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A common idiom in CMake-based build systems is to have custom commands that generate files not listed explicitly as outputs so that these files do not have to be newer than the inputs. The file modification times of such "byproducts" are updated only when their content changes. Then other build rules can depend on the byproducts explicitly so that their dependents rebuild when the content of the original byproducts really does change. This "undeclared byproduct" approach is necessary for Makefile, VS, and Xcode build tools because if a byproduct were listed as an output of a rule then the rule would always rerun when the input is newer than the byproduct but the byproduct may never be updated. Ninja solves this problem by offering a 'restat' feature to check whether an output was really modified after running a rule and tracking the fact that it is up to date separately from its timestamp. However, Ninja also stats all dependencies up front and will only restat files that are listed as outputs of rules with the 'restat' option enabled. Therefore an undeclared byproduct that does not exist at the start of the build will be considered missing and the build will fail even if other dependencies would cause the byproduct to be available before its dependents build. CMake works around this limitation by adding 'phony' build rules for custom command dependencies in the build tree that do not have any explicit specification of what produces them. This is not optimal because it prevents Ninja from reporting an error when an input to a rule really is missing. A better approach is to allow projects to explicitly specify the byproducts of their custom commands so that no phony rules are needed for them. In order to work with the non-Ninja generators, the byproducts must be known separately from the outputs. Add a new "BYPRODUCTS" option to the add_custom_command and add_custom_target commands to specify byproducts explicitly. Teach the Ninja generator to specify byproducts as outputs of the custom commands. In the case of POST_BUILD, PRE_LINK, and PRE_BUILD events on targets that link, the byproducts must be specified as outputs of the link rule that runs the commands. Activate 'restat' for such rules so that Ninja knows it needs to check the byproducts, but not for link rules that have no byproducts.
107 lines
3.6 KiB
C++
107 lines
3.6 KiB
C++
/*============================================================================
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CMake - Cross Platform Makefile Generator
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Copyright 2000-2009 Kitware, Inc., Insight Software Consortium
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Distributed under the OSI-approved BSD License (the "License");
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see accompanying file Copyright.txt for details.
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This software is distributed WITHOUT ANY WARRANTY; without even the
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implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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See the License for more information.
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============================================================================*/
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#ifndef cmCustomCommand_h
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#define cmCustomCommand_h
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#include "cmStandardIncludes.h"
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#include "cmListFileCache.h"
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class cmMakefile;
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/** \class cmCustomCommand
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* \brief A class to encapsulate a custom command
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*
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* cmCustomCommand encapsulates the properties of a custom command
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*/
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class cmCustomCommand
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{
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public:
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/** Default and copy constructors for STL containers. */
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cmCustomCommand();
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cmCustomCommand(const cmCustomCommand& r);
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cmCustomCommand& operator=(cmCustomCommand const& r);
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/** Main constructor specifies all information for the command. */
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cmCustomCommand(cmMakefile const* mf,
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const std::vector<std::string>& outputs,
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const std::vector<std::string>& byproducts,
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const std::vector<std::string>& depends,
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const cmCustomCommandLines& commandLines,
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const char* comment,
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const char* workingDirectory);
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~cmCustomCommand();
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/** Get the output file produced by the command. */
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const std::vector<std::string>& GetOutputs() const;
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/** Get the extra files produced by the command. */
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const std::vector<std::string>& GetByproducts() const;
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/** Get the vector that holds the list of dependencies. */
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const std::vector<std::string>& GetDepends() const;
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/** Get the working directory. */
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std::string const& GetWorkingDirectory() const
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{ return this->WorkingDirectory; }
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/** Get the list of command lines. */
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const cmCustomCommandLines& GetCommandLines() const;
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/** Get the comment string for the command. */
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const char* GetComment() const;
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/** Append to the list of command lines. */
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void AppendCommands(const cmCustomCommandLines& commandLines);
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/** Append to the list of dependencies. */
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void AppendDepends(const std::vector<std::string>& depends);
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/** Set/Get whether old-style escaping should be used. */
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bool GetEscapeOldStyle() const;
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void SetEscapeOldStyle(bool b);
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/** Set/Get whether the build tool can replace variables in
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arguments to the command. */
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bool GetEscapeAllowMakeVars() const;
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void SetEscapeAllowMakeVars(bool b);
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/** Backtrace of the command that created this custom command. */
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cmListFileBacktrace const& GetBacktrace() const;
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typedef std::pair<std::string, std::string> ImplicitDependsPair;
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class ImplicitDependsList: public std::vector<ImplicitDependsPair> {};
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void SetImplicitDepends(ImplicitDependsList const&);
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void AppendImplicitDepends(ImplicitDependsList const&);
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ImplicitDependsList const& GetImplicitDepends() const;
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/** Set/Get whether this custom command should be given access to the
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real console (if possible). */
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bool GetUsesTerminal() const;
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void SetUsesTerminal(bool b);
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private:
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std::vector<std::string> Outputs;
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std::vector<std::string> Byproducts;
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std::vector<std::string> Depends;
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cmCustomCommandLines CommandLines;
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bool HaveComment;
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std::string Comment;
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std::string WorkingDirectory;
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bool EscapeAllowMakeVars;
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bool EscapeOldStyle;
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cmListFileBacktrace Backtrace;
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ImplicitDependsList ImplicitDepends;
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bool UsesTerminal;
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};
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#endif
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