Add flag to optionally enable libxml2

Doing so will enable doc generation sanitization
With it disabled, a warning is printed to STDERR when generating docs

Makefile

@@ -36,11 +36,13 @@ target ?=       ## Cross-compilation target
 interpreter ?=  ## Enable interpreter feature
 check ?=        ## Enable only check when running format
 order ?=random  ## Enable order for spec execution (values: "default" | "random" | seed number)
+libxml2 ?=      ## Enable LibXML2 support in the compiler itself
+                ## (necessary for doc generation sanitization)
 
 O := .build
 SOURCES := $(shell find src -name '*.cr')
 SPEC_SOURCES := $(shell find spec -name '*.cr')
-override FLAGS += -D strict_multi_assign -D preview_overload_order $(if $(release),--release )$(if $(stats),--stats )$(if $(progress),--progress )$(if $(threads),--threads $(threads) )$(if $(debug),-d )$(if $(static),--static )$(if $(LDFLAGS),--link-flags="$(LDFLAGS)" )$(if $(target),--cross-compile --target $(target) )$(if $(interpreter),,-Dwithout_interpreter )
+override FLAGS += -D strict_multi_assign -D preview_overload_order $(if $(release),--release )$(if $(stats),--stats )$(if $(progress),--progress )$(if $(threads),--threads $(threads) )$(if $(debug),-d )$(if $(static),--static )$(if $(LDFLAGS),--link-flags="$(LDFLAGS)" )$(if $(target),--cross-compile --target $(target) )$(if $(interpreter),,-Dwithout_interpreter )$(if $(libxml2),,-Dwithout_libxml2)
 SPEC_WARNINGS_OFF := --exclude-warnings spec/std --exclude-warnings spec/compiler --exclude-warnings spec/primitives
 SPEC_FLAGS := $(if $(verbose),-v )$(if $(junit_output),--junit_output $(junit_output) )$(if $(order),--order=$(order) )
 CRYSTAL_CONFIG_LIBRARY_PATH := '$$ORIGIN/../lib/crystal'

Makefile.win

@@ -36,6 +36,8 @@ target ?=       ## Cross-compilation target
 interpreter ?=  ## Enable interpreter feature
 check ?=        ## Enable only check when running format
 order ?=random  ## Enable order for spec execution (values: "default" | "random" | seed number)
+libxml2 ?=      ## Enable LibXML2 support in the compiler itself 
+                ## (necessary for doc generation sanitization)
 
 MAKEFLAGS += --no-builtin-rules
 .SUFFIXES:
@@ -57,7 +59,7 @@ RMDIR = if exist $1 rd /S /Q $1
 O := .build
 SOURCES := $(call GLOB,src\\*.cr)
 SPEC_SOURCES := $(call GLOB,spec\\*.cr)
-override FLAGS += -D strict_multi_assign -D preview_overload_order $(if $(release),--release )$(if $(stats),--stats )$(if $(progress),--progress )$(if $(threads),--threads $(threads) )$(if $(debug),-d )$(if $(static),--static )$(if $(LDFLAGS),--link-flags="$(LDFLAGS)" )$(if $(target),--cross-compile --target $(target) )$(if $(interpreter),,-Dwithout_interpreter )
+override FLAGS += -D strict_multi_assign -D preview_overload_order $(if $(release),--release )$(if $(stats),--stats )$(if $(progress),--progress )$(if $(threads),--threads $(threads) )$(if $(debug),-d )$(if $(static),--static )$(if $(LDFLAGS),--link-flags="$(LDFLAGS)" )$(if $(target),--cross-compile --target $(target) )$(if $(interpreter),,-Dwithout_interpreter )$(if $(libxml2),,-Dwithout_libxml2 )
 SPEC_WARNINGS_OFF := --exclude-warnings spec\std --exclude-warnings spec\compiler --exclude-warnings spec\primitives
 SPEC_FLAGS := $(if $(verbose),-v )$(if $(junit_output),--junit_output $(junit_output) )$(if $(order),--order=$(order) )
 CRYSTAL_CONFIG_LIBRARY_PATH := $$ORIGIN\lib

spec/compiler/crystal/tools/doc/doc_renderer_spec.cr

@@ -374,33 +374,35 @@ describe Doc::MarkdDocRenderer do
     HTML
   end
 
-  describe "renders html with sanitization" do
-    it_renders nil, %(<h1 align="center">Foo</h1>), %(<h1>Foo</h1>)
-    it_renders nil, %(<script>alert("hello world")</script>), %()
-    it_renders nil, %(<p style="font-size: 100px">example text</p></div>), %(<p>example text</p>)
-
-    it_renders nil, %(```crystal\n# <script>alert("hello world")</script>\n```),
-      %(<pre><code class="language-crystal"><span class="c"># &lt;script&gt;alert(&quot;hello world&quot;)&lt;/script&gt;</span></code></pre>)
-  end
-
-  describe "still renders tables despite sanitization" do
-    table_mkdn = <<-HTML
-      <table>
-        <tr>
-          <th>column 1</th>
-          <th>column 2</th>
-        </tr>
-        <tr>
-          <td>data 1</td>
-          <td>data 2</td>
-        </tr>
-        <tr>
-          <td>data 3</td>
-          <td>data 4</td>
-        </tr>
-      </table>
-    HTML
-
-    it_renders nil, table_mkdn, table_mkdn
-  end
+  {% if !flag?(:without_libxml2) %}
+    describe "renders html with sanitization" do
+      it_renders nil, %(<h1 align="center">Foo</h1>), %(<h1>Foo</h1>)
+      it_renders nil, %(<script>alert("hello world")</script>), %()
+      it_renders nil, %(<p style="font-size: 100px">example text</p></div>), %(<p>example text</p>)
+
+      it_renders nil, %(```crystal\n# <script>alert("hello world")</script>\n```),
+        %(<pre><code class="language-crystal"><span class="c"># &lt;script&gt;alert(&quot;hello world&quot;)&lt;/script&gt;</span></code></pre>)
+    end
+
+    describe "still renders tables despite sanitization" do
+      table_mkdn = <<-HTML
+        <table>
+          <tr>
+            <th>column 1</th>
+            <th>column 2</th>
+          </tr>
+          <tr>
+            <td>data 1</td>
+            <td>data 2</td>
+          </tr>
+          <tr>
+            <td>data 3</td>
+            <td>data 4</td>
+          </tr>
+        </table>
+      HTML
+
+      it_renders nil, table_mkdn, table_mkdn
+    end
+  {% end %}
 end

src/compiler/crystal/command/docs.cr

@@ -119,6 +119,10 @@ class Crystal::Command
       STDERR.puts "Couldn't determine version from git or shard.yml, please provide --project-version option"
     end
 
+    if Crystal::Doc::MarkdDocRenderer::SANITIZER.nil?
+      STDERR.puts "Crystal built without LibXML2 support, documentation sanitization disabled"
+    end
+
     unless project_info.name? && project_info.version?
       abort
     end

src/compiler/crystal/tools/doc/markd_doc_renderer.cr

@@ -1,7 +1,14 @@
-require "sanitize"
+{% if !flag?(:without_libxml2) %}
+  require "sanitize"
+{% end %}
 
 class Crystal::Doc::MarkdDocRenderer < Markd::HTMLRenderer
-  SANITIZER = Sanitize::Policy::HTMLSanitizer.common
+  {% if !flag?(:without_libxml2) %}
+    SANITIZER = Sanitize::Policy::HTMLSanitizer.common
+  {% else %}
+    SANITIZER = nil
+  {% end %}
+
   @anchor_map = Hash(String, Int32).new(0)
 
   def initialize(@type : Crystal::Doc::Type, options)
@@ -179,6 +186,10 @@ class Crystal::Doc::MarkdDocRenderer < Markd::HTMLRenderer
   end
 
   def sanitize(node : Markd::Node) : String
-    SANITIZER.process(node.text)
+    {% if !flag?(:without_libxml2) %}
+      SANITIZER.process(node.text)
+    {% else %}
+      node.text
+    {% end %}
   end
 end