Add initial prototype for the GN meta-buildsystem.

tools/gn/scope.h

Index: tools/gn/scope.h
diff --git a/tools/gn/scope.h b/tools/gn/scope.h
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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.
+
+#ifndef TOOLS_GN_SCOPE_H_
+#define TOOLS_GN_SCOPE_H_
+
+#include <map>
+#include <set>
+
+#include "base/basictypes.h"
+#include "base/containers/hash_tables.h"
+#include "base/memory/scoped_ptr.h"
+#include "tools/gn/err.h"
+#include "tools/gn/pattern.h"
+#include "tools/gn/value.h"
+
+class FunctionCallNode;
+class ImportManager;
+class ParseNode;
+class Settings;
+class TargetManager;
+
+// Scope for the script execution.
+//
+// Scopes are nested. Writing goes into the toplevel scope, reading checks
+// values resursively down the stack until a match is found or there are no
+// more containing scopes.
+//
+// A containing scope can be const or non-const. The const containing scope is
+// used primarily to refer to the master build config which is shared across
+// many invocations. A const containing scope, however, prevents us from
+// marking variables "used" which prevents us from issuing errors on unused
+// variables. So you should use a non-const containing scope whenever possible.
+class Scope {
+ public:
+  typedef std::vector<std::pair<base::StringPiece, Value> > KeyValueVector;
+
+  // Allows code to provide values for built-in variables. This class will
+  // automatically register itself on construction and deregister itself on
+  // destruction.
+  class ProgrammaticProvider {
+   public:
+    ProgrammaticProvider(Scope* scope) : scope_(scope) {
+      scope_->AddProvider(this);
+    }
+    ~ProgrammaticProvider() {
+      scope_->RemoveProvider(this);
+    }
+
+    // Returns a non-null value if the given value can be programmatically
+    // generated, or NULL if there is none.
+    virtual const Value* GetProgrammaticValue(
+        const base::StringPiece& ident) = 0;
+
+   protected:
+    Scope* scope_;
+  };
+
+  // Creates an empty toplevel scope.
+  Scope(const Settings* settings);
+
+  // Creates a dependent scope.
+  Scope(Scope* parent);
+  Scope(const Scope* parent);
+
+  ~Scope();
+
+  const Settings* settings() const { return settings_; }
+
+  // See the const_/mutable_containing_ var declaraions below. Yes, it's a
+  // bit weird that we can have a const pointer to the "mutable" one.
+  Scope* mutable_containing() { return mutable_containing_; }
+  const Scope* mutable_containing() const { return mutable_containing_; }
+  const Scope* const_containing() const { return const_containing_; }
+  const Scope* containing() const {
+    return mutable_containing_ ? mutable_containing_ : const_containing_;
+  }
+
+  // Returns NULL if there's no such value.
+  //
+  // counts_as_used should be set if the variable is being read in a way that
+  // should count for unused variable checking.
+  const Value* GetValue(const base::StringPiece& ident,
+                        bool counts_as_used);
+  const Value* GetValue(const base::StringPiece& ident) const;
+
+  // Same as GetValue, but if the value exists in a parent scope, we'll copy
+  // it to the current scope. If the return value is non-null, the value is
+  // guaranteed to be set in the current scope. Generatlly this will be used
+  // if the calling code is planning on modifying the value in-place.
+  //
+  // Since this is used when doing read-modifies, we never count this access
+  // as reading the variable, since we assume it will be written to.
+  Value* GetValueForcedToCurrentScope(const base::StringPiece& ident,
+                                      const ParseNode* set_node);
+
+  // The set_node indicates the statement that caused the set, for displaying
+  // errors later. Returns a pointer to the value in the current scope (a copy
+  // is made for storage).
+  Value* SetValue(const base::StringPiece& ident,
+                  const Value& v,
+                  const ParseNode* set_node);
+
+  // Templates associated with this scope. A template can only be set once, so
+  // AddTemplate will fail and return NULL if a rule with that name already
+  // exists. GetTemplate returns NULL if the rule doesn't exist, and it will
+  // check all containing scoped rescursively.
+  bool AddTemplate(const std::string& name, const FunctionCallNode* decl);
+  const FunctionCallNode* GetTemplate(const std::string& name) const;
+
+  // Marks the given identifier as (un)used in the current scope.
+  void MarkUsed(const base::StringPiece& ident);
+  void MarkUnused(const base::StringPiece& ident);
+
+  // Checks to see if the scope has a var set that hasn't been used. This is
+  // called before replacing the var with a different one. It does not check
+  // containing scopes.
+  //
+  // If the identifier is present but hasnn't been used, return true.
+  bool IsSetButUnused(const base::StringPiece& ident) const;
+
+  // Checks the scope to see if any values were set but not used, and fills in
+  // the error and returns false if they were.
+  bool CheckForUnusedVars(Err* err) const;
+
+  // Returns all values set in the current scope, without going to the parent
+  // scopes.
+  void GetCurrentScopeValues(KeyValueVector* output) const;
+
+  // Copies this scope's values into the destination. Values from the
+  // containing scope(s) (normally shadowed into the current one) will not be
+  // copied, neither will the reference to the containing scope (this is why
+  // it's "non-recursive").
+  //
+  // It is an error to merge a variable into a scope that already has something
+  // with that name in scope (meaning in that scope or in any of its containing
+  // scopes). If this happens, the error will be set and the function will
+  // return false.
+  //
+  // This is used in different contexts. When generating the error, the given
+  // parse node will be blamed, and the given desc will be used to describe
+  // the operation that doesn't support doing this. For example, desc_for_err
+  // would be "import" when doing an import, and the error string would say
+  // something like "The import contains...".
+  bool NonRecursiveMergeTo(Scope* dest,
+                           const ParseNode* node_for_err,
+                           const char* desc_for_err,
+                           Err* err) const;
+
+  // Makes an empty scope with the given name. Returns NULL if the name is
+  // already set.
+  Scope* MakeTargetDefaults(const std::string& target_type);
+
+  // Gets the scope associated with the given target name, or null if it hasn't
+  // been set.
+  const Scope* GetTargetDefaults(const std::string& target_type) const;
+
+  // Filter to apply when the sources variable is assigned. May return NULL.
+  const PatternList* GetSourcesAssignmentFilter() const;
+  void set_sources_assignment_filter(
+      scoped_ptr<PatternList> f) {
+    sources_assignment_filter_ = f.Pass();
+  }
+
+  // Indicates if we're currently processing the build configuration file.
+  // This is true when processing the config file for any toolchain. See also
+  // *ProcessingDefaultBuildConfig() below.
+  //
+  // To set or clear the flag, it must currently be in the opposite state in
+  // the current scope. Note that querying the state of the flag recursively
+  // checks all containing scopes until it reaches the top or finds the flag
+  // set.
+  void SetProcessingBuildConfig();
+  void ClearProcessingBuildConfig();
+  bool IsProcessingBuildConfig() const;
+
+  // Indicates we're currently processing the default toolchain's build
+  // configuration file.
+  void SetProcessingDefaultBuildConfig();
+  void ClearProcessingDefaultBuildConfig();
+  bool IsProcessingDefaultBuildConfig() const;
+
+  // Indicates if we're currently processing an import file.
+  //
+  // See SetProcessingBaseConfig for how flags work.
+  void SetProcessingImport();
+  void ClearProcessingImport();
+  bool IsProcessingImport() const;
+
+  // Properties are opaque pointers that code can use to set state on a Scope
+  // that it can retrieve later.
+  //
+  // The key should be a pointer to some use-case-specific object (to avoid
+  // collisions, otherwise it doesn't matter). Memory management is up to the
+  // setter. Setting the value to NULL will delete the property.
+  //
+  // Getting a property recursively searches all scopes, and the optional
+  // |found_on_scope| variable will be filled with the actual scope containing
+  // the key (if the pointer is non-NULL).
+  void SetProperty(const void* key, void* value);
+  void* GetProperty(const void* key, const Scope** found_on_scope) const;
+
+ private:
+  friend class ProgrammaticProvider;
+
+  struct Record {
+    Record() : used(false) {}
+    Record(const Value& v) : used(false), value(v) {}
+
+    bool used;  // Set to true when the variable is used.
+    Value value;
+  };
+
+  void AddProvider(ProgrammaticProvider* p);
+  void RemoveProvider(ProgrammaticProvider* p);
+
+  // Scopes can have no containing scope (both null), a mutable containing
+  // scope, or a const containing scope. The reason is that when we're doing
+  // a new target, we want to refer to the base_config scope which will be read
+  // by multiple threads at the same time, so we REALLY want it to be const.
+  // When you jsut do a nested {}, however, we sometimes want to be able to
+  // change things (especially marking unused vars).
+  const Scope* const_containing_;
+  Scope* mutable_containing_;
+
+  const Settings* settings_;
+
+  // Bits set for different modes. See the flag definitions in the .cc file
+  // for more.
+  unsigned mode_flags_;
+
+  typedef base::hash_map<base::StringPiece, Record> RecordMap;
+  RecordMap values_;
+
+  // Owning pointers. Note that this can't use string pieces since the names
+  // are constructed from Values which might be deallocated before this goes
+  // out of scope.
+  typedef base::hash_map<std::string, Scope*> NamedScopeMap;
+  NamedScopeMap target_defaults_;
+
+  // Null indicates not set and that we should fallback to the containing
+  // scope's filter.
+  scoped_ptr<PatternList> sources_assignment_filter_;
+
+  // Non-owning pointers, the function calls are owned by the input file which
+  // should be kept around by the input file manager.
+  typedef std::map<std::string, const FunctionCallNode*> TemplateMap;
+  TemplateMap templates_;
+
+  typedef std::map<const void*, void*> PropertyMap;
+  PropertyMap properties_;
+
+  typedef std::set<ProgrammaticProvider*> ProviderSet;
+  ProviderSet programmatic_providers_;
+
+  DISALLOW_COPY_AND_ASSIGN(Scope);
+};
+
+#endif  // TOOLS_GN_SCOPE_H_