Convert ERB code into Ruby before type-checking by felixefelip · Pull Request #1836 · soutaro/steep

felixefelip · 2025-09-08T14:54:37Z

ERB to Ruby code conversion is needed to type-check ERB.

Input:

<html>
  <body>
    <ul>
    <% languages.each do |langage| %>
      <li><%= language %>
    <% end %>
    </ul>
  </body>
</html>

Output: (replace HTML tags with whitespace)

      
        
        
       languages.each do |langage|   
              language   
       end

refs: #1409

Use class << self for private methods

ParadoxV5 · 2025-09-08T17:18:07Z

Good idea, but I suggest making use of ERB::Compiler so you don’t have to parse things yourself.

Additionally, ERB isn’t limited to Rails, let alone HTML.
Your parser probably doesn’t care, but the test appears designed for Rails only.

Supercedes Steepfile: Allow to change the extension of the source files #1454
Do we want to move this to RBS?

felixefelip · 2025-09-09T00:25:40Z

@ParadoxV5 thanks for the review!

Good idea, but I suggest making use of ERB::Compiler so you don’t have to parse things yourself.

The ERB::Compiler looks great, I'm going to use it.

Additionally, ERB isn’t limited to Rails, let alone HTML. Your parser probably doesn’t care, but the test appears designed for Rails only.

My fault, I'm used ERB only with Rails, I'm going to adjust the tests examples.

Supercedes Steepfile: Allow to change the extension of the source files #1454

Do we want to move this to RBS?

Regarding moving this to RBS, I will analyze the projects better to give an opinion.

felixefelip · 2025-10-19T19:59:40Z

@ParadoxV5 I have not found a way to use ERB::Compiler for the proposal of this PR. Could you instruct me on how to use it, please?

Alternatively, I found the Herb that almost provides the parser we need. Herb just doesn't provide a public API with Ruby code with semicolons, but I'm trying to make a contribution to doing that here. It's ok to use that?

…ruby_before_type_checking

ParadoxV5 · 2025-10-25T22:48:53Z

@felixefelip:

Could you instruct me on how to use it, please?

The documentation above class ERB::Compiler reads: (formatting mine)

expand/collapse section

Internally ERB does something like this to generate the code returned by ERB#src:

compiler = ERB::Compiler.new('<>')
compiler.pre_cmd    = ["_erbout=+''"]
compiler.put_cmd    = "_erbout.<<"
compiler.insert_cmd = "_erbout.<<"
compiler.post_cmd   = ["_erbout"]

code, enc = compiler.compile("Got <%= obj %>!\n")
puts code

Generates:

  #coding:UTF-8
  _erbout=+''; _erbout.<< "Got ".freeze; _erbout.<<(( obj ).to_s); _erbout.<< "!\n".freeze; _erbout

By default the output is sent to the print method. For example:

compiler = ERB::Compiler.new('<>')
code, enc = compiler.compile("Got <%= obj %>!\n")
puts code

Generates:

#coding:UTF-8
print "Got ".freeze; print(( obj ).to_s); print "!\n".freeze

That means, ERB::Compiler.new(flags).compile(erb_file).first generates a string containing code that ERB executes to process ERB files, with Ruby instructions as-is and ERB text (e.g., HTML) outputted via Kernel#print.
You can pass this generated code to some Steep API (or dump to a temporary file if all fails).
You can also optionally configure an ERB::Compiler to be more Steep-user-friendly.
(There might be a way to completely ignore the verbatim texts, too.)

erb = ERB::Compiler.new nil
erb.put_cmd = erb.insert_cmd= "\n"
puts erb.compile('Got <%= process(obj) %>!').first

#coding:UTF-8

 "Got ".freeze;
(( process(obj) ).to_s);
 "!".freeze

It's ok to use that?

Assuming Herb.extract_ruby works with non-HTML as well, then my only concern is that ERB is still preferable for its popularity and StdLib status.

felixefelip · 2025-10-27T06:52:35Z

Thanks for the instructions @ParadoxV5!

I might have misunderstood some part, but I still couldn't to handle the verbatim texts like .freeze with the ERB::Compiler, and it's important the parsed code to preserve the exact number and position characters of original source code to display the Steep diagnostics. ERB::Compiler seems to be more designed to use for Kernel#print and not for a parser.

) This pull request adds `semicolons`, `comments`, and `preserve_positions` options to `Herb.extract_ruby` across all language bindings (Ruby, JavaScript, Java, Rust). This was originally requested to use the extract Ruby code with semicolons in Steep/RBS, more specifically in this PR: soutaro/steep#1836. It's because we need the Ruby code with semicolons to display the static typing errors correctly. I think this functionality could also be used in others projects like Sorbet and Packwerk. Resolves #100 --------- Co-authored-by: Felipe Felix <felipe.felix@maino.com.br> Co-authored-by: Everton <e.santos081992@gmail.com> Co-authored-by: Marco Roth <marco.roth@intergga.ch>

…ruby_before_type_checking

felixefelip · 2026-03-22T07:46:43Z

Hello @ParadoxV5,

Sorry for the long time to update this PR.

I managed the merge of the adjustment in Herb gem to make Herb compatible for this PR, as I mentioned here #1836 (comment)

So I already added it on this PR in this commit: 4841deb

It's okay to proceed in this way?

Convert ERB code into Ruby before type-checking

63cbedc

Use class << self for private methods

felixefelip force-pushed the support_erb/convert_erb_code_into_ruby_before_type_checking branch from fd6e3c4 to 63cbedc Compare September 8, 2025 15:34

felixefelip mentioned this pull request Oct 19, 2025

Extractor: Add extract_ruby_options across all language bindings marcoroth/herb#675

Merged

Merge branch 'soutaro:master' into support_erb/convert_erb_code_into_…

ba8c095

…ruby_before_type_checking

soutaro added this to the Steep 2.0 milestone Mar 13, 2026

Merge branch 'soutaro:master' into support_erb/convert_erb_code_into_…

7dec802

…ruby_before_type_checking

felixefelip force-pushed the support_erb/convert_erb_code_into_ruby_before_type_checking branch from 78925c9 to 4867dce Compare March 22, 2026 07:25

Use Herb gem to extract Ruby code from ERB

4841deb

felixefelip force-pushed the support_erb/convert_erb_code_into_ruby_before_type_checking branch from 4867dce to 4841deb Compare March 22, 2026 07:32

soutaro modified the milestones: Steep 2.0, Steep 2.1 Apr 14, 2026

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Convert ERB code into Ruby before type-checking#1836

Convert ERB code into Ruby before type-checking#1836
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felixefelip:support_erb/convert_erb_code_into_ruby_before_type_checking

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