Add support for Packer

[wzyboy]

This PR adds basic fixer support for Packer.

Terraform and Packer are both developed by HashiCorp and share the same HCL syntax. However, terraform fmt and packer fmt cannot be used inter-changably.

I have no experience with VimL, so I just copied the terraform fixer (and its test) into packer variant and it seems to work fine and all tests passed.

Please feel free to edit the PR if I made n00b mistakes on VimL.

[hsanson]

Looks good but needs to also update documentation:

1. Add an entry to doc/ale-hcl.txt for packer fixer.
2. Add an entry to supported-tools.md file.
3. Add an entry to ale-supported-languages-and-tools.txt
4. Add an entry to section 7.6 in ale.txt

Note that in doc/ale-hcl.txt the terraform-fmt entry is just a link to the doc/ale-terraform.txt entry. For Packer you do not want a link, instead you want to add the documentation itself.

Also ensure the entries on all these files are alphabetically ordered. packer-fmt comes before terraform-fmt on all the documents.

[hsanson]

Sorry, I believe my last comment should have been more details. My understanding is that Packer is a tool to format HCL andthat HCL is the file type. If this is the case then:

1. The doc/ale-packer.txt file in unnecessary. The contents you added in there should be directly inside the doc/ale-hcl.txt file. These doc/ale-xxx.txt files are per file type (e..g HCL) not per tool. Simply remove the doc/ale-packer.txt file and add the contents to the ale-hcl-packer-fmt section in doc/ale-hcl.txt
2. Update the index files by moving the packer entry belo the hcl entry and point them to ale-hcl-packer-fmt.

[wzyboy]

@hsanson Hi, the relation between HCL and Packer is as follows:

1. Terraform uses HCL with file extensions .tf, .tfvars, and .hcl;
2. Packer uses HCL with file extensions .pkr.hcl and .pkrvars.hcl;
3. The terraform fmt and packer fmt commands can only work on their own files.

IMHO Packer deserves its own format entry because only packer fmt can format Packer's HCL. You cannot format Packer's HCL with terraform fmt, and vice versa. On the other hand, Terraform and Packer both call their DSL "HCL" so it makes sense to mention the two tools in ale/doc-hcl.txt.

[hsanson]

I see, thanks for the explanation. If packer is its own file type then documentation is ok as it is and I would recommend to add "packer" in the suggested fixer registry and remove "hcl':

'suggested_filetypes': ['packer'],

This way the fixer wont trigger for all hcl files, only for packer files. I would also remove hcl from the suggested_filetypes for terraform. If not the terraform firxer can be triggered for packer files with hcl extension.

Also please add this to you ale_linters configuration so Vim warns you about linter issues that are failing now:

let g:ale_linters = {
  \   'vim': ['vint', 'ale_custom_linting_rules'],
\ }

[wzyboy]

I agree with you that packer ft should be in the suggested_filetypes of packer tool. However, I believe suggesting both packer and terraform tools for hcl filetype makes sense, because:

1. As I mentioned above, the two tools share the HCL syntax, for some files (e.g. variables ), the formats are identical. It would be hard (if not impossible) to tell them apart. It's just like for ft=yaml, ALE also suggests circleci.
2. Exsting tools already associate *.hcl files with ft=hcl. So I won't remove hcl from the suggested file types of terraform tool.

As of the linting errors, I cannot determine which part is wrong. I already have vint in my $PATH and also tried :ALEFix align_help_tags before submitting the PR. Could you help me determine why CI is failing?

[hsanson]

You need to add packer-fmt under the HCL section on all index files to make the linter happy:

diff --git a/doc/ale-supported-languages-and-tools.txt b/doc/ale-supported-languages-and-tools.txt
index 6852e80a..047020bf 100644
--- a/doc/ale-supported-languages-and-tools.txt
+++ b/doc/ale-supported-languages-and-tools.txt
@@ -239,6 +239,7 @@ Notes:
   * `stack-ghc`
   * `stylish-haskell`
 * HCL
+  * `packer-fmt`
   * `terraform-fmt`
 * HTML
   * `VSCode HTML language server`
diff --git a/doc/ale.txt b/doc/ale.txt
index 8e73ac2b..db646377 100644
--- a/doc/ale.txt
+++ b/doc/ale.txt
@@ -2909,6 +2909,7 @@ documented in additional help files.
     hie...................................|ale-haskell-hie|
     ormolu................................|ale-haskell-ormolu|
   hcl.....................................|ale-hcl-options|
+    packer-fmt............................|ale-hcl-packer-fmt|
     terraform-fmt.........................|ale-hcl-terraform-fmt|
   help....................................|ale-help-options|
     cspell................................|ale-help-cspell|
diff --git a/supported-tools.md b/supported-tools.md
index cc30fc61..f3f3a117 100644
--- a/supported-tools.md
+++ b/supported-tools.md
@@ -248,6 +248,7 @@ formatting.
   * [stack-ghc](https://haskellstack.org/)
   * [stylish-haskell](https://github.com/jaspervdj/stylish-haskell)
 * HCL
+  * [packer-fmt](https://github.com/hashicorp/packer)
   * [terraform-fmt](https://github.com/hashicorp/terraform)
 * HTML
   * [VSCode HTML language server](https://github.com/hrsh7th/vscode-langservers-extracted)

[hsanson]

Great, thanks for all the changes. Looking good.