Add initial prototype for the GN meta-buildsystem.

tools/gn/input_conversion.cc

Index: tools/gn/input_conversion.cc
diff --git a/tools/gn/input_conversion.cc b/tools/gn/input_conversion.cc
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+++ b/tools/gn/input_conversion.cc
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+// 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 "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/scope.h"
+#include "tools/gn/settings.h"
+#include "tools/gn/tokenizer.h"
+#include "tools/gn/value.h"
+
+namespace {
+
+// Returns the "first bit" of some script output for writing to error messages.
+std::string GetExampleOfBadInput(const std::string& input) {
+  std::string result(input);
+
+  // Maybe the result starts with a blank line or something, which we don't
+  // want.
+  TrimWhitespaceASCII(result, TRIM_ALL, &result);
+
+  // Now take the first line, or the first set of chars, whichever is shorter.
+  bool trimmed = false;
+  size_t newline_offset = result.find('\n');
+  if (newline_offset != std::string::npos) {
+    trimmed = true;
+    result.resize(newline_offset);
+  }
+  TrimWhitespaceASCII(result, TRIM_ALL, &result);
+
+  const int kMaxSize = 50;
+  if (result.size() > kMaxSize) {
+    trimmed = true;
+    result.resize(kMaxSize);
+  }
+
+  if (trimmed)
+    result.append("...");
+  return result;
+}
+
+// When parsing the result as a value, we may get various types of errors.
+// This creates an error message for this case with an optional nested error
+// message to reference. If there is no nested err, pass Err().
+//
+// This code also takes care to rewrite the original error which will reference
+// the temporary InputFile which won't exist when the error is propogated
+// out to a higher level.
+Err MakeParseErr(const std::string& input,
+                 const ParseNode* origin,
+                 const Err& nested) {
+  std::string help_text =
+      "When parsing a result as a \"value\" it should look like a list:\n"
+      "  [ \"a\", \"b\", 5 ]\n"
+      "or a single literal:\n"
+      "  \"my result\"\n"
+      "but instead I got this, which I find very confusing:\n";
+  help_text.append(input);
+  if (nested.has_error())
+    help_text.append("\nThe exact error was:");
+
+  Err result(origin, "Script result wasn't a valid value.", help_text);
+  if (nested.has_error()) {
+    result.AppendSubErr(Err(LocationRange(), nested.message(),
+                            nested.help_text()));
+  }
+  return result;
+}
+
+// Sets the origin of the value and any nested values with the given node.
+void RecursivelySetOrigin(Value* value, const ParseNode* origin) {
+  value->set_origin(origin);
+  if (value->type() == Value::LIST) {
+    std::vector<Value>& list_value = value->list_value();
+    for (size_t i = 0; i < list_value.size(); i++)
+      RecursivelySetOrigin(&list_value[i], origin);
+  }
+}
+
+Value ParseString(const std::string& input,
+                  const ParseNode* origin,
+                  Err* err) {
+  SourceFile empty_source_for_most_vexing_parse;
+  InputFile input_file(empty_source_for_most_vexing_parse);
+  input_file.SetContents(input);
+
+  std::vector<Token> tokens = Tokenizer::Tokenize(&input_file, err);
+  if (err->has_error()) {
+    *err = MakeParseErr(input, origin, *err);
+    return Value();
+  }
+
+  scoped_ptr<ParseNode> expression = Parser::ParseExpression(tokens, err);
+  if (err->has_error()) {
+    *err = MakeParseErr(input, origin, *err);
+    return Value();
+  }
+
+  // It's valid for the result to be a null pointer, this just means that the
+  // script returned nothing.
+  if (!expression)
+    return Value();
+
+  // The result should either be a list or a literal, anything else is
+  // invalid.
+  if (!expression->AsList() && !expression->AsLiteral()) {
+    *err = MakeParseErr(input, origin, Err());
+    return Value();
+  }
+
+  BuildSettings build_settings;
+  Label empty_label;
+  Toolchain toolchain(empty_label);
+  Settings settings(&build_settings, &toolchain, std::string());
+  Scope scope(&settings);
+
+  Err nested_err;
+  Value result = expression->Execute(&scope, &nested_err);
+  if (nested_err.has_error()) {
+    *err = MakeParseErr(input, origin, nested_err);
+    return Value();
+  }
+
+  // The returned value will have references to the temporary parse nodes we
+  // made on the stack. If the values are used in an error message in the
+  // future, this will crash. Reset the origin of all values to be our
+  // containing origin.
+  RecursivelySetOrigin(&result, origin);
+  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 empty lines from the end.
+  // Do we want to make this configurable?
+  while (!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 (size_t i = 0; i < as_lines.size(); i++)
+    ret.list_value().push_back(Value(origin, as_lines[i]));
+  return ret;
+}
+
+}  // namespace
+
+/*
+input_conversion: Specifies how to transform input to a variable.
+
+  input_conversion is an argument to read_file and exec_script that specifies
+  how the result of the read operation should be converted into a variable.
+
+  "list lines":
+      Return the file contents as a list, with a string for each line. The
+      newlines will not be present in the result. Empty newlines will be
+      trimmed from the trailing end of the returned list.
+
+  "value":
+      Parse the input as if it was a literal rvalue in a buildfile.
+      Examples of typical program output using this mode:
+        [ "foo", "bar" ]     (result will be a list)
+      or
+        "foo bar"            (result will be a string)
+      or
+        5                    (result will be an integer)
+
+      Note that if the input is empty, the result will be a null value which
+      will produce an error if assigned to a variable.
+
+  "string":
+      Return the file contents into a single string.
+*/
+
+Value ConvertInputToValue(const std::string& input,
+                          const ParseNode* origin,
+                          const Value& input_conversion_value,
+                          Err* err) {
+  if (!input_conversion_value.VerifyTypeIs(Value::STRING, err))
+    return Value();
+  const std::string& input_conversion = input_conversion_value.string_value();
+
+  if (input_conversion == "value")
+    return ParseString(input, origin, err);
+  if (input_conversion == "string")
+    return Value(origin, input);
+  if (input_conversion == "list lines")
+    return ParseList(input, origin, err);
+
+  *err = Err(input_conversion_value, "Not a valid read file mode.",
+             "Have you considered a career in retail?");
+  return Value();
+}