Move trace banners to driver and trace intermediate state. (#2443)

Printing intermediate state should be helpful to be able to examine the input when debugging later steps.

Intermediate state is hard to trace from the individual libraries since they don't know whether `dump` is going to print the state, so this moves some trace logic into the driver which is better equipped to make the decision.

toolchain/driver/BUILD

@@ -15,6 +15,7 @@ cc_library(
     hdrs = ["driver.h"],
     textual_hdrs = ["flags.def"],
     deps = [
+        "//common:vlog",
         "//toolchain/diagnostics:diagnostic_emitter",
         "//toolchain/diagnostics:sorting_diagnostic_consumer",
         "//toolchain/lexer:tokenized_buffer",

toolchain/driver/driver.cpp

@@ -4,6 +4,7 @@
 
 #include "toolchain/driver/driver.h"
 
+#include "common/vlog.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringRef.h"
@@ -148,7 +149,9 @@ auto Driver::RunDumpSubcommand(DiagnosticConsumer& consumer,
     return false;
   }
 
+  CARBON_VLOG() << "*** SourceBuffer::CreateFromFile ***\n";
   auto source = SourceBuffer::CreateFromFile(input_file_name);
+  CARBON_VLOG() << "*** SourceBuffer::CreateFromFile done ***\n";
   if (!source) {
     error_stream_ << "ERROR: Unable to open input source file: ";
     llvm::handleAllErrors(source.takeError(),
@@ -159,29 +162,39 @@ auto Driver::RunDumpSubcommand(DiagnosticConsumer& consumer,
     return false;
   }
 
+  CARBON_VLOG() << "*** TokenizedBuffer::Lex ***\n";
   auto tokenized_source = TokenizedBuffer::Lex(*source, consumer);
+  CARBON_VLOG() << "*** TokenizedBuffer::Lex done ***\n";
   if (dump_mode == DumpMode::TokenizedBuffer) {
+    CARBON_VLOG() << "Finishing output.";
     consumer.Flush();
     tokenized_source.Print(output_stream_);
     return !tokenized_source.has_errors();
   }
+  CARBON_VLOG() << tokenized_source;
 
+  CARBON_VLOG() << "*** ParseTree::Parse ***\n";
   auto parse_tree = ParseTree::Parse(tokenized_source, consumer, vlog_stream_);
+  CARBON_VLOG() << "*** ParseTree::Parse done ***\n";
   if (dump_mode == DumpMode::ParseTree) {
     consumer.Flush();
     parse_tree.Print(output_stream_, parse_tree_preorder);
     return !tokenized_source.has_errors() && !parse_tree.has_errors();
   }
+  CARBON_VLOG() << parse_tree;
 
   const SemanticsIR builtin_ir = SemanticsIR::MakeBuiltinIR();
+  CARBON_VLOG() << "*** SemanticsIR::MakeFromParseTree ***\n";
   const SemanticsIR semantics_ir = SemanticsIR::MakeFromParseTree(
       builtin_ir, tokenized_source, parse_tree, consumer, vlog_stream_);
+  CARBON_VLOG() << "*** SemanticsIR::MakeFromParseTree done ***\n";
   if (dump_mode == DumpMode::SemanticsIR) {
     consumer.Flush();
     semantics_ir.Print(output_stream_);
     // TODO: Return false when SemanticsIR has errors (not supported right now).
     return !tokenized_source.has_errors() && !parse_tree.has_errors();
   }
+  CARBON_VLOG() << semantics_ir;
 
   llvm_unreachable("should handle all dump modes");
 }

toolchain/parser/parser.cpp

@@ -433,8 +433,6 @@ auto Parser::Parse() -> void {
   // Traces state_stack_. This runs even in opt because it's low overhead.
   PrettyStackTraceParseState pretty_stack(this);
 
-  CARBON_VLOG() << "*** Parser::Parse Begin ***\n";
-
   PushState(ParserState::DeclarationLoop());
   while (!state_stack_.empty()) {
     switch (state_stack_.back().state) {
@@ -447,8 +445,6 @@ auto Parser::Parse() -> void {
   }
 
   AddLeafNode(ParseNodeKind::FileEnd(), *position_);
-
-  CARBON_VLOG() << "*** Parser::Parse End ***\n";
 }
 
 auto Parser::HandleBraceExpressionState() -> void {

toolchain/semantics/semantics_parse_tree_handler.cpp

@@ -63,7 +63,6 @@ auto SemanticsParseTreeHandler::Build() -> void {
   PrettyStackTraceNodeStack pretty_node_stack(this);
   PrettyStackTraceNodeBlockStack pretty_node_block_stack(this);
 
-  CARBON_VLOG() << "*** SemanticsParseTreeHandler::Build Begin ***\n";
   // Add a block for the ParseTree.
   node_block_stack_.push_back(semantics_->AddNodeBlock());
 
@@ -85,7 +84,6 @@ auto SemanticsParseTreeHandler::Build() -> void {
         CARBON_CHECK(it == range.end())
             << "FileEnd should always be last, found "
             << parse_tree_->node_kind(*it);
-        CARBON_VLOG() << "*** SemanticsParseTreeHandler::Build End ***\n";
         return;
       }
       case ParseNodeKind::InfixOperator(): {