Engine: Compile-time optimizations for Action View tag helpers (#1613)

This pull request adds compile-time optimization support for Action View
tag helpers to `Herb::Engine`.

When `optimize: true` is passed to `Herb::Engine`, the parser transforms
Action View helper calls (`tag.*`, `content_tag`, `link_to`,
`image_tag`, `javascript_tag`, `javascript_include_tag`,
`turbo_frame_tag`) into their HTML equivalents at compile time,
producing optimized Ruby output that avoids runtime helper dispatch.

When compile-time optimizations are enabled, the engine checks whether
the template contains supported Action View helpers via the
`Herb::ActionView::HelperRegistry.supported` method. If helpers are
detected, the parser is invoked with `action_view_helpers: true` and
`transform_conditionals: true`, which also handles postfix if/unless and
ternary conditionals containing helper calls.

The pull request also includes comprehensive snapshot-based tests for
all supported helpers, an `assert_optimized_output_match` helper that
validates optimized output against both standard Herb and
ActionView+Erubi to ensure the rendered output matches.

Additionally, we added a YAML-driven benchmark framework in
`bench/action_view/` with a `bin/bench` CLI for compile-time and
render-time comparisons. Early benchmarks show render-time improvements
of 3-22x depending on the template, with a realistic 192-line page
layout rendering 22x faster, and a helper-heavy template with all static
values reaching up to 150x faster.

The trade-off is compile time: Herb's parser is currently 10-90x slower
than Erubi at compile time, so optimization adds overhead that needs to
be amortized over multiple renders. But this is typically won back with
15-100 renders depending on template complexity and could also be done
ahead of time, instead of the current on-the-fly approach used in Action
View today.

  > [!WARNING]
> Compile-time optimizations are experimental. Output may differ from
standard ActionView rendering.

<img alt="CleanShot 2026-04-05 at 23 58 07@2x"
src="https://github.com/user-attachments/assets/da407b38-e101-47e9-96a7-b58ed36fdf9d"
/>

Resolves #653
Enables #1111

Author: marcoroth

.rubocop.yml

@@ -62,6 +62,7 @@ Metrics/CyclomaticComplexity:
     - lib/herb/prism_inspect.rb
     - lib/herb/engine/**/*.rb
     - templates/template.rb
+    - bench/**/*
 
 Metrics/MethodLength:
   Max: 20
@@ -76,6 +77,7 @@ Metrics/MethodLength:
     - test/fork_helper.rb
     - test/snapshot_utils.rb
     - bin/**/*
+    - bench/**/*
 
 Metrics/AbcSize:
   Exclude:
@@ -93,6 +95,8 @@ Metrics/AbcSize:
     - test/snapshot_utils.rb
     - test/engine/rails_compatibility_test.rb
     - bin/**/*
+    - bench/**/*
+    - test/engine/action_view/action_view_test_helper.rb
 
 Metrics/ClassLength:
   Exclude:
@@ -112,6 +116,7 @@ Metrics/ModuleLength:
     - test/**/*.rb
     - templates/**/*.rb
     - bin/lib/compare_helpers.rb
+    - bench/**/*
 
 Metrics/BlockLength:
   Max: 30
@@ -145,6 +150,7 @@ Metrics/PerceivedComplexity:
     - templates/template.rb
     - test/**/*.rb
     - bin/**/*
+    - bench/**/*
 
 Layout/LineLength:
   Enabled: false
@@ -177,6 +183,7 @@ Security/Eval:
     - bin/erubi-render
     - bin/compare-render
     - bin/compare-render
+    - bench/action_view/benchmark_helper.rb
 
 Security/MarshalLoad:
   Exclude:
@@ -192,3 +199,6 @@ Lint/UnusedMethodArgument:
 
 Style/IfUnlessModifier:
   Enabled: false
+
+Style/DocumentDynamicEvalDefinition:
+  Enabled: false

Gemfile

@@ -7,6 +7,8 @@ gemspec
 gem "prism", github: "ruby/prism", tag: "v1.9.0"
 
 gem "actionview", "~> 8.0"
+gem "benchmark"
+gem "charm"
 gem "digest", "~> 3.2"
 gem "erubi"
 gem "irb", "~> 1.16"
@@ -17,9 +19,11 @@ gem "rake", "~> 13.2"
 gem "rake-compiler", "~> 1.3"
 gem "rake-compiler-dock", "~> 1.11"
 gem "rbs-inline", "~> 0.12"
+gem "reactionview", "~> 0.3.0"
 gem "reline", "~> 0.6"
 gem "rubocop", "~> 1.71"
 gem "sorbet"
+gem "turbo-rails", "~> 2.0"
 
 # TODO: Remove once https://github.com/ruby/rbs/pull/2850 is merged and released
 gem "rbs", github: "marcoroth/rbs", branch: "psych-load-unsafe-file"

Gemfile.lock

@@ -46,6 +46,16 @@ PATH
 GEM
   remote: https://rubygems.org/
   specs:
+    actionpack (8.1.2)
+      actionview (= 8.1.2)
+      activesupport (= 8.1.2)
+      nokogiri (>= 1.8.5)
+      rack (>= 2.2.4)
+      rack-session (>= 1.0.1)
+      rack-test (>= 0.6.3)
+      rails-dom-testing (~> 2.2)
+      rails-html-sanitizer (~> 1.6)
+      useragent (~> 0.16)
     actionview (8.1.2)
       activesupport (= 8.1.2)
       builder (~> 3.1)
@@ -67,8 +77,40 @@ GEM
       uri (>= 0.13.1)
     ast (2.4.3)
     base64 (0.3.0)
+    benchmark (0.5.0)
     bigdecimal (4.0.1)
+    bubbles (0.1.1)
+      bubbletea
+      harmonica
+      lipgloss
+    bubbletea (0.1.4-aarch64-linux-gnu)
+      lipgloss (~> 0.1)
+    bubbletea (0.1.4-aarch64-linux-musl)
+      lipgloss (~> 0.1)
+    bubbletea (0.1.4-arm64-darwin)
+      lipgloss (~> 0.1)
+    bubbletea (0.1.4-x86_64-darwin)
+      lipgloss (~> 0.1)
+    bubbletea (0.1.4-x86_64-linux-gnu)
+      lipgloss (~> 0.1)
+    bubbletea (0.1.4-x86_64-linux-musl)
+      lipgloss (~> 0.1)
+    bubblezone (0.1.2-aarch64-linux-gnu)
+    bubblezone (0.1.2-aarch64-linux-musl)
+    bubblezone (0.1.2-arm64-darwin)
+    bubblezone (0.1.2-x86_64-darwin)
+    bubblezone (0.1.2-x86_64-linux-gnu)
+    bubblezone (0.1.2-x86_64-linux-musl)
     builder (3.3.0)
+    charm (0.1.0)
+      bubbles
+      bubbletea
+      bubblezone
+      glamour
+      gum
+      harmonica
+      lipgloss
+      ntcharts
     concurrent-ruby (1.3.6)
     connection_pool (3.0.2)
     crass (1.0.6)
@@ -95,22 +137,39 @@ GEM
     ffi (1.17.3-x86_64-linux-gnu)
     ffi (1.17.3-x86_64-linux-musl)
     fileutils (1.8.0)
+    glamour (0.2.2-aarch64-linux-gnu)
+    glamour (0.2.2-aarch64-linux-musl)
+    glamour (0.2.2-arm64-darwin)
+    glamour (0.2.2-x86_64-darwin)
+    glamour (0.2.2-x86_64-linux-gnu)
+    glamour (0.2.2-x86_64-linux-musl)
+    gum (0.3.2-aarch64-linux)
+    gum (0.3.2-arm64-darwin)
+    gum (0.3.2-x86_64-darwin)
+    gum (0.3.2-x86_64-linux)
+    harmonica (0.1.1)
     i18n (1.14.8)
       concurrent-ruby (~> 1.0)
     io-console (0.8.2)
     irb (1.16.0)
       pp (>= 0.6.0)
       rdoc (>= 4.0.0)
       reline (>= 0.4.2)
-    json (2.18.0)
+    json (2.19.2)
     language_server-protocol (3.17.0.5)
     lint_roller (1.1.0)
+    lipgloss (0.2.2-aarch64-linux-gnu)
+    lipgloss (0.2.2-aarch64-linux-musl)
+    lipgloss (0.2.2-arm64-darwin)
+    lipgloss (0.2.2-x86_64-darwin)
+    lipgloss (0.2.2-x86_64-linux-gnu)
+    lipgloss (0.2.2-x86_64-linux-musl)
     listen (3.10.0)
       logger
       rb-fsevent (~> 0.10, >= 0.10.3)
       rb-inotify (~> 0.9, >= 0.9.10)
     logger (1.7.0)
-    loofah (2.25.0)
+    loofah (2.25.1)
       crass (~> 1.0.2)
       nokogiri (>= 1.12.0)
     lz_string (0.3.0)
@@ -120,18 +179,24 @@ GEM
     minitest-difftastic (0.2.1)
       difftastic (~> 0.6)
     mutex_m (0.3.0)
-    nokogiri (1.19.0-aarch64-linux-gnu)
+    nokogiri (1.19.2-aarch64-linux-gnu)
       racc (~> 1.4)
-    nokogiri (1.19.0-aarch64-linux-musl)
+    nokogiri (1.19.2-aarch64-linux-musl)
       racc (~> 1.4)
-    nokogiri (1.19.0-arm64-darwin)
+    nokogiri (1.19.2-arm64-darwin)
       racc (~> 1.4)
-    nokogiri (1.19.0-x86_64-darwin)
+    nokogiri (1.19.2-x86_64-darwin)
       racc (~> 1.4)
-    nokogiri (1.19.0-x86_64-linux-gnu)
+    nokogiri (1.19.2-x86_64-linux-gnu)
       racc (~> 1.4)
-    nokogiri (1.19.0-x86_64-linux-musl)
+    nokogiri (1.19.2-x86_64-linux-musl)
       racc (~> 1.4)
+    ntcharts (0.1.2-aarch64-linux-gnu)
+    ntcharts (0.1.2-aarch64-linux-musl)
+    ntcharts (0.1.2-arm64-darwin)
+    ntcharts (0.1.2-x86_64-darwin)
+    ntcharts (0.1.2-x86_64-linux-gnu)
+    ntcharts (0.1.2-x86_64-linux-musl)
     parallel (1.27.0)
     parser (3.3.10.1)
       ast (~> 2.4.1)
@@ -145,13 +210,30 @@ GEM
       date
       stringio
     racc (1.8.1)
+    rack (3.2.5)
+    rack-session (2.1.1)
+      base64 (>= 0.1.0)
+      rack (>= 3.0.0)
+    rack-test (2.2.0)
+      rack (>= 1.3)
+    rackup (2.3.1)
+      rack (>= 3)
     rails-dom-testing (2.3.0)
       activesupport (>= 5.0.0)
       minitest
       nokogiri (>= 1.6)
-    rails-html-sanitizer (1.6.2)
-      loofah (~> 2.21)
+    rails-html-sanitizer (1.7.0)
+      loofah (~> 2.25)
       nokogiri (>= 1.15.7, != 1.16.7, != 1.16.6, != 1.16.5, != 1.16.4, != 1.16.3, != 1.16.2, != 1.16.1, != 1.16.0.rc1, != 1.16.0)
+    railties (8.1.2)
+      actionpack (= 8.1.2)
+      activesupport (= 8.1.2)
+      irb (~> 1.13)
+      rackup (>= 1.0.0)
+      rake (>= 12.2)
+      thor (~> 1.0, >= 1.2.2)
+      tsort (>= 0.2)
+      zeitwerk (~> 2.6)
     rainbow (3.1.1)
     rake (13.3.1)
     rake-compiler (1.3.1)
@@ -167,6 +249,9 @@ GEM
       erb
       psych (>= 4.0.0)
       tsort
+    reactionview (0.3.0)
+      actionview (>= 7.0)
+      herb (>= 0.9.0, < 1.0.0)
     regexp_parser (2.11.3)
     reline (0.6.3)
       io-console (~> 0.5)
@@ -195,13 +280,19 @@ GEM
     strscan (3.1.7)
     terminal-table (4.0.0)
       unicode-display_width (>= 1.1.1, < 4)
+    thor (1.5.0)
     tsort (0.2.0)
+    turbo-rails (2.0.23)
+      actionpack (>= 7.1.0)
+      railties (>= 7.1.0)
     tzinfo (2.0.6)
       concurrent-ruby (~> 1.0)
     unicode-display_width (3.2.0)
       unicode-emoji (~> 4.1)
     unicode-emoji (4.2.0)
     uri (1.1.1)
+    useragent (0.16.11)
+    zeitwerk (2.7.5)
 
 PLATFORMS
   aarch64-linux
@@ -216,6 +307,8 @@ PLATFORMS
 
 DEPENDENCIES
   actionview (~> 8.0)
+  benchmark
+  charm
   digest (~> 3.2)
   erubi
   herb!
@@ -229,10 +322,12 @@ DEPENDENCIES
   rake-compiler-dock (~> 1.11)
   rbs!
   rbs-inline (~> 0.12)
+  reactionview (~> 0.3.0)
   reline (~> 0.6)
   rubocop (~> 1.71)
   sorbet
   steep!
+  turbo-rails (~> 2.0)
 
 BUNDLED WITH
    2.7.2