View Source Exception behaviour (Elixir v1.18.0-dev)
Functions for dealing with throw/catch/exit and exceptions.
This module also defines the behaviour required by custom
exceptions. To define your own, see defexception/1.
Formatting functions
Several functions in this module help format exceptions.
Some of these functions expect the stacktrace as argument.
The stacktrace is typically available inside catch and
rescue by using the __STACKTRACE__/0 variable.
Do not rely on the particular format returned by the functions in this module. They may be changed in future releases in order to better suit Elixir's tool chain. In other words, by using the functions in this module it is guaranteed you will format exceptions as in the current Elixir version being used.
Summary
Callbacks
Called from Exception.blame/3 to augment the exception struct.
Receives the arguments given to raise/2 and returns the exception struct.
Receives the exception struct and must return its message.
Functions
Attaches information to exceptions for extra debugging.
Blames the invocation of the given module, function and arguments.
Normalizes and formats throw/errors/exits and stacktraces.
Normalizes and formats any throw/error/exit.
Formats an exit. It returns a string.
Receives an anonymous function and arity and formats it as shown in stacktraces. The arity may also be a list of arguments.
Formats the given file and line as shown in stacktraces.
Formats the given file, line, and column as shown in stacktraces.
Receives a module, fun and arity and formats it as shown in stacktraces. The arity may also be a list of arguments.
Formats the stacktrace.
Receives a stacktrace entry and formats it into a string.
Gets the message for an exception.
Normalizes an exception, converting Erlang exceptions to Elixir exceptions.
Types
@type arity_or_args() :: non_neg_integer() | list()
@type kind() :: :error | non_error_kind()
The kind handled by formatting functions
@type location() :: keyword()
@type non_error_kind() :: :exit | :throw | {:EXIT, pid()}
@type stacktrace() :: [stacktrace_entry()]
@type stacktrace_entry() :: {module(), atom(), arity_or_args(), location()} | {(... -> any()), arity_or_args(), location()}
The exception type
Callbacks
@callback blame(t(), stacktrace()) :: {t(), stacktrace()}
Called from Exception.blame/3 to augment the exception struct.
Can be used to collect additional information about the exception or do some additional expensive computation.
Receives the arguments given to raise/2 and returns the exception struct.
The default implementation accepts either a set of keyword arguments that is merged into the struct or a string to be used as the exception's message.
Receives the exception struct and must return its message.
Many exceptions have a message field which by default is accessed by this function. However, if an exception does not have a message field, this function must be explicitly implemented.
Functions
@spec blame(:error, any(), stacktrace()) :: {t(), stacktrace()}
@spec blame(non_error_kind(), payload, stacktrace()) :: {payload, stacktrace()} when payload: var
Attaches information to exceptions for extra debugging.
This operation is potentially expensive, as it reads data from the file system, parses beam files, evaluates code and so on.
If the exception module implements the optional blame/2
callback, it will be invoked to perform the computation.
@spec blame_mfa(module(), function :: atom(), args :: [term()]) :: {:ok, :def | :defp | :defmacro | :defmacrop, [{args :: [term()], guards :: [term()]}]} | :error
Blames the invocation of the given module, function and arguments.
This function will retrieve the available clauses from bytecode
and evaluate them against the given arguments. The clauses are
returned as a list of {args, guards} pairs where each argument
and each top-level condition in a guard separated by and/or
is wrapped in a tuple with blame metadata.
This function returns either {:ok, definition, clauses} or :error.
Where definition is :def, :defp, :defmacro or :defmacrop.
@spec format(kind(), any(), stacktrace()) :: String.t()
Normalizes and formats throw/errors/exits and stacktraces.
It relies on format_banner/3 and format_stacktrace/1
to generate the final format.
If kind is {:EXIT, pid}, it does not generate a stacktrace,
as such exits are retrieved as messages without stacktraces.
@spec format_banner(kind(), any(), stacktrace()) :: String.t()
Normalizes and formats any throw/error/exit.
The message is formatted and displayed in the same format as used by Elixir's CLI.
The third argument is the stacktrace which is used to enrich a normalized error with more information. It is only used when the kind is an error.
Formats an exit. It returns a string.
Often there are errors/exceptions inside exits. Exits are often wrapped by the caller and provide stacktraces too. This function formats exits in a way to nicely show the exit reason, caller and stacktrace.
Receives an anonymous function and arity and formats it as shown in stacktraces. The arity may also be a list of arguments.
Examples
Exception.format_fa(fn -> nil end, 1)
#=> "#Function<...>/1"@spec format_file_line(String.t() | nil, non_neg_integer() | nil, String.t()) :: String.t()
Formats the given file and line as shown in stacktraces.
If any of the values are nil, they are omitted.
Examples
iex> Exception.format_file_line("foo", 1)
"foo:1:"
iex> Exception.format_file_line("foo", nil)
"foo:"
iex> Exception.format_file_line(nil, nil)
""@spec format_file_line_column( String.t() | nil, non_neg_integer() | nil, non_neg_integer() | nil, String.t() ) :: String.t()
Formats the given file, line, and column as shown in stacktraces.
If any of the values are nil, they are omitted.
Examples
iex> Exception.format_file_line_column("foo", 1, 2)
"foo:1:2:"
iex> Exception.format_file_line_column("foo", 1, nil)
"foo:1:"
iex> Exception.format_file_line_column("foo", nil, nil)
"foo:"
iex> Exception.format_file_line_column("foo", nil, 2)
"foo:"
iex> Exception.format_file_line_column(nil, nil, nil)
""@spec format_mfa(module(), atom(), arity_or_args()) :: String.t()
Receives a module, fun and arity and formats it as shown in stacktraces. The arity may also be a list of arguments.
Examples
iex> Exception.format_mfa(Foo, :bar, 1)
"Foo.bar/1"
iex> Exception.format_mfa(Foo, :bar, [])
"Foo.bar()"
iex> Exception.format_mfa(nil, :bar, [])
"nil.bar()"Anonymous functions are reported as -func/arity-anonfn-count-, where func is the name of the enclosing function. Convert to "anonymous fn in func/arity"
@spec format_stacktrace(stacktrace() | nil) :: String.t()
Formats the stacktrace.
A stacktrace must be given as an argument. If not, the stacktrace
is retrieved from Process.info/2.
@spec format_stacktrace_entry(stacktrace_entry()) :: String.t()
Receives a stacktrace entry and formats it into a string.
Gets the message for an exception.
@spec normalize(:error, any(), stacktrace()) :: t()
@spec normalize(non_error_kind(), payload, stacktrace()) :: payload when payload: var
Normalizes an exception, converting Erlang exceptions to Elixir exceptions.
It takes the kind spilled by catch as an argument and
normalizes only :error, returning the untouched payload
for others.
The third argument is the stacktrace which is used to enrich a normalized error with more information. It is only used when the kind is an error.