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type_expr.rs
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README.md

DreamChecker

DreamChecker is a robust whole-program static analysis and type checking engine for DreamMaker, the scripting language of the BYOND game engine.

Running DreamChecker

DreamChecker can be obtained with cargo build -p dreamchecker or from the releases page.

DreamChecker should be run from within the DM project directory. It will automatically detect the .dme file, parse it, and issue diagnostics. DreamChecker will exit with a non-zero status code if it discovers any diagnostics, making it suitable for use in continuous integration environments.

Diagnostics

In addition to the simple inline diagnostics discovered by the parsing suite, DreamCheckers's whole-program analysis can find problems such as:

  • Unknown set setting names.
  • Undefined types on unused variables.
  • Keyword arguments being passed to procs which do not accept them.
  • Calling procs with non-keyword arguments following keyword arguments.
  • Proc overrides which are missing keyword arguments that their parents are called with.
  • Declaring vars with /list in unusual positions, e.g. var/atom/list/movable/L.
  • Use of src in global /procs where it is guaranteed to be null.
  • Calling the parent proc ..() when no such parent exists.
  • Accesses like L[1].foo and foo().bar wherein . acts like : instead.
    • List accesses perform lookups according to the type appended to /list, e.g. with var/list/obj/L, the type of L[1] will be /obj and a lookup of L[1].name will not generate a warning.
    • Proc calls will obey the return type annotation if present.

Extensions

DreamChecker also adds additional typing features to the language through a series of extensions, described below. Because DreamMaker does not recognize these extensions, it is recommended that you use the preprocessor flag SPACEMAN_DMM to determine whether they should be enabled:

#ifdef SPACEMAN_DMM
	#define RETURN_TYPE(X) set SpacemanDMM_return_type = X
	#define SHOULD_CALL_PARENT(X) set SpacemanDMM_should_call_parent = X
#else
	#define RETURN_TYPE(X)
	#define SHOULD_CALL_PARENT(X)
#endif

Return type

Use set SpacemanDMM_return_type = expression to set a return type expression for a proc. The return type can take the forms:

  • /typepath - a raw typepath. The return type of the proc is the type named.
  • param - a typepath given as a parameter, for procs which return an instance of the passed-in type.
  • param.type - the static type of a passed-in parameter, for procs which return their input or otherwise another value of the same type.
  • param[_].type - the static type of a passed-in parameter, with one level of /list stripped, for procs which select one item from a list. The [_] may be repeated to strip more levels of /list.

Should call parent

Use set SpacemanDMM_should_call_parent = 1 to enable a diagnostic on children of the proc it is set on which do not contain any ..() parent calls. This can help with finding situations where a signal or other important handling in the parent proc is being skipped. Child procs may set this setting to 0 instead to override the check.