Prefer 'final', only use 'override' where needed.

This helps documenting the code for the reader. For the compiler,
it might open devirtualization opportunities.

Document all the methods that can not be set `final` because they
are in fact overridden later. Mark as `// not yet final`.
This will be useful in future automated cleanups.

common/analysis/line_lint_rule.h

@@ -26,7 +26,7 @@ namespace verible {
 
 class LineLintRule : public LintRule {
  public:
-  ~LineLintRule() override = default;
+  ~LineLintRule() override = default;  // not yet final
 
   // Scans a single line during analysis.
   virtual void HandleLine(absl::string_view line) = 0;

common/analysis/syntax_tree_lint_rule.h

@@ -38,7 +38,7 @@ namespace verible {
 // top of the stack/back of vector.
 class SyntaxTreeLintRule : public LintRule {
  public:
-  ~SyntaxTreeLintRule() override = default;
+  ~SyntaxTreeLintRule() override = default;  // not yet final
 
   virtual void HandleLeaf(const SyntaxTreeLeaf &leaf,
                           const SyntaxTreeContext &context) {}

common/analysis/text_structure_lint_rule.h

@@ -38,7 +38,7 @@ namespace verible {
 
 class TextStructureLintRule : public LintRule {
  public:
-  ~TextStructureLintRule() override = default;
+  ~TextStructureLintRule() override = default;  // not yet final
 
   // Analyze text structure for violations.
   virtual void Lint(const TextStructureView &text_structure,

common/analysis/token_stream_lint_rule.h

@@ -26,7 +26,7 @@ namespace verible {
 
 class TokenStreamLintRule : public LintRule {
  public:
-  ~TokenStreamLintRule() override = default;
+  ~TokenStreamLintRule() override = default;  // not yet final
 
   // Scans a single token during analysis.
   virtual void HandleToken(const TokenInfo &token) = 0;

common/analysis/violation_handler.h

@@ -51,7 +51,7 @@ class ViolationPrinter : public ViolationHandler {
 
   void HandleViolations(
       const std::set<verible::LintViolationWithStatus>& violations,
-      absl::string_view base, absl::string_view path) override;
+      absl::string_view base, absl::string_view path) final;
 
  protected:
   std::ostream* const stream_;
@@ -68,7 +68,7 @@ class ViolationWaiverPrinter : public ViolationHandler {
 
   void HandleViolations(
       const std::set<verible::LintViolationWithStatus>& violations,
-      absl::string_view base, absl::string_view path) override;
+      absl::string_view base, absl::string_view path) final;
 
  protected:
   std::ostream* const message_stream_;

common/formatting/tree_unwrapper.h

@@ -52,7 +52,7 @@ class TreeUnwrapper : public TreeContextVisitor {
   TreeUnwrapper& operator=(const TreeUnwrapper&) = delete;
   TreeUnwrapper& operator=(TreeUnwrapper&&) = delete;
 
-  ~TreeUnwrapper() override = default;
+  ~TreeUnwrapper() override = default;  // not yet final.
 
   // Partitions the token stream (in text_structure_view_) into
   // unwrapped_lines_ by traversing the syntax tree representation.

common/lexer/flex_lexer_adapter.h

@@ -77,7 +77,7 @@ class FlexLexerAdapter : private CodeStreamHolder, protected L, public Lexer {
   const TokenInfo &GetLastToken() const final { return last_token_; }
 
   // Returns next token and updates its location.
-  const TokenInfo &DoNextToken() override {
+  const TokenInfo &DoNextToken() override {  // not yet final
     if (at_eof_) {
       // Do not call yylex(), because that will result in the fatal error:
       // "fatal flex scanner internal error--end of buffer missed"
@@ -108,7 +108,7 @@ class FlexLexerAdapter : private CodeStreamHolder, protected L, public Lexer {
   }
 
   // Restart lexer by pointing to new input stream, and reset all state.
-  void Restart(absl::string_view code) override {
+  void Restart(absl::string_view code) override {  // not yet final
     at_eof_ = false;
     code_ = code;
     code_stream_.str(std::string(code_));

common/lexer/token_stream_adapter_test.cc

@@ -38,7 +38,9 @@ class FakeTokenSequenceLexer : public Lexer, public FakeLexer {
 
   void Restart(absl::string_view) final {}
 
-  bool TokenIsError(const TokenInfo &) const override { return false; }
+  bool TokenIsError(const TokenInfo &) const override {  // not yet final.
+    return false;
+  }
 };
 
 TEST(MakeTokenGeneratorTest, Generate) {

common/text/text_structure_test.cc

@@ -363,7 +363,7 @@ class TextStructureViewInternalsTest : public TextStructureViewPublicTest {
   // modifications.  This is only appropriate for tests on private or protected
   // methods; public methods should always leave the structure in a consistent
   // state.
-  ~TextStructureViewInternalsTest() override { Clear(); }
+  ~TextStructureViewInternalsTest() override { Clear(); }  // not yet final
 };
 
 // Test that whole tree is returned with offset 0.

common/text/tree_context_visitor.h

@@ -30,8 +30,8 @@ class TreeContextVisitor : public SymbolVisitor {
   TreeContextVisitor() = default;
 
  protected:
-  void Visit(const SyntaxTreeLeaf &leaf) override {}
-  void Visit(const SyntaxTreeNode &node) override;
+  void Visit(const SyntaxTreeLeaf &leaf) override {}  // not yet final
+  void Visit(const SyntaxTreeNode &node) override;    // not yet final
 
   const SyntaxTreeContext &Context() const { return current_context_; }
 

verilog/tools/ls/verilog-language-server_test.cc

@@ -123,7 +123,7 @@ class VerilogLanguageServerTest : public ::testing::Test {
   // Sets up the testing environment - creates Language Server object and
   // sends textDocument/initialize request.
   // It stores the response in initialize_response field for further processing
-  void SetUp() override {
+  void SetUp() override {  // not yet final
     server_ = std::make_unique<VerilogLanguageServer>(
         [this](absl::string_view response) { response_stream_ << response; });
 
@@ -148,7 +148,7 @@ class VerilogLanguageServerTest : public ::testing::Test {
 
 class VerilogLanguageServerSymbolTableTest : public VerilogLanguageServerTest {
  public:
-  absl::Status InitializeCommunication() override {
+  absl::Status InitializeCommunication() final {
     json initialize_request = {
         {"jsonrpc", "2.0"},
         {"id", 1},
@@ -158,7 +158,7 @@ class VerilogLanguageServerSymbolTableTest : public VerilogLanguageServerTest {
   }
 
  protected:
-  void SetUp() override {
+  void SetUp() final {
     absl::SetFlag(&FLAGS_rules_config_search, true);
     root_dir = verible::file::JoinPath(
         ::testing::TempDir(),
@@ -168,7 +168,7 @@ class VerilogLanguageServerSymbolTableTest : public VerilogLanguageServerTest {
     VerilogLanguageServerTest::SetUp();
   }
 
-  void TearDown() override { std::filesystem::remove(root_dir); }
+  void TearDown() final { std::filesystem::remove(root_dir); }
 
   // path to the project
   std::string root_dir;