downloading file: %v", errs))
+	err := fmt.Errorf("error downloading %s: %v", s.Description, errs)
+	state.Put("error", err)
+	ui.Error(err.Error())
 	return multistep.ActionHalt
 }
 
@@ -104,7 +106,7 @@ func (s *StepDownload) download(ctx context.Context, ui packer.Ui, source string
 		q.Set("checksum", s.Checksum)
 		u.RawQuery = q.Encode()
 	} else if s.ChecksumType != "none" {
-		return "", fmt.Errorf("Empty checksum")
+		return "", fmt.Errorf("empty checksum, a checksum or a 'none' checksum type must be set")
 	}
 
 	targetPath := s.TargetPath

website/source/docs/builders/virtualbox-ovf.html.md.erb

@@ -67,6 +67,13 @@ builder.
 -   `source_path` (string) - The path to an OVF or OVA file that acts as the
     source of this build. It can also be a URL.
 
+-   `checksum` (string) - The checksum for the `source_path` file. The 
+    algorithm to use when computing the checksum can be optionally specified 
+    with `checksum_type`. When `checksum_type` is not set packer will guess the 
+    checksumming type based on `checksum` length. `checksum` can be also be a 
+    file or an URL, in which case `checksum_type` must be set to `file`; the 
+    go-getter will download it and use the first hash found.
+
 ### Optional:
 
 -   `boot_command` (array of strings) - This is an array of commands to type
@@ -82,9 +89,6 @@ builder.
     five seconds and one minute 30 seconds, respectively. If this isn't
     specified, the default is `10s` or 10 seconds.
 
--   `checksum` (string) - The checksum for the OVA file. The type of the
-    checksum is specified with `checksum_type`, documented below.
-
 -   `checksum_type` (string) - The type of the checksum specified in `checksum`.
     Valid values are `none`, `md5`, `sha1`, `sha256`, or `sha512`. Although the
     checksum will not be verified when `checksum_type` is set to "none", this is