Codebraid Preview
Codebraid Preview provides a Markdown preview for
Pandoc documents within VS
Code. Most Markdown previews don't support
all of Pandoc's extensions to Markdown syntax. Codebraid Preview supports
100% of Pandoc features—because the preview is generated by Pandoc itself!
There is also full bidirectional scroll sync and document export.
Codebraid Preview provides optional support for executing code blocks and
inline code to embed their output in the preview and in exported documents.
Code execution is performed by
Codebraid using Jupyter kernels or its
own built-in code execution system. When code is running, the preview still
updates whenever the document is modified, displaying all code output that is
currently available. The preview always remains live.
Features
HTML preview of Pandoc documents. Open the preview by running the "Open
Codebraid Preview" command (Ctrl+Shift+P, then type command). Or, for
Markdown documents, just click on the "Codebraid Preview" button in the
status bar (bottom right). When changes are detected, the preview
automatically refreshes.
Full bidirectional scroll sync. This requires processing the document
as commonmark_x, which is CommonMark plus
Pandoc extensions.
commonmark_x has
most of the features
in Pandoc's Markdown and continues to gain new features. See the note about
commonmark_x below for more details.
Math support with KaTeX. Surround LaTeX math with
single dollar signs $ for inline math or double dollar signs $$ for
block math, following standard Pandoc conventions.
Adjustable scroll sync directions. Once a preview window is open, click
on the "Scroll" button in the status bar (bottom right) to toggle scroll
mode.
Double-click to jump to source. Double-click in the preview, and jump
to the start of the corresponding line in the document.
Export documents with Pandoc (including Codebraid output). Simply click
the "Pandoc" button in the status bar (bottom right), or use the "Export
document with Pandoc" command (Ctrl+Shift+P, then type command).
Scroll-sync support for multi-file documents. Pandoc allows you to
divide a document into multiple files that are combined into a single output
document at build time. Codebraid Preview can display such documents as
long as all document files are in the same directory (folder). For
multi-file documents, create a YAML file that lists the document files to be
combined. For example, suppose your document is divided into chapter_1.md
and chapter_2.md, both in the same directory. Simply create a file named
_codebraid_preview.yaml with this contents:
input-files:
- chapter_1.md
- chapter_2.md
Now, when you launch a preview in either chapter_1.md or chapter_2.md,
both files will be combined in the preview. When you scroll the preview,
the editor will automatically switch between chapter_1.md and
chapter_2.md depending on which part of the document you are viewing.
That is, scroll sync works across multiple input files!
Execute code. Codebraid allows
code blocks or inline code in Pandoc Markdown documents to be executed, with
output embedded in the document. Simply add Codebraid attributes to your
code, then click the "Codebraid" button in the status bar (bottom right) or
use the "Run code with Codebraid" command (Ctrl+Shift+P, then type
command).
For example, to execute a Python fenced code block, simply add the
attributes {.python .cb-run} immediately after the opening fence ```,
so that the code block begins with ```{.python .cb-run}. Then click the
Codebraid button. To use a Jupyter kernel for code execution, with a notebook-style display of output, use
```{.python .cb-nb jupyter_kernel=python3} in the first code block to be
executed and ```{.python .cb-nb} in subsequent code blocks.
When you first load a document that uses Codebraid, any cached code output
will automatically be loaded and displayed in the document. The preview
will automatically refresh when you make changes to the document outside of
executed code. However, code never runs automatically. Code execution
requires clicking the "Codebraid" button or using the "Run code with
Codebraid" command.
Requirements
Install Pandoc. The latest version is recommended.
Versions before 2.17.1.1 may work but will have reduced functionality,
including scroll sync issues with YAML metadata.
For code execution, install the latest version of
Codebraid.
By default, documents are treated as Pandoc's commonmark_x format, which is
different from Pandoc's default markdown format. Scroll sync is only
possible with Pandoc's CommonMark-based formats, and commonmark_x is the
most powerful of these.
The Pandoc Roadmap
provides details about commonmark_x features. commonmark_x currently
lacks some markdown features that are summarized below. If you need these
features, you can switch the input format to markdown by modifying the
extension setting codebraid.preview.pandoc.fromFormat. Or you can create a
defaults file _codebraid_preview.yaml in the document directory and set
from: markdown in it. Keep in mind that switching to markdown will
disable scroll sync.
Summary of some key features not present in commonmark_x compared to
markdown:
Citations: Not currently supported, but planned.
Tables: Grid tables, multiline tables, simple tables, and table
captions are not supported but planned. Pipe tables are supported.
LaTeX math: Only $ and $$ are supported as delimiters. Variations
on \(...\) and \[...\] are not supported.
Raw LaTeX: LaTeX cannot just be mixed with Markdown text. Instead, raw
attributes must be used. So instead of text \command text use something
like text `\command`{=tex} text.
LaTeX macros: User-defined LaTeX macros are not expanded by Pandoc
itself before document conversion (the latex_macros extension is not
supported), so the output format must handle macro expansion. This is
primarily important for non-LaTeX formats.
In a document using LaTeX math but targeting a non-LaTeX format like HTML,
this can mean that macro definitions belong in a LaTeX math block and must
be made global. For example, the markdown document
\newcommand{\tuple}[1]{\langle [#1](https://github.com/gpoore/codebraid-preview-vscode/issues/1)\rangle}
$\tuple{a, b, c}$
might become the commonmark_x document
$$
\newcommand{\tuple}[1]{\langle [#1](https://github.com/gpoore/codebraid-preview-vscode/issues/1)\rangle}
\global\let\tuple\tuple
$$
$\tuple{a, b, c}$
The exact details of macro definition processing will depend somewhat on how
LaTeX math is rendered and on the configuration of the renderer.
A note on filters
Scroll sync is provided for CommonMark-based formats using Pandoc's
sourcepos extension. This inserts Div and Span nodes into the Pandoc
AST that contain information about source file origin location in a data-pos
attribute. If you use filters with your documents and want to make sure that
the preview is accurate while retaining scroll sync capabilities, make sure
that your filter skips these nodes and only removes them if empty. For
example, in a Lua filter these nodes can be detected by checking
node.attributes['data-pos'] ~= nil.
Extension settings
codebraid.preview.minBuildInterval [1000]: Minimum interval between
document builds in milliseconds. Builds only occur when there are changes.
codebraid.preview.pandoc.fromFormat [commonmark_x]: Pandoc source
format (--from=FORMAT). Currently, only commonmark_x supports scroll
sync.
codebraid.preview.pandoc.options [none]: Pandoc command-line options. In
the settings GUI, one option per line (for example, --filter FILTER). In
settings.json, an array with one option per element (for example,
["--filter FILTER"]). Pandoc is executed within a shell, so any spaces in
option values must be quoted. Depending on operating system, expansion
and substitution are available. Under Windows, any unquoted option value
beginning with ~/ or ~\ will have the ~ expanded to the user home
directory via os.homedir().
codebraid.preview.pandoc.previewDefaultsFile [_codebraid_preview.yaml]:
Special Pandoc defaults file
in the document directory that is used for preview purposes.
All Pandoc defaults options are supported with one exception. If the
defaults file includes additional external defaults files by setting
defaults, then the following options in those additional external defaults
files will be ignored: input-files, input-file, from, reader, to,
writer, and file-scope. The preview must know the values of these
options to function correctly, and it does not attempt to replicate Pandoc's
system for locating and merging multiple defaults files.
While essentially all defaults options are supported, keep in mind that some
options or option values are irrelevant or inappropriate. The preview is
HTML, so avoid options that do not affect HTML, are incompatible with HTML,
result in non-HTML output, or redirect the output.
If the defaults file is modified within VS Code, the preview will
automatically detect changes and update. If the defaults file is modified
in another editor, close and restart the preview for changes to be applied.
If the defaults file exists and it defines input-files, then the preview
will automatically work with all files in a multi-file document. If the
defaults file defines input-files (or input-file), then it will only be
applied to the specified files; it will be ignored for other files.
If the defaults file defines input-files (or input-file), all specified
files must be in the same directory with the defaults file. Document files
in subdirectories are not supported.
codebraid.preview.pandoc.showRaw [true]: Display a verbatim
representation of non-HTML raw content {=format} in the preview.
Codebraid configuration
When Codebraid is used to run code, the codebraid executable is found by
searching the following locations.
If a Python interpreter is set in VS Code, the interpreter installation is
checked for a codebraid executable.
Notice that a Python interpreter can be set at the file level or workspace
level (Ctrl+Shift+P, then Python: Select Interpreter, or configure
python.defaultInterpreterPath in a workspace settings.json). A Python
interpreter can also be configured in global User Settings (File,
Preferences, Settings, Python: Default Interpreter Path). Only the first
Python interpreter that is set in the file/workspace/global sequence is
checked for a codebraid executable.
For more details about configuring Python in VS Code, see
https://code.visualstudio.com/docs/python/environments.
If a Python interpreter is not set, or its installation does not include a
codebraid executable, then the first codebraid executable on PATH is
used. There will be a warning message if a Python interpreter is set but
does not include codebraid, so that codebraid on PATH is used as a
fallback.
If the codebraid executable is part of an
Anaconda installation, it is
launched via conda run so that the relevant conda environment is activated.
For other environments and installations, the codebraid executable is run
directly.
Security
The HTML preview is displayed using a webview. A content security policy is
used to restrict what is possible in the webview. Inline scripts and styles
are allowed to support features like KaTeX math. Loading external resources
not associated with the extension is disabled.
Code is never automatically executed with Codebraid. Code is only ever
executed when a Codebraid class is added to a code block or inline code, and
then the "Codebraid" button is clicked (or the "Run code with Codebraid"
command is invoked).
Supporting this project
Codebraid Preview is open-source software released under the BSD 3-Clause
License. If you use it regularly, please consider supporting further
development through GitHub Sponsors.
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