Regression test system for Emacs font-lock keywords
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faceup - Markup language for faces and font-lock regression testing

Author: Anders Lindgren
Version: 0.0.5

Emacs is capable of highlighting buffers based on language-specific font-lock rules. This package makes it possible to perform regression test for packages that provide font-lock rules.

The underlying idea is to convert text with highlights ("faces") into a plain text representation using the Faceup markup language. This language is semi-human readable, for example:

«k:this» is a keyword

By comparing the current highlight with a highlight performed with stable versions of a package, it's possible to automatically find problems that otherwise would have been hard to spot.

This package is designed to be used in conjunction with Ert, the standard Emacs regression test system.

The Faceup markup language is a generic markup language, regression testing is merely one way to use it.

Regression test examples

This section describes the two typical ways regression testing with this package is performed.

Full source file highlighting

The most straight-forward way to perform regression testing is to collect a number of representative source files. From each source file, say alpha.mylang, you can use M-x faceup-write-file RET to generate a Faceup file named alpha.mylang.faceup, this file use the Faceup markup language to represent the text with highlights and is used as a reference in future tests.

An Ert test case can be defined as follows:

   (require 'faceup)

   (defvar mylang-font-lock-test-dir (faceup-this-file-directory))

   (defun mylang-font-lock-test-apps (file)
     "Test that the mylang FILE is fontifies as the .faceup file describes."
     (faceup-test-font-lock-file 'mylang-mode
                                 (concat mylang-font-lock-test-dir file)))
   (faceup-defexplainer mylang-font-lock-test-apps)

   (ert-deftest mylang-font-lock-file-test ()
     (should (mylang-font-lock-test-apps "apps/FirstApp/alpha.mylang"))
     ;; ... Add more test files here ...

To execute the tests, run something like M-x ert RET t RET.

Source snippets

To test smaller snippets of code, you can use the faceup-test-font-lock-string. It takes a major mode and a string written using the Faceup markup language. The functions strips away the Faceup markup, inserts the plain text into a temporary buffer, highlights it, converts the result back into the Faceup markup language, and finally compares the result with the original Faceup string.

For example:

   (defun mylang-font-lock-test (faceup)
     (faceup-test-font-lock-string 'mylang-mode faceup))
   (faceup-defexplainer mylang-font-lock-test)

   (ert-deftest mylang-font-lock-test-simple ()
     "Simple MyLang font-lock tests."
     (should (mylang-font-lock-test "«k:this» is a keyword"))
     (should (mylang-font-lock-test "«k:function» «f:myfunc» («v:var»)")))

Executing the tests

Once the tests have been defined, you can use M-x ert RET t RET to execute them. Hopefully, you will be given the "all clear". However, if there is a problem, you will be presented with something like:

F mylang-font-lock-file-test
       (mylang-font-lock-test-apps "apps/FirstApp/alpha.mylang"))
      (mylang-font-lock-test-apps "apps/FirstApp/alpha.mylang")
      :value nil :explanation
      ((on-line 2

You should read this that on line 2, the old font-lock rules highlighted this inside but_this_is_not_a_keyword (which is clearly wrong), whereas the new doesn't. Of course, if this is the desired result (for example, the result of a recent change) you can simply regenerate the .faceup file and store it as the reference file for the future.

The Faceup markup language

The Faceup markup language is designed to be human-readable and minimalistic.

The two special characters « and » marks the start and end of a range of a face.

Compact format for special faces

The compact format «<LETTER>:text» is used for a number of common faces. For example, «U:abc» means that the text abc is underlined.

See faceup-face-short-alist for the known faces and the corresponding letter.

Full format

The format «:<NAME OF FACE>:text» is used use to encode other faces.

For example «:my-special-face:abc» meanst that abc has the face my-special-face.

Anonymous faces

An "anonymous face" is when the face property contains a property list (plist) on the form (:key value). This is represented using a variant of the full format: «:(:key value):text».

For example, «:(:background "red"):abc» represent the text abc with a red background.

Multiple properties

In case a text contains more than one face property, they are represented using nested sections.

For example:

  • «B:abc«U:def»» represent the text abcdef that is both bold and underlined.
  • «W:abc«U:def»ghi» represent the text abcdefghi where the entire text is in warning face and def is underlined.

In case two faces partially overlap, the ranges will be split when represented in Faceup. For example:

  • «B:abc«U:def»»«U:ghi» represent the text abcdefghi where abcdef is bold and defghi is underlined.

Escaping start and end markers

Any occurrence of the start or end markers in the original text will be escaped using the start marker in the Faceup representation. In other words, the sequences «« and «» represent a start and end marker, respectively.

Other properties

In addition to representing the face property (or, more correctly, the value of faceup-default-property) other properties can be encoded. The variable faceup-properties contains a list of properties to track. If a property behaves like the face property, it is encoded as described above, with the addition of the property name placed in parentheses, for example: «(my-face)U:abd».

The variable faceup-face-like-properties contains a list of properties considered face-like.

Properties that are not considered face-like are always encoded using the full format and the don't nest. For example: «(my-fibonacci-property):(1 1 2 3 5 8):abd».

Examples of properties that could be tracked are:

  • font-lock-face -- an alias to face when font-lock-mode is enabled.
  • syntax-table -- used by a custom syntax-propertize to override the default syntax table.
  • help-echo -- provides tooltip text displayed when the mouse is held over a text.

Reference section

Faceup commands and functions

M-x faceup-write-file RET - generate a Faceup file based on the current buffer.

M-x faceup-view-file RET - view the current buffer converted to Faceup.

faceup-markup-{string,buffer} - convert text with properties to the Faceup markup language.

faceup-render-view-buffer - convert buffer with Faceup markup to a buffer with real text properties and display it.

faceup-render-string - return string with real text properties from a string with Faceup markup.

faceup-render-to-{buffer,string} - convert buffer with Faceup markup to a buffer/string with real text properties.

faceup-clean-{buffer,string} - remove Faceup markup from buffer or string.

Regression test support

The following functions can be used as Ert test functions, or can be used to implement new Ert test functions.

faceup-test-equal - Test function, work like Ert:s equal, but more ergonomically when reporting multi-line string errors. Concretely, it breaks down multi-line strings into lines and reports which line number the error occurred on and the content of that line.

faceup-test-font-lock-buffer - Test that a buffer is highlighted according to a reference Faceup text, for a specific major mode.

faceup-test-font-lock-string - Test that a text with Faceup markup is refontified to match the original Faceup markup.

faceup-test-font-lock-file - Test that a file is highlighted according to a reference .faceup file.

faceup-defexplainer - Macro, define an explainer function and set the ert-explainer property on the original function, for functions based on the above test functions.

faceup-this-file-directory - Macro, the directory of the current file.

Real-world examples

The following are examples of real-world package that use faceup to test their font-lock keywords.

Other Font Lock Tools

This package is part of a suite of font-lock tools. The other tools in the suite are:

Font Lock Studio

Interactive debugger for font-lock keywords (Emacs syntax highlighting rules).

Font Lock Studio lets you single-step Font Lock keywords -- matchers, highlights, and anchored rules, so that you can see what happens when a buffer is fontified. You can set breakpoints on or inside rules and run until one has been hit. When inside a rule, matches are visualized using a palette of background colors. The explainer can describe a rule in plain-text English. Tight integration with Edebug allows you to step into Lisp expressions that are part of the Font Lock keywords.

Font Lock Profiler

A profiler for font-lock keywords. This package measures time and counts the number of times each part of a font-lock keyword is used. For matchers, it counts the total number and the number of successful matches.

The result is presented in table that can be sorted by count or time. The table can be expanded to include each part of the font-lock keyword.

In addition, this package can generate a log of all font-lock events. This can be used to verify font-lock implementations, concretely, this is used for back-to-back tests of the real font-lock engine and Font Lock Studio, an interactive debugger for font-lock keywords.

Highlight Refontification

Minor mode that visualizes how font-lock refontifies a buffer. This is useful when developing or debugging font-lock keywords, especially for keywords that span multiple lines.

The background of the buffer is painted in a rainbow of colors, where each band in the rainbow represent a region of the buffer that has been refontified. When the buffer is modified, the rainbow is updated.

Face Explorer

Library and tools for faces and text properties.

This library is useful for packages that convert syntax highlighted buffers to other formats. The functions can be used to determine how a face or a face text property looks, in terms of primitive face attributes (e.g. foreground and background colors). Two sets of functions are provided, one for existing frames and one for fictitious displays, like 8 color tty.

In addition, the following tools are provided:

  • face-explorer-list-faces -- list all available faces. Like list-faces-display but with information on how a face is defined. In addition, a sample for the selected frame and for a fictitious display is shown.
  • face-explorer-describe-face -- Print detailed information on how a face is defined, and list all underlying definitions.
  • face-explorer-describe-face-prop -- Describe the face text property at the point in terms of primitive face attributes. Also show how it would look on a fictitious display.
  • face-explorer-list-display-features -- Show which features a display supports. Most graphical displays support all, or most, features. However, many tty:s don't support, for example, strike-through. Using specially constructed faces, the resulting buffer will render differently in different displays, e.g. a graphical frame and a tty connected using emacsclient -nw.
  • face-explorer-list-face-prop-examples -- Show a buffer with an assortment of face text properties. A sample text is shown in four variants: Native, a manually maintained reference vector, the result of face-explorer-face-prop-attributes and face-explorer-face-prop-attributes-for-fictitious-display. Any package that convert a buffer to another format (like HTML, ANSI, or LaTeX) could use this buffer to ensure that everything work as intended.
  • face-explorer-list-overlay-examples -- Show a buffer with a number of examples of overlays, some are mixed with face text properties. Any package that convert a buffer to another format (like HTML, ANSI, or LaTeX) could use this buffer to ensure that everything work as intended.
  • face-explorer-tooltip-mode -- Minor mode that shows tooltips containing text properties and overlays at the mouse pointer.
  • face-explorer-simulate-display-mode -- Minor mode for make a buffer look like it would on a fictitious display. Using this you can, for example, see how a theme would look in using dark or light background, a 8 color tty, or on a grayscale graphical monitor.

Font Lock Regression Suite

A collection of example source files for a large number of programming languages, with ERT tests to ensure that syntax highlighting does not accidentally change.

For each source file, font-lock reference files are provided for various Emacs versions. The reference files contains a plain-text representation of source file with syntax highlighting, using the format "faceup".

Of course, the collection source file can be used for other kinds of testing, not limited to font-lock regression testing.

Converted from faceup.el by el2markdown.