Use the new diagnostics for wgsl the parser

Keep the `ParserImpl::error()` format identical to the old error style for now.
Use the explicit `ParserImpl::diagnostics()` method for the error message tests, updating the tests to match the new, improved output.

Bug: tint:282
Change-Id: Ia7e1237170f0f5203a8cfa256322df29e90e2791
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/31481
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: dan sinclair <dsinclair@chromium.org>

src/reader/wgsl/parser_impl.cc

@@ -132,27 +132,15 @@ ParserImpl::~ParserImpl() {
 }
 
 void ParserImpl::set_error(const Token& t, const std::string& err) {
-  auto prefix = std::to_string(t.source().range.begin.line) + ":" +
-                std::to_string(t.source().range.begin.column) + ": ";
-
-  if (t.IsReservedKeyword()) {
-    error_ = prefix + "reserved token (" + t.to_str() + ") found";
-    return;
-  }
-  if (t.IsError()) {
-    error_ = prefix + t.to_str();
-    return;
-  }
-
-  if (err.size() != 0) {
-    error_ = prefix + err;
-  } else {
-    error_ = prefix + "invalid token (" + t.to_name() + ") encountered";
-  }
+  diag::Diagnostic diagnostic;
+  diagnostic.severity = diag::Severity::Error;
+  diagnostic.message = err;
+  diagnostic.source = t.source();
+  diags_.add(std::move(diagnostic));
 }
 
 void ParserImpl::set_error(const Token& t) {
-  set_error(t, "");
+  set_error(t, "invalid token (" + t.to_name() + ") encountered");
 }
 
 Token ParserImpl::next() {

src/reader/wgsl/parser_impl.h

@@ -45,6 +45,8 @@
 #include "src/ast/variable.h"
 #include "src/ast/variable_decoration.h"
 #include "src/context.h"
+#include "src/diagnostic/diagnostic.h"
+#include "src/diagnostic/formatter.h"
 #include "src/reader/wgsl/token.h"
 
 namespace tint {
@@ -99,9 +101,15 @@ class ParserImpl {
   bool Parse();
 
   /// @returns true if an error was encountered.
-  bool has_error() const { return error_.size() > 0; }
+  bool has_error() const { return diags_.contains_errors(); }
+
   /// @returns the parser error string
-  const std::string& error() const { return error_; }
+  std::string error() const {
+    return diag::Formatter::create(false, false, false)->format(diags_);
+  }
+
+  /// @returns the diagnostic messages
+  const diag::List& diagnostics() const { return diags_; }
 
   /// @returns the module. The module in the parser will be reset after this.
   ast::Module module() { return std::move(module_); }
@@ -418,7 +426,7 @@ class ParserImpl {
       uint32_t depth);
 
   Context& ctx_;
-  std::string error_;
+  diag::List diags_;
   std::unique_ptr<Lexer> lexer_;
   std::deque<Token> token_queue_;
   std::unordered_map<std::string, ast::type::Type*> registered_constructs_;