Save links to the source in the database

They are not generated into the html output yet.

- Definitions with comments are preferred (including in an overload set)
  of multiple definitions.
- If the comment is not on the definition, the definition is still
  preferred.
- Otherwise, the comment location is preferred.
- Lastly, any given location will do.

subdoc/CMakeLists.txt

@@ -145,6 +145,7 @@ if(${SUBSPACE_BUILD_TESTS})
         "tests/methods_unittest.cc"
         "tests/namespaces_unittest.cc"
         "tests/records_unittest.cc"
+        "tests/source_link_unittest.cc"
         "tests/styles_unittest.cc"
         "tests/type_unittest.cc"
         "tests/self_name_replace_unittest.cc"

subdoc/lib/database.h

@@ -60,6 +60,24 @@ using FoundName = sus::Choice<sus_choice_types(
     (FoundNameTag::Field, const FieldElement&),
     (FoundNameTag::Macro, const MacroElement&))>;
 
+struct SourceLink {
+  enum Quality {
+    UnknownLocation,
+    CommentLocation,
+    DefinitionLocation,
+    CommentAndDefinitionLocation,
+  };
+  Quality quality;
+  std::string file_path;
+  u32 line;
+
+  friend std::weak_ordering operator<=>(const SourceLink& lhs,
+                                        const SourceLink& rhs) noexcept {
+    return lhs.quality <=> rhs.quality;
+  }
+};
+static_assert(sus::cmp::Ord<SourceLink>);
+
 struct Comment {
   Comment() = default;
   Comment(std::string text, std::string begin_loc, DocAttributes attrs)
@@ -93,6 +111,7 @@ struct CommentElement {
   Comment comment;
   std::string name;
   u32 sort_key;
+  sus::Option<SourceLink> source_link;
 
   /// Used during visit to determine if a comment has already been found and
   /// applied to the element.

subdoc/lib/run.cc

@@ -24,7 +24,8 @@
 namespace subdoc {
 
 sus::Result<Database, DiagnosticResults> run_test(
-    std::string content, sus::Slice<std::string> command_line_args,
+    std::string pretend_file_name, std::string content,
+    sus::Slice<std::string> command_line_args,
     const RunOptions& options) noexcept {
   auto join_args = std::string();
   for (const std::string& a : command_line_args) {
@@ -40,9 +41,11 @@ sus::Result<Database, DiagnosticResults> run_test(
   }
 
   auto vfs = llvm::IntrusiveRefCntPtr(new llvm::vfs::InMemoryFileSystem());
-  vfs->addFile("test.cc", 0, llvm::MemoryBuffer::getMemBuffer(content));
+  vfs->addFile(pretend_file_name, 0, llvm::MemoryBuffer::getMemBuffer(content));
 
-  return run_files(*comp_db, sus::Vec<std::string>("test.cc"), std::move(vfs), options);
+  return run_files(*comp_db,
+                   sus::Vec<std::string>(sus::move(pretend_file_name)),
+                   std::move(vfs), options);
 }
 
 struct DiagnosticTracker : public clang::TextDiagnosticPrinter {
@@ -109,8 +112,8 @@ sus::Result<Database, DiagnosticResults> run_files(
   tool.appendArgumentsAdjuster(adj);
 
   auto cx = VisitCx(options);
-  auto docs_db =
-      Database(Comment(sus::clone(options.project_overview_text), "", DocAttributes()));
+  auto docs_db = Database(
+      Comment(sus::clone(options.project_overview_text), "", DocAttributes()));
   auto visitor_factory = VisitorFactory(cx, docs_db, num_files);
 
   i32 run_value = sus::move(tool).run(&visitor_factory);

subdoc/lib/run.h

@@ -32,7 +32,8 @@ struct DiagnosticResults {
 static_assert(sus::mem::Move<DiagnosticResults>);
 
 sus::Result<Database, DiagnosticResults> run_test(
-    std::string content, sus::Slice<std::string> command_line_args,
+    std::string pretend_file_name, std::string content,
+    sus::Slice<std::string> command_line_args,
     const RunOptions& options) noexcept;
 
 sus::Result<Database, DiagnosticResults> run_files(