1. The bodies of all clauses in all user and library modules. This steps collects, but does not scan multifile predicates to avoid duplicate work.
2. All multi-file predicates collected.
3. All goals registered with initialization/1

Options processed:

undefined(+Action)

Action defines what happens if the analysis finds a definitely undefined predicate. One of ignore or error (default is ignore).

autoload(+Boolean)

Try to autoload code while walking. This is enabled by default to obtain as much as possible information about goals and find references from autoloaded libraries.

clauses(+ListOfClauseReferences)

Only process the given clauses. Can be used to find clauses quickly using source(false) and then process only interesting clauses with source information.

module(+Module)

Only process the given module

module_class(+ModuleClassList)

Limit processing to modules of the given classes. See module_property/2 for details on module classes. Default is to scan the classes user and library.

infer_meta_predicates(+BooleanOrAll)

Use infer_meta_predicate/2 on predicates with clauses that call known meta-predicates. The analysis is restarted until a fixed point is reached. If true (default), analysis is only restarted if the inferred meta-predicate contains a callable argument. If all, it will be restarted until no more new meta-predicates can be found.

walk_meta_predicates(Boolean)

When false (default true), do not analyse the arguments of meta predicates. Standard Prolog control structures are always analysed.

trace_reference(Callable)

Print all calls to goals that subsume Callable. Goals are represented as Module:Callable (i.e., they are always qualified). See also subsumes_term/2.

trace_condition(:Cond)

Additional filter condition applied after trace_reference. Called as call(Cond, Callee, Context), where Context is a dict containing the following keys:

caller:Context

Qualified term representing the caller or the atom '<initialization>'.

module:Context

Module being processed

clause:Context

If we are processing a normal clause, the clause reference to this clause.

initialization:Context

If we are processing an initialization/1 directive, a term File:Line representing the location of the declaration.

on_edge(:OnEdge)

If a reference to trace_reference is found, call call(OnEdge, Callee, Caller, Location), where Location is a dict containing a subset of the keys clause, file, character_count, line_count and line_position. If full position information is available all keys are present. If the clause layout is unknown the only the clause, file and line_count are available and the line is the start line of the clause. For a dynamic clause, only the clause is present. If the position is associated to a directive, the clause is missing. If nothing is known the Location is an empty dict.

on_trace(:OnTrace)

As on_edge, but location is not translated and is one of these:

• clause_term_position(+ClauseRef, +TermPos)
• clause(+ClauseRef)
• file_term_position(+Path, +TermPos)
• file(+File, +Line, -1, _)
• a variable (unknown)

Caller is the qualified head of the calling clause or the atom '<initialization>'.

source(+Boolean)

If false (default true), to not try to obtain detailed source information for printed messages.

verbose(+Boolean)

If true (default false), report derived meta-predicates and iterations.

@compat OnTrace was called using Caller-Location in older versions.