[Lldb-commits] [lldb] [LLDB] Add Lexer (with tests) for DIL (Data Inspection Language). (PR #123521)

[via lldb-commits]

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+//===-- DILLexer.cpp ------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// This implements the recursive descent parser for the Data Inspection
+// Language (DIL), and its helper functions, which will eventually underlie the
+// 'frame variable' command. The language that this parser recognizes is
+// described in lldb/docs/dil-expr-lang.ebnf
+//
+//===----------------------------------------------------------------------===//
+
+#include "lldb/ValueObject/DILLexer.h"
+#include "lldb/Utility/Status.h"
+#include "llvm/ADT/StringSwitch.h"
+
+namespace lldb_private::dil {
+
+llvm::StringRef Token::GetTokenName(Kind kind) {
+  switch (kind) {
+  case Kind::coloncolon:
+    return "coloncolon";
+  case Kind::eof:
+    return "eof";
+  case Kind::identifier:
+    return "identifier";
+  case Kind::l_paren:
+    return "l_paren";
+  case Kind::r_paren:
+    return "r_paren";
+  case Kind::unknown:
+    return "unknown";
+  }
+}
+
+static bool IsLetter(char c) {
+  return ('a' <= c && c <= 'z') || ('A' <= c && c <= 'Z');
+}
+
+static bool IsDigit(char c) { return '0' <= c && c <= '9'; }
+
+// A word starts with a letter, underscore, or dollar sign, followed by
+// letters ('a'..'z','A'..'Z'), digits ('0'..'9'), and/or  underscores.
+static std::optional<llvm::StringRef> IsWord(llvm::StringRef expr,
+                                             llvm::StringRef &remainder) {
+  llvm::StringRef::iterator cur_pos = expr.end() - remainder.size();
+  llvm::StringRef::iterator start = cur_pos;
+  bool dollar_start = false;
+
+  // Must not start with a digit.
+  if (cur_pos == expr.end() || IsDigit(*cur_pos))
+    return std::nullopt;
+
+  // First character *may* be a '$', for a register name or convenience
+  // variable.
+  if (*cur_pos == '$') {
+    dollar_start = true;
+    ++cur_pos;
+  }
+
+  // Contains only letters, digits or underscores
+  for (; cur_pos != expr.end(); ++cur_pos) {
+    char c = *cur_pos;
+    if (!IsLetter(c) && !IsDigit(c) && c != '_')
+      break;
+  }
+
+  // If first char is '$', make sure there's at least one mare char, or it's
+  // invalid.
+  if (dollar_start && (cur_pos - start <= 1)) {
+    cur_pos = start;
+    return std::nullopt;
+  }
+
+  if (cur_pos == start)
+    return std::nullopt;
+
+  llvm::StringRef word = expr.substr(start - expr.begin(), cur_pos - start);
+  if (remainder.consume_front(word))
+    return word;
+
+  return std::nullopt;
+}
+
+llvm::Expected<DILLexer> DILLexer::Create(llvm::StringRef expr) {
+  std::vector<Token> tokens;
+  llvm::StringRef remainder = expr;
+  do {
+    if (llvm::Expected<Token> t = Lex(expr, remainder)) {
+      tokens.push_back(std::move(*t));
+    } else {
+      return t.takeError();
+    }
+  } while (tokens.back().GetKind() != Token::eof);
+  return DILLexer(expr, std::move(tokens));
+}
+
+llvm::Expected<Token> DILLexer::Lex(llvm::StringRef expr,
+                                    llvm::StringRef &remainder) {
+  // Skip over whitespace (spaces).
+  remainder = remainder.ltrim();
+  llvm::StringRef::iterator cur_pos = expr.end() - remainder.size();
----------------
cmtice wrote:

"Both stringrefs are pointers to the same underlying string" -- I did not know that.  SO...there's a string (const char *) in memory, that both StringRefs point to, and updating the StringRefs never updates the underlying memory contents?  Hm...it would be nice if there was documentation somewhere that made this clear (the doxygen stuff does NOT).  Thanks for the explanation & clarification.

https://github.com/llvm/llvm-project/pull/123521