fix(sinatra): render ERB views in erubi mode (newline fidelity)

go.mod

@@ -41,7 +41,7 @@ require (
 	github.com/go-ruby-dry-struct/dry-struct v0.0.0-20260702152517-9e25a927a351
 	github.com/go-ruby-dry-types/dry-types v0.0.0-20260702150052-94ab5100a720
 	github.com/go-ruby-dry-validation/dry-validation v0.0.0-20260702151810-a274955bddac
-	github.com/go-ruby-erb/erb v0.0.0-20260629074717-0999ae4dd529
+	github.com/go-ruby-erb/erb v0.0.0-20260706152133-22f94a380d76
 	github.com/go-ruby-erubi/erubi v0.0.0-20260706150033-cfeeadde9120
 	github.com/go-ruby-etcd/etcd v0.0.0-20260704112801-4417ab26c89a
 	github.com/go-ruby-excon/excon v0.0.0-20260706115718-5ca851d0373f

go.sum

@@ -240,8 +240,8 @@ github.com/go-ruby-dry-types/dry-types v0.0.0-20260702150052-94ab5100a720 h1:Lc4
 github.com/go-ruby-dry-types/dry-types v0.0.0-20260702150052-94ab5100a720/go.mod h1:S+2r7EA5zp4E8JyaJ88koD8gT7k/JD9i8NGj6V6jIRM=
 github.com/go-ruby-dry-validation/dry-validation v0.0.0-20260702151810-a274955bddac h1:ry6nkQY0B7TQfJD34iTIEqVPgThNkcXFreD116X/o74=
 github.com/go-ruby-dry-validation/dry-validation v0.0.0-20260702151810-a274955bddac/go.mod h1:LHalD7pLKBYjablQtp55tlPahU5LHCXf0v0mSzmS6zE=
-github.com/go-ruby-erb/erb v0.0.0-20260629074717-0999ae4dd529 h1:md/l6ifEY6S0Iy1nBk5hVt5BhnWJRqhB08gVEsVvS28=
-github.com/go-ruby-erb/erb v0.0.0-20260629074717-0999ae4dd529/go.mod h1:HEJVI7jQ/BnjiSiu2Wj934QboEAgdv47RNOqvZb+nRw=
+github.com/go-ruby-erb/erb v0.0.0-20260706152133-22f94a380d76 h1:CenGI7B67vUppMG1+YV78+IgbmKArmokJFStknRlBxU=
+github.com/go-ruby-erb/erb v0.0.0-20260706152133-22f94a380d76/go.mod h1:HEJVI7jQ/BnjiSiu2Wj934QboEAgdv47RNOqvZb+nRw=
 github.com/go-ruby-erubi/erubi v0.0.0-20260706150033-cfeeadde9120 h1:+CId0Dae0fU9zVcyryFoY8l/cqTpFSEvgv9RBXiZDDU=
 github.com/go-ruby-erubi/erubi v0.0.0-20260706150033-cfeeadde9120/go.mod h1:jZJcpxqgDFkKAW7K6Z/WwrWdF7BQ78dYUopimi986ls=
 github.com/go-ruby-etcd/etcd v0.0.0-20260704112801-4417ab26c89a h1:aFqb/Uizc/H0UPz6uv5qWpyFVopuPlPjgXevBlV7HMo=

internal/vm/sinatra_erb.go

@@ -19,11 +19,18 @@ import (
 // _erbout buffer and returning the rendered String. That String becomes the Rack
 // response body via sinatraResult, exactly as under MRI Sinatra + Tilt.
 //
-// Trim mode and the output-buffer name match Tilt::ERBTemplate's defaults, which
-// Sinatra uses unchanged: trim "<>" (a code-only line's surrounding newlines are
-// removed) and eoutvar "_erbout". <%= %> interpolates unescaped (Sinatra does not
-// auto-escape unless :erb => { escape_html: true } is configured — a scoped
-// follow-up), <% %> is control flow.
+// The dialect and the output-buffer name match what Sinatra 4.x actually renders
+// with: since Sinatra 2.0 Tilt maps :erb to Tilt::ErubiTemplate, so views compile
+// through the erubi gem's Erubi::Engine, not classic MRI ERB. go-ruby-erb's
+// ModeErubi reproduces Erubi::Engine byte-for-byte (default engine options: trim
+// on, escape off), which is why the Sinatra render selects erb.ModeErubi here
+// (erubi has no trim_mode, so TrimMode is not passed) while the standalone
+// `require "erb"` / classic-ERB binding in erb.go stays in the default ModeERB.
+// The output buffer is eoutvar "_erbout" (Tilt's default). <%= %> interpolates
+// unescaped (Sinatra does not auto-escape unless :erb => { escape_html: true } is
+// configured — a scoped follow-up), <% %> is control flow. Unlike classic ERB
+// trim "<>", erubi keeps the trailing newline of a standalone `<%= … %>` line
+// (e.g. a `<%= yield %>` alone on its line in a layout), matching MRI Sinatra.
 //
 // Two view render paths land: an inline-String template (needs no filesystem)
 // and a :symbol template naming views/<sym>.erb (read through the File binding,
@@ -39,13 +46,8 @@ import (
 // (`erb :part` composed inside a view via a helper) and the :erb escape_html /
 // app-level `set :erb, layout:` engine options remain a scoped follow-up.
 
-// sinatraTrimMode is the ERB trim mode Sinatra renders with: Tilt::ERBTemplate
-// maps a nil/true :trim option (Sinatra's default) to "<>", so a line holding
-// only a code tag has both its surrounding newlines trimmed.
-const sinatraTrimMode = "<>"
-
 // sinatraEOutVar names the output buffer the compiled template appends to, matching
-// Tilt::ERBTemplate's default output variable.
+// Tilt::ErubiTemplate's default output variable.
 const sinatraEOutVar = "_erbout"
 
 // sinatraErb implements the `erb` view helper on a request context. template is
@@ -70,7 +72,11 @@ func (vm *VM) sinatraErb(sc *SinatraCtx, args []object.Value) object.Value {
 // non-nil, the yield block (used to expose the wrapped view to a layout's
 // `<%= yield %>`). It returns the rendered String.
 func (vm *VM) sinatraErbRender(sc *SinatraCtx, tmpl string, names []string, vals []object.Value, block *Proc) object.Value {
-	src, _, err := erbCompile(tmpl, erb.Options{TrimMode: sinatraTrimMode, EOutVar: sinatraEOutVar})
+	// ModeErubi: Sinatra 4.x renders ERB views through erubi (Tilt::ErubiTemplate),
+	// so go-ruby-erb compiles in erubi mode to stay byte-identical — notably a
+	// standalone `<%= yield %>` line keeps its trailing newline (classic ERB trim
+	// "<>" would drop it). The classic `require "erb"` binding stays in ModeERB.
+	src, _, err := erbCompile(tmpl, erb.Options{Mode: erb.ModeErubi, EOutVar: sinatraEOutVar})
 	if err != nil {
 		// go-ruby-erb never fails on a well-formed template (its err is reserved for
 		// genuinely malformed options, unreachable through this fixed-option call);

scripts/conformance/webapp/apps/sinatra_erb_oracle.rb

@@ -19,16 +19,13 @@
 # ruby 4.0.5). To regenerate the golden vector, run this file with `ruby` and the
 # sinatra gem installed.
 #
-# Trim note (a precisely-scoped go-ruby-erb LIBRARY follow-up, NOT a binding gap):
-# Sinatra 4.x maps :erb to Tilt::ErubiTemplate (erubi), whereas go-ruby-erb
-# mirrors MRI's ERB::Compiler. Rendered with trim "<>" (Tilt::ERBTemplate's own
-# default) the two agree byte-for-byte for single-line templates and idiomatic
-# multiline templates (a code-only `<% … %>` alone on its line). They diverge only
-# for the unusual line that BOTH opens a code block and ends with an expression
-# tag with trailing content (`<% each %>x <%= v %>`), where MRI ERB trims the
-# trailing newline and erubi keeps it. This fixture stays inside the agreeing
-# subset, so the diff is exact; full erubi trim-parity is tracked upstream in
-# go-ruby-erb.
+# Dialect note: Sinatra 4.x maps :erb to Tilt::ErubiTemplate (erubi), and rbgo now
+# renders Sinatra views through go-ruby-erb's ModeErubi, which reproduces
+# Erubi::Engine byte-for-byte. So this fixture exercises erubi's own whitespace
+# semantics directly — including a standalone `<%= yield %>` line (route
+# /l_standalone) whose trailing newline erubi keeps but classic ERB trim "<>" would
+# drop. That case was previously kept inline to dodge the classic-ERB divergence;
+# it is now asserted end-to-end, matching the real gem.
 
 require "sinatra/base"
 require "tmpdir"
@@ -93,13 +90,20 @@ class App < Sinatra::Base
 )
 # The default layout: surrounding markup with `<%= yield %>` interpolating the
 # wrapped view and an @ivar the before-filter set (the layout renders in the same
-# handler binding as the view). `yield` is kept inline (not alone on a line) so the
-# fixture stays inside the ERB/erubi trim-agreement subset the oracle relies on —
-# a standalone `<%= %>` line is the one documented go-ruby-erb LIBRARY divergence.
+# handler binding as the view). Here `yield` is kept inline within <main>…</main>.
 File.write(
   File.join(LVIEWS, "layout.erb"),
   "<!DOCTYPE html>\n<title>Site</title>\n<main><%= yield %></main>\n<footer>by <%= @who %></footer>\n"
 )
+# A layout with `<%= yield %>` STANDALONE on its own line — the erubi-specific case
+# the classic-ERB oracle used to avoid. Under erubi the yield line keeps its
+# trailing newline, so a blank-looking break appears between the wrapped view and
+# the footer; classic ERB trim "<>" would have swallowed that newline. Asserting it
+# byte-for-byte proves rbgo renders Sinatra views in erubi mode.
+File.write(
+  File.join(LVIEWS, "standalone.erb"),
+  "<header>H</header>\n<%= yield %>\n<footer>F</footer>\n"
+)
 # A custom layout selected with `layout: :alt`, using a render local (proving the
 # locals reach the layout, not just the view) around `<%= yield %>`.
 File.write(
@@ -140,6 +144,13 @@ class LApp < Sinatra::Base
     erb :card, { layout: "<wrap><%= yield %></wrap>\n" }, greeting: "In", items: %w[z]
   end
 
+  # A layout whose `<%= yield %>` stands ALONE on its own line: erubi keeps that
+  # line's trailing newline (classic ERB trim "<>" would drop it), so a bare
+  # newline separates the wrapped view from the footer. The newline-fidelity proof.
+  get "/l_standalone" do
+    erb :card, { layout: :standalone }, greeting: "So", items: %w[m]
+  end
+
   # A missing NAMED layout raises Errno::ENOENT (MRI eats the error only for the
   # implicit default layout, not an explicitly requested one).
   get "/l_missing_layout" do
@@ -176,6 +187,7 @@ class LApp < Sinatra::Base
   [LApp, { "REQUEST_METHOD" => "GET", "PATH_INFO" => "/l_inline", "QUERY_STRING" => "", "rack.url_scheme" => "http", "HTTP_HOST" => "ex" }],
   [LApp, { "REQUEST_METHOD" => "GET", "PATH_INFO" => "/l_missing_layout", "QUERY_STRING" => "", "rack.url_scheme" => "http", "HTTP_HOST" => "ex" }],
   [LApp, { "REQUEST_METHOD" => "GET", "PATH_INFO" => "/l_missing_view", "QUERY_STRING" => "", "rack.url_scheme" => "http", "HTTP_HOST" => "ex" }],
+  [LApp, { "REQUEST_METHOD" => "GET", "PATH_INFO" => "/l_standalone", "QUERY_STRING" => "", "rack.url_scheme" => "http", "HTTP_HOST" => "ex" }],
 ]
 
 REQS.each_with_index do |(app, env), i|

scripts/conformance/webapp/sinatra_erb_oracle_test.go

@@ -4,9 +4,11 @@ import "testing"
 
 // sinatraErbGem421Golden is the response dump of apps/sinatra_erb_oracle.rb
 // captured from the REAL `sinatra` gem 4.2.1 (MRI ruby 4.0.5) with its ERB view
-// engine: thirteen requests through the classic Sinatra::Base #call(env) adapter,
-// each rendering an ERB view (six inline/symbol templates, then seven exercising
-// the layout rule) and dumping [status, body]. This is the golden oracle for the
+// engine — which is erubi (Tilt::ErubiTemplate), the erubi gem 1.13.1: fourteen
+// requests through the classic Sinatra::Base #call(env) adapter, each rendering an
+// ERB view (six inline/symbol templates, then eight exercising the layout rule,
+// the last a standalone `<%= yield %>` line whose trailing newline erubi keeps but
+// classic ERB trim "<>" drops) and dumping [status, body]. This is the golden oracle for the
 // templating half of the Sinatra binding: rbgo, rendering through the bound
 // go-ruby-erb compiler, must reproduce it byte-for-byte. It is a captured constant
 // so the suite stays hermetic (no ruby, no gem, runs under qemu on every 64-bit
@@ -90,6 +92,16 @@ body<<Errno::ENOENT>>
 == req 12 ==
 status=200
 body<<Errno::ENOENT>>
+== req 13 ==
+status=200
+body<<<header>H</header>
+<h2>So World</h2>
+<ul>
+  <li>m</li>
+</ul>
+
+<footer>F</footer>
+>>
 `
 
 // TestSinatraErbGemOracle proves the Sinatra `erb` view helper is MRI-identical
@@ -101,9 +113,10 @@ body<<Errno::ENOENT>>
 // control flow, positional and options[:locals] locals, ERB trim behaviour, and
 // the layout rule (default views/layout.erb with `<%= yield %>` returning the
 // view, layout: false, a custom layout: :name, layout: true, an inline-String
-// layout, and the Errno::ENOENT a missing named layout / view raises) — all
-// rendered by rbgo (via the bound go-ruby-erb compiler, evaluated in the
-// handler's binding) exactly as by the reference gem.
+// layout, a layout with a standalone `<%= yield %>` line — the erubi
+// newline-fidelity case — and the Errno::ENOENT a missing named layout / view
+// raises) — all rendered by rbgo (via the bound go-ruby-erb compiler in erubi
+// mode, evaluated in the handler's binding) exactly as by the reference gem.
 func TestSinatraErbGemOracle(t *testing.T) {
 	if ok, detail := featureLoadable("sinatra/base"); !ok {
 		t.Fatalf("sinatra/base must be loadable for the ERB oracle: %s", detail)