tools/gn/input_conversion.cc

// Copyright (c) 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "tools/gn/input_conversion.h"

#include "base/strings/string_split.h"
#include "base/strings/string_util.h"
#include "tools/gn/build_settings.h"
#include "tools/gn/err.h"
#include "tools/gn/input_file.h"
#include "tools/gn/label.h"
#include "tools/gn/parse_tree.h"
#include "tools/gn/parser.h"
#include "tools/gn/scheduler.h"
#include "tools/gn/scope.h"
#include "tools/gn/settings.h"
#include "tools/gn/tokenizer.h"
#include "tools/gn/value.h"

namespace {

enum ValueOrScope {
  PARSE_VALUE,  // Treat the input as an expression.
  PARSE_SCOPE,  // Treat the input as code and return the resulting scope.
};

// Sets the origin of the value and any nested values with the given node.
Value ParseValueOrScope(const Settings* settings,
                        const std::string& input,
                        ValueOrScope what,
                        const ParseNode* origin,
                        Err* err) {
  // The memory for these will be kept around by the input file manager
  // so the origin parse nodes for the values will be preserved.
  InputFile* input_file;
  std::vector<Token>* tokens;
  scoped_ptr<ParseNode>* parse_root_ptr;
  g_scheduler->input_file_manager()->AddDynamicInput(
      SourceFile(), &input_file, &tokens, &parse_root_ptr);

  input_file->SetContents(input);
  if (origin) {
    // This description will be the blame for any error messages caused by
    // script parsing or if a value is blamed. It will say
    // "Error at <...>:line:char" so here we try to make a string for <...>
    // that reads well in this context.
    input_file->set_friendly_name(
        "dynamically parsed input that " +
        origin->GetRange().begin().Describe(true) +
        " loaded ");
  } else {
    input_file->set_friendly_name("dynamic input");
  }

  *tokens = Tokenizer::Tokenize(input_file, err);
  if (err->has_error())
    return Value();

  // Parse the file according to what we're looking for.
  if (what == PARSE_VALUE)
    *parse_root_ptr = Parser::ParseValue(*tokens, err);
  else
    *parse_root_ptr = Parser::Parse(*tokens, err);  // Will return a Block.
  if (err->has_error())
    return Value();
  ParseNode* parse_root = parse_root_ptr->get();  // For nicer syntax below.

  // It's valid for the result to be a null pointer, this just means that the
  // script returned nothing.
  if (!parse_root)
    return Value();

  scoped_ptr<Scope> scope(new Scope(settings));
  Value result = parse_root->Execute(scope.get(), err);
  if (err->has_error())
    return Value();

  // When we want the result as a scope, the result is actually the scope
  // we made, rather than the result of running the block (which will be empty).
  if (what == PARSE_SCOPE) {
    DCHECK(result.type() == Value::NONE);
    result = Value(origin, scope.Pass());
  }
  return result;
}

Value ParseList(const std::string& input, const ParseNode* origin, Err* err) {
  Value ret(origin, Value::LIST);
  std::vector<std::string> as_lines;
  base::SplitString(input, '\n', &as_lines);

  // Trim one empty line from the end since the last line might end in a
  // newline. If the user wants more trimming, they'll specify "trim" in the
  // input conversion options.
  if (!as_lines.empty() && as_lines[as_lines.size() - 1].empty())
    as_lines.resize(as_lines.size() - 1);

  ret.list_value().reserve(as_lines.size());
  for (const auto& line : as_lines)
    ret.list_value().push_back(Value(origin, line));
  return ret;
}

// Backend for ConvertInputToValue, this takes the extracted string for the
// input conversion so we can recursively call ourselves to handle the optional
// "trim" prefix. This original value is also kept for the purposes of throwing
// errors.
Value DoConvertInputToValue(const Settings* settings,
                            const std::string& input,
                            const ParseNode* origin,
                            const Value& original_input_conversion,
                            const std::string& input_conversion,
                            Err* err) {
  if (input_conversion.empty())
    return Value();  // Empty string means discard the result.

  const char kTrimPrefix[] = "trim ";
  if (StartsWithASCII(input_conversion, kTrimPrefix, true)) {
    std::string trimmed;
    base::TrimWhitespaceASCII(input, base::TRIM_ALL, &trimmed);

    // Remove "trim" prefix from the input conversion and re-run.
    return DoConvertInputToValue(
        settings, trimmed, origin, original_input_conversion,
        input_conversion.substr(arraysize(kTrimPrefix) - 1), err);
  }

  if (input_conversion == "value")
    return ParseValueOrScope(settings, input, PARSE_VALUE, origin, err);
  if (input_conversion == "string")
    return Value(origin, input);
  if (input_conversion == "list lines")
    return ParseList(input, origin, err);
  if (input_conversion == "scope")
    return ParseValueOrScope(settings, input, PARSE_SCOPE, origin, err);

  *err = Err(original_input_conversion, "Not a valid input_conversion.",
             "Have you considered a career in retail?");
  return Value();
}

}  // namespace

extern const char kInputConversion_Help[] =
    "input_conversion: Specifies how to transform input to a variable.\n"
    "\n"
    "  input_conversion is an argument to read_file and exec_script that\n"
    "  specifies how the result of the read operation should be converted\n"
    "  into a variable.\n"
    "\n"
    "  \"\" (the default)\n"
    "      Discard the result and return None.\n"
    "\n"
    "  \"list lines\"\n"
    "      Return the file contents as a list, with a string for each line.\n"
    "      The newlines will not be present in the result. The last line may\n"
    "      or may not end in a newline.\n"
    "\n"
    "      After splitting, each individual line will be trimmed of\n"
    "      whitespace on both ends.\n"
    "\n"
    "  \"scope\"\n"
    "      Execute the block as GN code and return a scope with the\n"
    "      resulting values in it. If the input was:\n"
    "        a = [ \"hello.cc\", \"world.cc\" ]\n"
    "        b = 26\n"
    "      and you read the result into a variable named \"val\", then you\n"
    "      could access contents the \".\" operator on \"val\":\n"
    "        sources = val.a\n"
    "        some_count = val.b\n"
    "\n"
    "  \"string\"\n"
    "      Return the file contents into a single string.\n"
    "\n"
    "  \"value\"\n"
    "      Parse the input as if it was a literal rvalue in a buildfile.\n"
    "      Examples of typical program output using this mode:\n"
    "        [ \"foo\", \"bar\" ]     (result will be a list)\n"
    "      or\n"
    "        \"foo bar\"            (result will be a string)\n"
    "      or\n"
    "        5                    (result will be an integer)\n"
    "\n"
    "      Note that if the input is empty, the result will be a null value\n"
    "      which will produce an error if assigned to a variable.\n"
    "\n"
    "  \"trim ...\"\n"
    "      Prefixing any of the other transformations with the word \"trim\"\n"
    "      will result in whitespace being trimmed from the beginning and end\n"
    "      of the result before processing.\n"
    "\n"
    "      Examples: \"trim string\" or \"trim list lines\"\n"
    "\n"
    "      Note that \"trim value\" is useless because the value parser skips\n"
    "      whitespace anyway.\n";

Value ConvertInputToValue(const Settings* settings,
                          const std::string& input,
                          const ParseNode* origin,
                          const Value& input_conversion_value,
                          Err* err) {
  if (input_conversion_value.type() == Value::NONE)
    return Value();  // Allow null inputs to mean discard the result.
  if (!input_conversion_value.VerifyTypeIs(Value::STRING, err))
    return Value();
  return DoConvertInputToValue(settings, input, origin, input_conversion_value,
                               input_conversion_value.string_value(), err);
}