clang-uml/docs/common_options.md

Common diagram generation options

• Overall configuration file structure
• Translation unit glob patterns
• Custom directives
• Adding debug information in the generated diagrams
• Resolving include path and compiler flags issues
  • Use '--query-driver' command line option
  • Manually add and remove compile flags from the compilation database
  • Using 'CMAKE_CXX_IMPLICIT_INCLUDE_DIRECTORIES'

Overall configuration file structure

By default, clang-uml will look for file .clang-uml in the projects directory and read all diagrams definitions from it. The file must be specified in YAML and it's overall structure is as follows:

# common options for all diagrams
...
diagrams:
  first_diagram_name:
    type: class|sequence|package|include
    # diagram specific options
    ...
  second_diagram_name:
    type: class|sequence|package|include
    # diagram specific options
    ...
  ...

The top level common options are inherited by specific diagrams, if the option is applicable to them and they themselves do not override this option.

For detailed reference of all configuration options see here.

Effective configuration, including default values can be printed out in YAML format using the following option:

clang-uml --dump-config

Diagram titles

Each type of diagram can have a title property, which will be generated in the diagram using directives specific to a given diagram generator, for instance:

diagrams:
  diagram1:
    type: class
    title: Some explanatory diagram title

Translation unit glob patterns

One of the key options of the diagram configuration is the list of translation units, which should be parsed to get all necessary information for a diagram.

The syntax is simple and based on glob patterns, which can be added to the configuration file as follows:

   glob:
     - src/dir1/*.cc
     - src/dir3/*.cc

The glob patterns only need to match the translation units, which are also in the compile_commands.json file, i.e. any files that match the glob patterns but are not in compile_commands.json will be ignored. In case the glob pattern set does not match any translation units an error will be printed on the standard output.

For small projects, the glob property can be omitted, which will result in clang-uml parsing all translation units from compile_commands.json for the diagram. However for large projects, constraining the number of translation units for each diagram to absolute minimum will significantly decrease the diagram generation times.

Custom directives

In case it's necessary to add some custom PlantUML or MermaidJS declarations before or after the generated diagram content, it can be achieved simply using the plantuml or mermaid configuration properties, for instance for PlantUML:

    plantuml:
      before:
        - left to right direction
      after:
        - note left of {{ alias("ns1::ns2::MyClass") }} This is my class. 

or for MermaidJS:

    mermaid:
      before:
        - direction LR
      after:
        - note for {{ alias("ns1::ns2::MyClass") }} "This is my class." 

These directive are useful for instance for adding notes to elements in the diagrams or customizing diagram layout or style.

Please note that when referring to diagram elements in the PlantUML directives, they must be added using Jinja templates alias command as in the example above.

More options can be found in the official docs for each respective generator:

• PlantUML
• MermaidJS

Adding debug information in the generated diagrams

Sometimes it is useful for debugging issues with the diagrams to have information on the exact source location, from which given declaration or call expression was derived. By adding option:

debug_mode: true

the generated PlantUML diagram will contain comments before each line containing the source location of the specific diagram element.

Resolving include path and compiler flags issues

Due to the fact, that your project can be compiled with different compilers and toolchains, the system paths and compilation flags detected by the Clang version linked to your clang-uml installation might differ from the ones actually used to compile your project.

This is often an issue on macOS, when clang-uml uses Homebrew version of LLVM and your project was built using system Apple Clang

Typically, this results in error messages on the console during diagram generation, such as:

... fatal: 'stddef.h' file not found

or

... warning: implicit conversion from 'int' to 'float' changes value from 2147483647 to 2147483648 [-Wimplicit-const-int-float-conversion]

These errors can be overcome, by ensuring that the Clang parser has the correct include paths to analyse your code base on the given platform. clang-uml provides several mechanisms to resolve this issue:

Use '--query-driver' command line option

This option is not available on Windows.

Providing this option on the clang-uml command line will result in clang-uml executing the specified compiler with the following command, e.g.:

/usr/bin/c++ -E -v -x c /dev/null 2>&1

and extracting from the output the target and system include paths, which are then injected to each entry of the compilation database. For instance, on my system, when generating diagrams for an embedded project and providing arm-none-eabi-gcc as driver:

clang-uml --query-driver arm-none-eabi-gcc

the following options are appended to each command line after argv[0] of the command:

--target=arm-none-eabi -isystem /usr/lib/gcc/arm-none-eabi/10.3.1/include -isystem /usr/lib/gcc/arm-none-eabi/10.3.1/include-fixed -isystem /usr/lib/gcc/arm-none-eabi/10.3.1/../../../arm-none-eabi/include

If you want to include the system headers reported by the compiler specified already as argv[0] in your compile_commands.json, you can simply invoke clang-uml as:

clang-uml --query-driver .

however please make sure that the compile_commands.json contains a command, which is safe to execute.

Manually add and remove compile flags from the compilation database

If the system paths extracted from the compiler are not sufficient to resolve include paths issues, it is possible to manually adjust the compilation flags by providing add_compile_flags and remove_compile_flags in the configuration file, or providing --add-compile-flag and --remove-compile-flag on the clang-uml command line.

For instance:

add_compile_flags:
  - -I/opt/my_toolchain/include
remove_compile_flags:
  - -I/usr/include

These options can be also passed on the command line, for instance:

clang-uml --add-compile-flag -I/opt/my_toolchain/include \
          --remove-compile-flag -I/usr/include ...

Using 'CMAKE_CXX_IMPLICIT_INCLUDE_DIRECTORIES'

Yet another option, for CMake based projects, is to use the following CMake option:

set(CMAKE_CXX_STANDARD_INCLUDE_DIRECTORIES ${CMAKE_CXX_IMPLICIT_INCLUDE_DIRECTORIES})