Exception — Elixir v1.18.3 (original) (raw)

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

Types

The kind handled by formatting functions

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.

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 kind() :: :error | non_error_kind()

The kind handled by formatting functions

@type non_error_kind() :: :exit | :throw | {:EXIT, pid()}

@type stacktrace() :: [stacktrace_entry()]

@type t() :: %{ :struct => module(), :exception => true, optional(atom()) => any() }

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.

@callback exception(term()) :: t()

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/2callback, 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/oris wrapped in a tuple with blame metadata.

This function returns either {:ok, definition, clauses} or :error. Where definition is :def, :defp, :defmacro or :defmacrop.

Normalizes and formats throw/errors/exits and stacktraces.

It relies on format_banner/3 and format_stacktrace/1to generate the final format.

If kind is {:EXIT, pid}, it does not generate a stacktrace, as such exits are retrieved as messages without stacktraces.

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"

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)
""

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)
""

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.

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.