Isabelle Prover IDE support

This extension connects VSCode to the Isabelle Prover IDE infrastructure: it requires Isabelle2021-1.

The implementation is centered around the VSCode Language Server protocol, but with many add-ons that are specific to VSCode and Isabelle/PIDE.

Screenshot

[Isabelle/VSCode]

Notable Features

Static syntax tables for Isabelle .thy and .ML files.
Implicit dependency management of sources, subject to changes of theory files within the editor, as well as external file-system events.
Implicit formal checking of theory files, using the cursor position of the active editor panel as indication for relevant spots.
Text overview lane with formal status of prover commands (unprocessed, running, error, warning).
Prover messages within the source text (errors/warnings and information messages).
Semantic text decorations: colors for free/bound variables, inferred types etc.
Visual indication of formal scopes and hyperlinks for formal entities.
Implicit proof state output via the VSCode message channel "Isabelle Output".
Explicit proof state output via separate GUI panel (command isabelle.state).
HTML preview via separate GUI panel (command isabelle.preview).
Rich completion information: Isabelle symbols (e.g. \forall or \<forall>), outer syntax keywords, formal entities, file-system paths, BibTeX entries etc.
Spell-checking of informal texts, including dictionary operations: via the regular completion dialog.

Requirements

Isabelle/VSCode Installation

Download Isabelle2021-1 from https://isabelle.in.tum.de/website-Isabelle2021-1 or any of its mirror sites.
Unpack and run the main Isabelle/jEdit application as usual, to ensure that the logic image is built properly and Isabelle works as expected.
Download and install VSCode from https://code.visualstudio.com
Open the VSCode Extensions view and install the following:
- Isabelle (needs to fit to the underlying Isabelle release).
- Prettify Symbols Mode (important for display of Isabelle symbols).
- bibtexLanguage (optional): it gives .bib a formal status, thus @{cite} antiquotations become active for completion and hyperlinks.
Open the dialog Preferences / User settings and provide the following entries in the second window, where local user additions are stored:
- On all platforms: isabelle.home needs to point to the main Isabelle directory ($ISABELLE_HOME).
- On Windows: use drive-letter and backslashes for isabelle.home above. When running from a bare repository clone (not a development snapshot), isabelle.cygwin_home needs to point to a suitable Cygwin installation.
Examples:
- Linux:
```
"isabelle.home": "/home/makarius/Isabelle2021-1"
```
- Mac OS X:
```
"isabelle.home": "/Users/makarius/Isabelle.app/Isabelle2021-1"
```
- Windows:
```
"isabelle.home": "C:\\Users\\makarius\\Isabelle2021-1"
```
Restart the VSCode application to ensure that all extensions are properly initialized and user settings are updated. Afterwards VSCode should know about .thy files (Isabelle theories) and .ML files (Isabelle/ML modules).

The Isabelle extension is initialized when the first Isabelle file is opened. It requires a few seconds to start up: a small popup window eventually says "Welcome to Isabelle ...". If that fails, there might be something wrong with isabelle.home from above, or the Isabelle distribution does not fit to the version of the VSCode extension from the Marketplace.

Support for Isabelle symbols

Isabelle symbols like \<forall> are rendered using the extension Prettify Symbols Mode, which needs to be installed separately.

In addition, the following user settings should be changed in the Preferences / User settings dialog of VSCode:

"prettifySymbolsMode.substitutions": [
  {
    "language": "isabelle",
    "revealOn": "none",
    "adjustCursorMovement": true,
    "prettyCursor": "none",
    "substitutions": []
  },
  {
    "language": "isabelle-ml",
    "revealOn": "none",
    "adjustCursorMovement": true,
    "prettyCursor": "none",
    "substitutions": []
  }]

Actual symbol replacement tables are provided by the prover process on startup, based on the usual etc/symbols specifications of the Isabelle installation.

Further Preferences

Preferred Color Theme: Light+ (default light)
Alternative Color Theme: Dark+ (default dark) – with restrictions: some color combinations don't work out properly.

Recommended changes to default VSCode settings:

"editor.acceptSuggestionOnEnter": "off",
"editor.lineNumbers": "off",
"editor.renderIndentGuides": false,
"editor.rulers": [80, 100],
"editor.wordBasedSuggestions": true,

Known Limitations of Isabelle/VSCode

Lack of specific support for the Isabelle fonts: these need to be manually installed on the system and configured for VSCode (see also $ISABELLE_FONTS within the Isabelle environment).

Note: As the Isabelle fonts continue to evolve, installed versions need to be updated according to each new Isabelle version.
Isabelle symbols are merely an optical illusion: it would be better to make them a first-class Unicode charset as in Isabelle/jEdit.
Isabelle symbol abbreviations like "-->" are not accepted by VSCode.
Lack of formal editor perspective in VSCode: only the cursor position is used (with some surrounding lines of text).
Lack of formal markup in prover messages and popups.
Lack of pretty-printing (logical line breaks) according to window and font dimensions.
Lack of GUI panels for Sledgehammer, Query operations etc.
Big theory files may cause problems to the VSCode rendering engine, since messages and text decorations are applied to the text as a whole (cf. the minimap view).

Isabelle2021-1

Makarius Wenzel