Fix cross-reference resolution for constants (#1539)

This PR resolves #1011 by ensuring that constant names ~~with `::` (e.g.
`::CONSTANT_NAME`) can be used to find constants in contexts~~ can be
resolved by `RDoc::CrossReference#resolve_local_symbol` (originally
named `resolve_method`). Please note that the darkfish and aliki themes
do not display links for constants in the constants section (just the
names of the constants in a description list), so the changes in this PR
just make it possible to cross reference constants. I will create a
separate PR to propose changes to the themes.

Author: extern-c

lib/rdoc/cross_reference.rb

@@ -132,47 +132,56 @@ def initialize(context)
   end
 
   ##
-  # Returns a method reference to +name+.
+  # Returns a method, attribute or constant reference to +name+
+  # if it exists in the containing context object. It returns
+  # nil otherwise.
+  #
+  # For example, this method would decompose name = 'A::CONSTANT' into a
+  # container object A and a symbol 'CONSTANT', and it would try to find
+  # 'CONSTANT' in A.
 
-  def resolve_method(name)
+  def resolve_local_symbol(name)
     ref = nil
+    type = nil
+    container = nil
 
-    if /#{CLASS_REGEXP_STR}([.#]|::)#{METHOD_REGEXP_STR}/o =~ name then
+    case name
+    when /#{CLASS_REGEXP_STR}::([A-Z]\w*)\z/o then
+      symbol = $2
+      container = @context.find_symbol_module($1)
+    when /#{CLASS_REGEXP_STR}([.#]|::)#{METHOD_REGEXP_STR}/o then
       type = $2
       if '.' == type # will find either #method or ::method
-        method = $3
+        symbol = $3
       else
-        method = "#{type}#{$3}"
+        symbol = "#{type}#{$3}"
       end
       container = @context.find_symbol_module($1)
-    elsif /^([.#]|::)#{METHOD_REGEXP_STR}/o =~ name then
+    when /^([.#]|::)#{METHOD_REGEXP_STR}/o then
       type = $1
       if '.' == type
-        method = $2
+        symbol = $2
       else
-        method = "#{type}#{$2}"
+        symbol = "#{type}#{$2}"
       end
       container = @context
-    else
-      type = nil
-      container = nil
     end
 
     if container then
       unless RDoc::TopLevel === container then
         if '.' == type then
-          if 'new' == method then # AnyClassName.new will be class method
-            ref = container.find_local_symbol method
-            ref = container.find_ancestor_local_symbol method unless ref
+          if 'new' == symbol then # AnyClassName.new will be class method
+            ref = container.find_local_symbol symbol
+            ref = container.find_ancestor_local_symbol symbol unless ref
           else
-            ref = container.find_local_symbol "::#{method}"
-            ref = container.find_ancestor_local_symbol "::#{method}" unless ref
-            ref = container.find_local_symbol "##{method}" unless ref
-            ref = container.find_ancestor_local_symbol "##{method}" unless ref
+            ref = container.find_local_symbol "::#{symbol}"
+            ref = container.find_ancestor_local_symbol "::#{symbol}" unless ref
+            ref = container.find_local_symbol "##{symbol}" unless ref
+            ref = container.find_ancestor_local_symbol "##{symbol}" unless ref
           end
         else
-          ref = container.find_local_symbol method
-          ref = container.find_ancestor_local_symbol method unless ref
+          ref = container.find_local_symbol symbol
+          ref = container.find_ancestor_local_symbol symbol unless ref
         end
       end
     end
@@ -197,7 +206,7 @@ def resolve(name, text)
             @context.find_symbol name
           end
 
-    ref = resolve_method name unless ref
+    ref = resolve_local_symbol name unless ref
 
     # Try a page name
     ref = @store.page name if not ref and name =~ /^[\w.\/]+$/

test/rdoc/rdoc_cross_reference_test.rb

@@ -157,6 +157,12 @@ def test_resolve_method
     assert_ref @c2_c3_m, '::C2::C3#m(*)'
   end
 
+  def test_resolve_constant
+    assert_ref @c1_const, 'CONST'
+    assert_ref @c1_const, 'C1::CONST'
+    assert_ref @c1_const, 'C12::CONST'
+  end
+
   def test_resolve_the_same_name_in_instance_and_class_method
     assert_ref @c9_a_i_foo, 'C9::A#foo'
     assert_ref @c9_a_c_bar, 'C9::A::bar'

test/rdoc/rdoc_store_test.rb

@@ -163,7 +163,7 @@ def test_add_file_relative
 
   def test_all_classes_and_modules
     expected = %w[
-      C1 C10 C10::C11 C11 C2 C2::C3 C2::C3::H1 C3 C3::H1 C3::H2 C4 C4::C4 C5 C5::C1 C6 C7 C8 C9 C9::A C9::B
+      C1 C10 C10::C11 C11 C12 C2 C2::C3 C2::C3::H1 C3 C3::H1 C3::H2 C4 C4::C4 C5 C5::C1 C6 C7 C8 C9 C9::A C9::B
       Child
       M1 M1::M2
       Object
@@ -219,7 +219,7 @@ def test_class_path
 
   def test_classes
     expected = %w[
-      C1 C10 C10::C11 C11 C2 C2::C3 C2::C3::H1 C3 C3::H1 C3::H2 C4 C4::C4 C5 C5::C1 C6 C7 C8 C9 C9::A C9::B
+      C1 C10 C10::C11 C11 C12 C2 C2::C3 C2::C3::H1 C3 C3::H1 C3::H2 C4 C4::C4 C5 C5::C1 C6 C7 C8 C9 C9::A C9::B
       Child
       Object
       Parent

test/rdoc/xref_data.rb

@@ -145,6 +145,9 @@ class C11
 def C11
 end
 
+class C12 < C1
+end
+
 module M1
   def m
   end

test/rdoc/xref_test_case.rb

@@ -33,6 +33,7 @@ def setup
     @c1__m    = @c1.find_class_method_named 'm' # C1::m
     @c1_m     = @c1.find_instance_method_named 'm'  # C1#m
     @c1_plus  = @c1.find_instance_method_named '+'
+    @c1_const = @c1.find_constant_named 'CONST'
 
     @c2    = @xref_data.find_module_named 'C2'
     @c2_a  = @c2.method_list.last