Docs: add separate page for language server features

Signed-off-by: Anders Eknert <anders@styra.com>
StyraInc · Jul 1, 2024 · 24bc53e · 24bc53e
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diff --git a/README.md b/README.md
@@ -626,20 +626,30 @@ symbols helping you easily navigate the Rego code in your workspace.
 
 The Regal language server currently supports the following LSP features:
 
-- [x] Diagnostics (linting)
-- [x] Hover (for inline docs on built-in functions)
-- [x] Go to definition (ctrl/cmd + click on a reference to go to definition)
-- [x] Folding ranges (expand/collapse blocks, imports, comments)
-- [x] Document and workspace symbols (navigate to rules, functions, packages)
-- [x] Inlay hints (show names of built-in function arguments next to their values)
-- [x] Formatting
-- [x] Code completions
-- [x] Code actions (quick fixes for linting issues)
+- [x] [Diagnostics](https://github.com/StyraInc/regal/blob/main/docs/language-server.md#diagnostics) (linting)
+- [x] [Hover](https://github.com/StyraInc/regal/blob/main/docs/language-server.md#hover)
+      (for inline docs on built-in functions)
+- [x] [Go to definition](https://github.com/StyraInc/regal/blob/main/docs/language-server.md#go-to-definition)
+      (ctrl/cmd + click on a reference to go to definition)
+- [x] [Folding ranges](https://github.com/StyraInc/regal/blob/main/docs/language-server.md#folding-ranges)
+      (expand/collapse blocks, imports, comments)
+- [x] [Document and workspace symbols](https://github.com/StyraInc/regal/blob/main/docs/language-server.md#document-and-workspace-symbols)
+      (navigate to rules, functions, packages)
+- [x] [Inlay hints](https://github.com/StyraInc/regal/blob/main/docs/language-server.md#inlay-hints)
+      (show names of built-in function arguments next to their values)
+- [x] [Formatting](https://github.com/StyraInc/regal/blob/main/docs/language-server.md#formatting)
+- [x] [Code completions](https://github.com/StyraInc/regal/blob/main/docs/language-server.md#code-completions)
+- [x] [Code actions](https://github.com/StyraInc/regal/blob/main/docs/language-server.md#code-actions)
+      (quick fixes for linting issues)
   - [x] [opa-fmt](https://docs.styra.com/regal/rules/style/opa-fmt)
   - [x] [use-rego-v1](https://docs.styra.com/regal/rules/imports/use-rego-v1)
   - [x] [use-assignment-operator](https://docs.styra.com/regal/rules/style/use-assignment-operator)
   - [x] [no-whitespace-comment](https://docs.styra.com/regal/rules/style/no-whitespace-comment)
 
+See the
+[documentation page for the language server](https://github.com/StyraInc/regal/blob/main/docs/language-server.md)
+for an extensive overview of all features, and their meaning.
+
 See the [Editor Support](/docs/editor-support.md) page for information about Regal support in different editors.
 
 ## Resources

diff --git a/docs/assets/lsp/codeaction.png b/docs/assets/lsp/codeaction.png
diff --git a/docs/assets/lsp/completion.png b/docs/assets/lsp/completion.png
diff --git a/docs/assets/lsp/diagnostics.png b/docs/assets/lsp/diagnostics.png
diff --git a/docs/assets/lsp/documentsymbols.png b/docs/assets/lsp/documentsymbols.png
diff --git a/docs/assets/lsp/documentsymbols2.png b/docs/assets/lsp/documentsymbols2.png
diff --git a/docs/assets/lsp/folding.png b/docs/assets/lsp/folding.png
diff --git a/docs/assets/lsp/format.png b/docs/assets/lsp/format.png
diff --git a/docs/assets/lsp/hover.png b/docs/assets/lsp/hover.png
diff --git a/docs/assets/lsp/inlay.png b/docs/assets/lsp/inlay.png
diff --git a/docs/language-server.md b/docs/language-server.md
@@ -0,0 +1,144 @@
+# Language Server
+
+In order to support Rego policy development in editors like
+[VS Code](https://github.com/open-policy-agent/vscode-opa) or [Zed](https://github.com/StyraInc/zed-rego),
+Regal provides an implementation of the
+[Language Server Protocol](https://microsoft.github.io/language-server-protocol/) (LSP) for Rego.
+
+This implementation allows the result of linting to be presented directly in your editor as you work on your policies,
+and without having to call Regal from the command line. The language server however provides much more than just
+linting!
+
+## Features
+
+The Regal language server currently supports the following LSP features:
+
+### Diagnostics
+
+Diagnostics are errors, warnings, and information messages that are shown in the editor as you type. Regal currently
+uses diagnostics to present users with either parsing errors in case of syntax issues, and linter violations reported
+by the Regal linter.
+
+<img
+  src="assets/lsp/diagnostics.png"
+  alt="Screenshot of diagnostics as displayed in Zed"/>
+
+Future versions of Regal may include also [compilation errors](https://github.com/StyraInc/regal/issues/745) as part of
+diagnistics messages.
+
+### Hover
+
+The hover feature means that moving the mouse over certain parts of the code will bring up a tooltip with documentation
+for the code under the cursor. This is particularly useful for built-in functions, as it allows you to quickly look up
+the meaning of the function, and the arguments it expects.
+
+<img
+  src="assets/lsp/hover.png"
+  alt="Screenshot of hover as displayed in VS Code"/>
+
+The Regal language server currently supports hover for all built-in functions OPA provides.
+
+### Go to definition
+
+Go to definition allows references to rules and functions to be clicked on (while holding `ctrl/cmd`), and the editor
+will navigate to the definition of the rule or function.
+
+### Folding ranges
+
+Regal provides folding ranges for any policy being edited. Folding ranges are areas of the code that can be collapsed
+or expanded, which may be useful for hiding content that is not relevant to the current task.
+
+<img
+  src="assets/lsp/folding.png"
+  alt="Screenshot of folding ranges as displayed in Zed"/>
+
+Regal supports folding ranges for blocks, imports and comments.
+
+### Document and workspace symbols
+
+Document and workspace symbols allow policy authors to quickly scan and navigate to symbols (like rules and functions)
+anywhere in the document or workspace.
+
+<img
+  src="assets/lsp/documentsymbols.png"
+  alt="Screenshot showing search on workspace symbols in Zed"/>
+
+VS Code additionally provides an "Outline" view, which is a nice visual representation of the symbols in the document.
+
+<img
+  src="assets/lsp/documentsymbols2.png"
+  alt="Screenshot showing outline view of document symbols in VS Code"/>
+
+### Inlay hints
+
+Inlay hints help developers quickly understand the meaning of the arguments passed passed to functions in the code,
+by showing the name of the argument next to the value. Inlay hints can additionally be hovered for more information,
+like the expected type of the argument.
+
+<img
+  src="assets/lsp/inlay.png"
+  alt="Screenshot showing inlay hints in VS Code/>
+
+Regal currently supports inlay hints for all built-in functions. Future versions may support inlay hints for
+user-defined functions too.
+
+### Formatting
+
+Regal uses the `opa fmt` formatter for formatting Rego. This is made available as a command in editors, but also via
+a [code action](#code-actions) when unformatted files are encountered.
+
+<img
+  src="assets/lsp/format.png"
+  alt="Screenshot of diagnostics as displayed in Zed"/>
+
+### Code completions
+
+Code completions, or suggestions, is likely one of the most useful features of the Regal language server. And best of
+all, you don't need to do anything special for it to happen! Just write your policy as you normally would, and Regal
+will provide suggestions for anything that could be relevant in the context that you're typing. This could for example
+be suggestions for:
+
+- Built-in functions
+- Local variables
+- Imported packages
+- References from anywhere in the workspace
+- And much more!
+
+<img
+  src="assets/lsp/completion.png"
+  alt="Screenshot of completion suggestions as displayed in Zed"/>
+
+New completion providers are added continuosly, so if you have a suggestion for a new completion, please
+[open an issue](https://github.com/StyraInc/regal/issues)!
+
+### Code actions
+
+Code actions are actions that appear in the editor when certain conditions are met. One example would be "quick fixes"
+that may appear when a linter rule has been violated. Code actions can be triggered by clicking on the lightbulb icon
+that appears on the line with a diagnostic message, or by pressing `ctrl/cmd + .` when the cursor is on the line.
+
+<img
+  src="assets/lsp/codeaction.png"
+  alt="Screenshot of code action displayed in Zed"/>
+
+Regal currently provides quick fix code actions for the following linter rules:
+
+- [opa-fmt](https://docs.styra.com/regal/rules/style/opa-fmt)
+- [use-rego-v1](https://docs.styra.com/regal/rules/imports/use-rego-v1)
+- [use-assignment-operator](https://docs.styra.com/regal/rules/style/use-assignment-operator)
+- [no-whitespace-comment](https://docs.styra.com/regal/rules/style/no-whitespace-comment)
+
+## Unsupported features
+
+See the
+[open issues](https://github.com/StyraInc/regal/issues?q=is%3Aissue+is%3Aopen+label%3A%22language+server+protocol%22)
+with the `language server protocol` label for a list of features that are not yet supported by the Regal language
+server, but that are planned for the future. If you have suggestions for anything else, please create a new issue!
+
+Also note that not all clients (i.e. editors) may support all features of a language server! See the
+[editor support](/docs/editor-support.md) page for information about Regal support in different editors.
+
+## Community
+
+If you'd like to discuss the Regal's language server, or just talk about Regal in general, please join us in the
+`#regal` channel in the Styra Community [Slack](https://communityinviter.com/apps/styracommunity/signup)!