clj-commons.format.exceptions — org.clj-commons/pretty 3.1.0

Format and output exceptions in a pretty (structured, formatted) way.

*app-frame-names* clj

Set of strings or regular expressions defining the application's namespaces, which allows such namespaces to be highlighted in exception output.

*default-frame-filter* clj

(*default-frame-filter* frame)

Default stack frame filter used when printing REPL exceptions, driven by *default-frame-rules*.

*default-frame-rules* clj

The set of rules that forms the basis for *default-frame-filter*, as a vector of vectors.

Each rule is a vector of three values:

• A function that extracts the value from the stack frame map (typically, this is a keyword such as :package or :name). The value is converted to a string.
• A string or regexp used for matching. Strings must match exactly.
• A resulting frame visibility (:hide, :omit, :terminate, or :show).

The default rules:

• omit everything in clojure.lang, java.lang.reflect, and the function clojure.core/apply
• hide everything in sun.reflect
• terminate at speclj.*, clojure.main/main*, clojure.main/repl/read-eval-print, or nrepl.middleware.interruptible-eval

*fonts* clj

Current set of fonts used in exception formatting. This can be overridden to change colors, or bound to nil to disable fonts. Defaults are defined by default-fonts.

*print-length* clj

The number of elements of collections to pretty-print; defaults to 10.

*print-level* clj

The depth to which to pretty-printed nested collections; defaults to 5.

*traditional* clj

If bound to true, then exceptions will be formatted the traditional way - the same as Java exceptions with the deepest stack frame first. By default, the stack trace is inverted, so that the deepest stack frames come last, mimicking chronological order.

analyze-exception clj

(analyze-exception e options)

Converts an exception into a seq of maps representing nested exceptions. The order reflects exception nesting; first exception is the most recently thrown, last is the deepest, or root, exception ... the initial exception thrown in a chain of nested exceptions.

The options map is as defined by format-exception.

Each exception map contains:

Key	Type	Description
:class-name	String	Name of Java class for the exception
:message	String	Value of the exception's message property (possibly nil)
:properties	String	Map of properties to (optionally) present in the exception report
:stack-trace	Vector	Stack trace element maps (as per expand-stack-trace), or nil; only present in the root exception

The :properties map does not include any properties that are assignable to type Throwable.

The first property that is assignable to type Throwable (not necessarily the rootCause property) will be used as the nested exception (for the next map in the sequence).

default-fonts clj

A default map of [[compose]] font defs for different elements in the formatted exception report.

demangle clj

(demangle s)

De-mangle a Java name back to a Clojure name by converting mangled sequences, such as "QMARK" back into simple characters.

exception-dispatch clj multimethod

The pretty print dispatch function used when formatting exception output (specifically, when printing the properties of an exception). Normally, this is the same as the simple-dispatch (in clojure.pprint) but can be extended for specific cases:

(import com.stuartsierra.component.SystemMap)

(defmethod exception-dispatch SystemMap [system-map] (print "#<SystemMap>"))

This ensures that the SystemMap record, wherever it appears in the exception output, is represented as the string #<SystemMap>; normally it would print as a deeply nested tree of maps.

This same approach can be adapted to any class or type whose structure is problematic for presenting in the exception output, whether for size and complexity reasons, or due to security concerns.

expand-stack-trace clj

(expand-stack-trace exception)

Extracts the stack trace for an exception and returns a seq of stack frame maps; a wrapper around transform-stack-trace.

filter-stack-trace-maps clj

(filter-stack-trace-maps elements)

(filter-stack-trace-maps elements options)

Filters the stack trace maps (from transform-stack-trace, removing unnecessary frames and applying a filter and optional frame-limit (:filter and :frame-limit options).

The default frame filter is *default-frame-filter*.

Returns the elements, filtered, and (in some cases) with an additional :omitted key (true for frames that should be omitted). This includes discarding elements that the filter indicates to :hide, and coalescing frames the filter indicates to :omit.

format-exception clj

(format-exception exception)

(format-exception exception options)

Formats an exception, returning a single large string.

By default, includes the stack trace, with no frame limit.

The options map may have the following keys:

Key	Description
:filter	The stack frame filter, which defaults to [[default-stack-frame-filter]]
:properties	If true (the default) then properties of exceptions will be output
:frame-limit	If non-nil, the number of stack frames to keep when outputting the stack trace of the deepest exception

Output may be traditional or modern, as controlled by *traditional*. Traditional is the typical output order for Java: the stack of exceptions comes first (outermost to innermost) followed by the stack trace of the innermost exception, with the frames in order from deepest to most shallow.

Modern output is more readable; the stack trace comes first and is reversed: shallowest frame to most deep. Then the exception stack is output, from the root exception to the outermost exception. The modern output order is more readable, as it puts the most useful information together at the bottom, so that it is not necessary to scroll back to see, for example, where the exception occurred.

The default is modern.

The stack frame filter is passed the map detailing each stack frame in the stack trace, and must return one of the following values:

Value	Description
:show	The normal state; display the stack frame
:hide	Prevents the frame from being displayed, as if it never existed
:omit	Replaces the frame with a "..." placeholder
:terminate	Hides the frame AND all later frames

Multiple consecutive :omits will be collapsed to a single line; use :omit for "uninteresting" stack frames.

The default filter is *default-frame-filter*. An explicit filter of nil will display all stack frames.

Repeating lines are collapsed to a single line, with a repeat count. Typically, this is the result of an endless loop that terminates with a StackOverflowException.

When set, the frame limit is the number of stack frames to display; if non-nil, then some outermost stack frames may be omitted. It may be set to 0 to omit the stack trace entirely (but still display the exception stack). The frame limit is applied after the frame filter (which may hide or omit frames) and after repeating stack frames have been identified and coalesced ... :frame-limit is really the number of output lines to present.

Properties of exceptions will be output using Clojure's pretty-printer, but using this namespace's versions of *print-length* and *print-level*, which default to 10 and 2, respectively.

The *fonts* var contains a map from output element names (as :exception or :clojure-frame) to a font def used with [[compose]]; this allows easy customization of the output.

format-exception* clj

(format-exception* exception-stack options)

Contains the main logic for format-exception, which simply expands the exception (via analyze-exception) before invoking this function.

format-stack-frame clj

(format-stack-frame {:keys [file line names repeats] :as frame})

Transforms an expanded stack frame (see transform-stack-trace) into a formatted stack frame:

Key	Type	Description
:name	composed string	Formatted version of the stack frame :name (or :names)
:name-width	Integer	Visual width of the name
:file	String	Location of source (or nil)
:line	String	Location of source (or nil)
:repeats	Integer	Number of times the frame repeats (or nil)

Formatting is based on whether the frame is omitted, and whether it is a Clojure or Java frame.

parse-exception clj

(parse-exception exception-text options)

Given a chunk of text from an exception report (as with .printStackTrace), attempts to piece together the same information provided by analyze-exception. The result is ready to pass to [[write-exception*]].

This code does not attempt to recreate properties associated with the exceptions; in most exception's cases, this is not necessarily written to the output. For clojure.lang.ExceptionInfo, it is hard to distinguish the message text from the printed exception map.

The options are used when processing the stack trace and may include the :filter and :frame-limit keys.

Returns a sequence of exception maps; the final map will include the :stack-trace key (a vector of stack trace element maps). The exception maps are ordered outermost to innermost (that final map is the root exception).

This should be considered experimental code; there are many cases where it may not work properly.

It will work quite poorly with exceptions whose message incorporates a nested exception's .printStackTrace output. This happens too often with JDBC exceptions, for example.

print-exception clj

(print-exception exception)

(print-exception exception options)

Formats an exception via format-exception, then prints it to *out*. Accepts the same options as format-exception.

transform-stack-trace clj

(transform-stack-trace elements)

Transforms a seq of StackTraceElement objects into a seq of stack frame maps:

Key	Type	Description
:file	String	Source file name, or nil if not known
:line	Integer	Line number as integer, or nil
:class	String	Fully qualified Java class name
:package	String	Java package name, or nil for root package
:simple-class	String	Simple name of Java class, without the package prefix
:method	String	Java method name
:is-clojure?	Boolean	If true, this represents a Clojure function call, rather than a Java method invocation
:id	String	An id that can be used to identify repeating stack frames; consists of the fully qualified method name (for Java frames) or fully qualified Clojure name (for Clojure frames) appended with the line number.
:name	String	Fully qualified Clojure name (demangled from the Java class name), or the empty string for non-Clojure stack frames
:names	seq of String	Clojure name split at slashes (empty for non-Clojure stack frames)