FIX: proper details / summary excerpt (discourse#30229)

It doesn't make much sense to have the content of a `<details>` in an excerpt so I replaced them with "▶ summary" instead.

That way, they can't be (ab)used in user cards for example.

Reference - https://meta.discourse.org/t/335094

lib/excerpt_parser.rb

@@ -24,8 +24,6 @@ def initialize(length, options = nil)
     @start_excerpt = false
     @start_hashtag_icon = false
     @in_details_depth = 0
-    @summary_contents = +""
-    @detail_contents = +""
   end
 
   def self.get_excerpt(html, length, options)
@@ -127,12 +125,11 @@ def start_element(name, attributes = [])
         include_tag(name, attributes)
       end
     when "details"
-      @detail_contents = +"" if @in_details_depth == 0
       @in_details_depth += 1
     when "summary"
       if @in_details_depth == 1 && !@in_summary
-        @summary_contents = +""
         @in_summary = true
+        characters("▶ ", truncate: false, count_it: false, encode: false)
       end
     when "svg"
       attributes = Hash[*attributes.flatten]
@@ -162,29 +159,6 @@ def end_element(name)
       @in_quote = false
     when "details"
       @in_details_depth -= 1
-      if @in_details_depth == 0
-        @summary_contents = clean(@summary_contents)
-        @detail_contents = clean(@detail_contents)
-
-        if @current_length + @summary_contents.length >= @length
-          characters(
-            @summary_contents,
-            encode: false,
-            before_string: "<details class='disabled'><summary>",
-            after_string: "</summary></details>",
-          )
-        else
-          characters(
-            @summary_contents,
-            truncate: false,
-            encode: false,
-            before_string: "<details><summary>",
-            after_string: "</summary>",
-          )
-
-          characters(@detail_contents, encode: false, after_string: "</details>")
-        end
-      end
     when "summary"
       @in_summary = false if @in_details_depth == 1
     when "div", "span"
@@ -210,18 +184,10 @@ def characters(
     before_string: nil,
     after_string: nil
   )
-    return if @in_quote
+    return if @in_quote || @in_details_depth > 1 || (@in_details_depth == 1 && !@in_summary)
 
     # we call length on this so might as well ensure we have a string
     string = string.to_s
-    if @in_details_depth > 0
-      if @in_summary
-        @summary_contents << string
-      else
-        @detail_contents << string
-      end
-      return
-    end
 
     @excerpt << before_string if before_string
 

spec/lib/excerpt_parser_spec.rb

@@ -6,43 +6,18 @@
   it "handles nested <details> blocks" do
     html = <<~HTML.strip
       <details>
-      <summary>
-      FOO</summary>
-      <details>
-      <summary>
-      BAR</summary>
-      <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Fusce ultrices, ex bibendum vestibulum vestibulum, mi velit pulvinar risus, sed consequat eros libero in eros. Fusce luctus mattis mauris, vitae semper lorem sodales quis. Donec pellentesque lacus ac ante aliquam, tincidunt iaculis risus interdum. In ullamcorper cursus massa ut lacinia. Donec quis diam finibus, rutrum odio eu, maximus leo. Nulla facilisi. Nullam suscipit quam et bibendum sagittis. Praesent sollicitudin neque at luctus ornare. Maecenas tristique dapibus risus, ac dictum ipsum gravida aliquam. Phasellus vehicula eu arcu sed imperdiet. Vestibulum ornare eros a nisi faucibus vehicula. Quisque congue placerat nulla, nec finibus nulla ultrices vitae. Quisque ac mi sem. Curabitur eu porttitor justo. Etiam dignissim in orci iaculis congue. Donec tempus cursus orci, a placerat elit varius nec.</p>
-      </details>
+        <summary>FOO</summary>
+        <details>
+          <summary>BAR</summary>
+          <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit.</p>
+        </details>
       </details>
     HTML
 
-    expect(ExcerptParser.get_excerpt(html, 50, {})).to match_html <<~HTML
-      <details><summary>FOO</summary>BAR
-      Lorem ipsum dolor sit amet, consectetur adi&hellip;</details>
-    HTML
-
-    expect(ExcerptParser.get_excerpt(html, 6, {})).to match_html(
-      "<details><summary>FOO</summary>BAR&hellip;</details>",
-    )
-    expect(ExcerptParser.get_excerpt(html, 3, {})).to match_html(
-      '<details class="disabled"><summary>FOO</summary></details>',
-    )
-  end
-
-  it "respects length parameter for <details> block" do
-    html = "<details><summary>foo</summary><p>bar</p></details>"
-    expect(ExcerptParser.get_excerpt(html, 100, {})).to match_html(
-      "<details><summary>foo</summary>bar</details>",
-    )
-    expect(ExcerptParser.get_excerpt(html, 5, {})).to match_html(
-      "<details><summary>foo</summary>ba&hellip;</details>",
-    )
-    expect(ExcerptParser.get_excerpt(html, 3, {})).to match_html(
-      '<details class="disabled"><summary>foo</summary></details>',
-    )
-    expect(ExcerptParser.get_excerpt(html, 2, {})).to match_html(
-      '<details class="disabled"><summary>fo&hellip;</summary></details>',
-    )
+    expect(ExcerptParser.get_excerpt(html, 50, {})).to match_html "▶ FOO"
+    expect(ExcerptParser.get_excerpt(html, 6, {})).to match_html "▶ FOO"
+    expect(ExcerptParser.get_excerpt(html, 3, {})).to match_html "▶ FOO"
+    expect(ExcerptParser.get_excerpt(html, 2, {})).to match_html "▶ FO&hellip;"
   end
 
   it "allows <svg> with <use> inside for icons when keep_svg is true" do

spec/lib/pretty_text_spec.rb

@@ -923,16 +923,10 @@ def cook(*args)
         ).to eq("![car](http://cnn.com/a.gif)")
       end
 
-      it "should keep details if too long" do
+      it "replaces details / summary with the summary" do
         expect(
           PrettyText.excerpt("<details><summary>expand</summary><p>hello</p></details>", 6),
-        ).to match_html "<details class='disabled'><summary>expand</summary></details>"
-      end
-
-      it "doesn't disable details if short enough" do
-        expect(
-          PrettyText.excerpt("<details><summary>expand</summary><p>hello</p></details>", 60),
-        ).to match_html "<details><summary>expand</summary>hello</details>"
+        ).to match_html "▶ expand"
       end
 
       it "should remove meta information" do