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/sourceDependencies:directives (List module and header unit dependencies)

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This command-line option scans source files and their #include statements to generate a JSON file that lists module export and imports. This information can be used by a build system to determine the build order of modules and header units.

This option differs from /sourceDependencies in the following ways:

  • The compiler doesn't produce compiled output. No compiled code, modules, or header units are produced. Instead, the files are scanned for module directives.
  • The JSON format is different from what /sourceDependencies produces. The /sourceDependencies option is intended to be used with other build tools, such as CMake.
  • The output JSON file doesn't list imported modules and imported header units (.ifc files) because this option does a scan of the project files, not a compilation. So there are no built modules or header units to list.
  • Only directly imported modules or header units are listed. It doesn't list the dependencies of the imported modules or header units themselves.
  • Header file dependencies aren't listed. That is, #include <file> or #include "file" dependencies aren't listed.
  • /sourceDependencies:directives is meant to be used before .ifc files are built.
  • /sourceDependencies causes the compiler to report all of the files, such as #includes, .pch files, .ifc files, and so on, that were used for a particular translation unit, whereas /sourceDependencies:directives [file1] scans the specified source file and reports all import and export statements. /sourceDependencies can be used with /sourceDependencies:directives.

Syntax

/sourceDependencies:directives-
/sourceDependencies:directives filename
/sourceDependencies:directives directory

Arguments

-
If the single dash is provided, then the compiler will emit the source dependencies JSON to stdout, or to where compiler output is redirected.

filename
The compiler writes the source dependency output to the specified filename, which may include a relative or absolute path. The file is created if it doesn't exist.

directory
If the argument is a directory, the compiler generates source dependency files in the specified directory. The directory must exist, or the argument is treated as a filename. The output file name is based on the full name of the input file, with an appended .json extension. For example, if the file provided to the compiler is main.cpp, the generated output filename is main.cpp.json.

Remarks

/sourceDependencies:directives is available starting in Visual Studio 2019 version 16.10.

When you specify the /MP (Build with multiple processes) compiler option, we recommend that you use /sourceDependencies:directives with a directory argument. This option makes the compiler output a separate *.module.json file for each source file. If you provide a single filename argument, two instances of the compiler may attempt to open the output file simultaneously and cause an error. Use of /MP with /sourceDependencies:directives- to send output to stdout could cause interleaved results.

When a non-fatal compiler error occurs, the dependency information still gets written to the output file.

All file paths appear as absolute paths in the output.

This switch can be used with /translateInclude.

Examples

Given the following sample code:

//main.cpp:
#include <vector>

import m;
import std.core;

import <utility>;

import "t.h";

int main() {}

This following command line:

cl /std:c++latest /translateInclude /sourceDependencies:directives output.json main.cpp

produces a JSON file output.json similar to:

{
   "Version":"1.1",
   "Data":{
      "Source":"C:\\a\\b\\main.cpp",
      "ProvidedModule":"",
      "ImportedModules":[
         "m",
         "std.core"
      ],
      "ImportedHeaderUnits":[
         "C:\\...\\utility",
         "C:\\a\\b\\t.h"
      ]
   }
}

For brevity, the previous example uses ... to abbreviate the reported paths. The report contains the absolute paths. The paths reported depend on where the compiler finds the dependencies. If the results are unexpected, you might want to check your project's include path settings.

ProvidedModule lists exported module or module partition names.

No .ifc files are listed in the output because they weren't built. Unlike /sourceDependencies, the compiler doesn't produce compiled output when /sourceDependencies:directives is specified, so no compiled modules or header units are produced.

To set this compiler option in Visual Studio

You normally shouldn't set this option yourself in the Visual Studio development environment. It's set by the build system.

See also

/translateInclude
C++ header-units.json reference
MSVC compiler options
MSVC compiler command-line syntax
/scanDependencies (List module dependencies in standard form)
/sourceDependencies (List all source-level dependencies)