Run clang-tidy over toolchain code. (#3105)

Amongst other changes, this removes the implicit StringRef cast in
formatter code due to google-explicit-constructor. Only one line of code
relied on the implicit cast, and style says "Do not define implicit
conversions."
(https://google.github.io/styleguide/cppguide.html#Implicit_Conversions).

---------

Co-authored-by: Richard Smith <richard@metafoo.co.uk>

toolchain/diagnostics/diagnostic_emitter.h

@@ -67,7 +67,7 @@ struct DiagnosticMessage {
       llvm::StringLiteral format, llvm::SmallVector<llvm::Any> format_args,
       std::function<std::string(const DiagnosticMessage&)> format_fn)
       : kind(kind),
-        location(std::move(location)),
+        location(location),
         format(format),
         format_args(std::move(format_args)),
         format_fn(std::move(format_fn)) {}

toolchain/lexer/token_kind.cpp

@@ -107,7 +107,7 @@ auto TokenKind::fixed_spelling() const -> llvm::StringRef {
 auto TokenKind::expected_parse_tree_size() const -> int {
   static constexpr int8_t Table[] = {
 #define CARBON_TOKEN(Name) 1,
-#define CARBON_TOKEN_WITH_VIRTUAL_NODE(size) 1 + size
+#define CARBON_TOKEN_WITH_VIRTUAL_NODE(size) 2,
 #include "toolchain/lexer/token_kind.def"
   };
   return Table[AsInt()];

toolchain/lexer/tokenized_buffer_test.cpp

@@ -28,7 +28,6 @@ using ::testing::_;
 using ::testing::ElementsAre;
 using ::testing::Eq;
 using ::testing::HasSubstr;
-using ::testing::StrEq;
 
 class LexerTest : public ::testing::Test {
  protected:

toolchain/semantics/semantics_context.cpp

@@ -640,8 +640,9 @@ auto SemanticsContext::GetUnqualifiedType(SemanticsTypeId type_id)
     -> SemanticsTypeId {
   SemanticsNode type_node =
       semantics_ir_->GetNode(semantics_ir_->GetTypeAllowBuiltinTypes(type_id));
-  if (type_node.kind() == SemanticsNodeKind::ConstType)
+  if (type_node.kind() == SemanticsNodeKind::ConstType) {
     return type_node.GetAsConstType();
+  }
   return type_id;
 }
 

toolchain/semantics/semantics_context.h

@@ -92,7 +92,7 @@ class SemanticsContext {
   // reconvergence of control flow, and pushes the new block onto the node
   // block stack.
   auto AddConvergenceBlockAndPush(
-      ParseTree::Node parse_tree,
+      ParseTree::Node parse_node,
       std::initializer_list<SemanticsNodeBlockId> blocks) -> void;
 
   // Adds branches from the given list of blocks and values to a new block, for

toolchain/semantics/semantics_ir_formatter.cpp

@@ -22,10 +22,13 @@ namespace {
 //   type to distinguish.
 class NodeNamer {
  public:
-  enum class ScopeIndex : int {
+  // int32_t matches the input value size.
+  // NOLINTNEXTLINE(performance-enum-size)
+  enum class ScopeIndex : int32_t {
     None = -1,
     Package = 0,
   };
+  static_assert(sizeof(ScopeIndex) == sizeof(SemanticsFunctionId));
 
   NodeNamer(const TokenizedBuffer& tokenized_buffer,
             const ParseTree& parse_tree, const SemanticsIR& semantics_ir)
@@ -68,7 +71,7 @@ class NodeNamer {
 
   // Returns the scope index corresponding to a function.
   auto GetScopeFor(SemanticsFunctionId fn_id) -> ScopeIndex {
-    return ScopeIndex(fn_id.index + 1);
+    return static_cast<ScopeIndex>(fn_id.index + 1);
   }
 
   // Returns the IR name to use for a function.
@@ -76,7 +79,7 @@ class NodeNamer {
     if (!fn_id.is_valid()) {
       return "invalid";
     }
-    return GetScopeInfo(GetScopeFor(fn_id)).name;
+    return GetScopeInfo(GetScopeFor(fn_id)).name.str();
   }
 
   // Returns the IR name to use for a node, when referenced from a given scope.
@@ -145,8 +148,6 @@ class NodeNamer {
         return value->first();
       }
 
-      operator llvm::StringRef() const { return str(); }
-
       auto SetFallback(Name name) -> void { value_->second.fallback = name; }
 
       auto SetAmbiguous() -> void { value_->second.ambiguous = true; }
@@ -239,7 +240,7 @@ class NodeNamer {
   };
 
   auto GetScopeInfo(ScopeIndex scope_idx) -> Scope& {
-    return scopes[(int)scope_idx];
+    return scopes[static_cast<int>(scope_idx)];
   }
 
   auto AddBlockLabel(ScopeIndex scope_idx, SemanticsNodeBlockId block_id,
@@ -251,7 +252,8 @@ class NodeNamer {
     }
 
     if (parse_node == ParseTree::Node::Invalid) {
-      if (auto& block = semantics_ir_.GetNodeBlock(block_id); !block.empty()) {
+      if (const auto& block = semantics_ir_.GetNodeBlock(block_id);
+          !block.empty()) {
         parse_node = semantics_ir_.GetNode(block.front()).parse_node();
       }
     }
@@ -524,8 +526,9 @@ class SemanticsIRFormatter {
   // are never referenced themselves.
   // TODO: Include BindName nodes in the output if we start referring to them.
   template <>
-  auto FormatInstruction<SemanticsNode::BindName>(SemanticsNodeId,
-                                                  SemanticsNode) -> void {}
+  auto FormatInstruction<SemanticsNode::BindName>(SemanticsNodeId /*node_id*/,
+                                                  SemanticsNode /*node*/)
+      -> void {}
 
   template <>
   auto FormatInstructionRHS<SemanticsNode::BlockArg>(SemanticsNode node)
@@ -535,7 +538,7 @@ class SemanticsIRFormatter {
   }
 
   template <>
-  auto FormatInstruction<SemanticsNode::BranchIf>(SemanticsNodeId,
+  auto FormatInstruction<SemanticsNode::BranchIf>(SemanticsNodeId /*node_id*/,
                                                   SemanticsNode node) -> void {
     if (!in_terminator_sequence) {
       out_ << "  ";
@@ -550,9 +553,8 @@ class SemanticsIRFormatter {
   }
 
   template <>
-  auto FormatInstruction<SemanticsNode::BranchWithArg>(SemanticsNodeId,
-                                                       SemanticsNode node)
-      -> void {
+  auto FormatInstruction<SemanticsNode::BranchWithArg>(
+      SemanticsNodeId /*node_id*/, SemanticsNode node) -> void {
     if (!in_terminator_sequence) {
       out_ << "  ";
     }
@@ -566,7 +568,7 @@ class SemanticsIRFormatter {
   }
 
   template <>
-  auto FormatInstruction<SemanticsNode::Branch>(SemanticsNodeId,
+  auto FormatInstruction<SemanticsNode::Branch>(SemanticsNodeId /*node_id*/,
                                                 SemanticsNode node) -> void {
     if (!in_terminator_sequence) {
       out_ << "  ";
@@ -596,9 +598,8 @@ class SemanticsIRFormatter {
 
   // StructTypeFields are formatted as part of their StructType.
   template <>
-  auto FormatInstruction<SemanticsNode::StructTypeField>(SemanticsNodeId,
-                                                         SemanticsNode)
-      -> void {}
+  auto FormatInstruction<SemanticsNode::StructTypeField>(
+      SemanticsNodeId /*node_id*/, SemanticsNode /*node*/) -> void {}
 
   template <>
   auto FormatInstructionRHS<SemanticsNode::StructType>(SemanticsNode node)
@@ -616,7 +617,7 @@ class SemanticsIRFormatter {
     out_ << "}";
   }
 
-  auto FormatArgs(SemanticsNode::NoArgs) -> void {}
+  auto FormatArgs(SemanticsNode::NoArgs /*unused*/) -> void {}
 
   template <typename Arg1>
   auto FormatArgs(Arg1 arg) -> void {