Add LSP-Extensions.md

LSP-Extensions.md

@@ -0,0 +1,79 @@
+## Cross reference extensions
+
+Aside from definitions/references/workspace symbol, ccls provides some LSP extensions that find base/derived classes/methods, vars of a type, callers of a function.
+
+### [`$ccls/vars`](https://github.com/MaskRay/ccls/blob/master/src/messages/ccls_call.cc)
+
+It can be seen as a specialized `textDocument/references`. It finds all variables when the cursor is at a type of a variable (the type of the variable will be used). Whether local variables/parameters/struct members are returned can be specified with `kind`.
+
+* params: `TextDocumentPositionParams` extended with `kind`
+* return: `Location[]`
+
+### [`$ccls/call`](https://github.com/MaskRay/ccls/blob/master/src/messages/ccls_call.cc)
+
+Find callers (`callee: false`, default) or callees (`callee: true`) when the cursor is at a function.
+
+The method returns either a flattened `Location[]`, or a hierarchical type.
+
+#### `hierarchy: false` (default)
+
+* params: `TextDocumentPositionParams` extended with `callee, callType`
+* return: `Location[]`
+
+#### `hierarchy: true`
+
+* initial params: `TextDocumentPositionParams` extended with `callee, callType`. The result includes `id` and `kind` which are used to expand a node.
+* params: `id, kind, callee, callType`
+
+Optional `levels` and `qualified` can be used to customize the hierarchy.
+
+### [`$ccls/inheritance`](https://github.com/MaskRay/ccls/blob/master/src/messages/ccls_inheritance.cc)
+
+Find base classes (`derived: false`, default) or derived classes (`derived: true`).
+
+It can also used to jump between the primary template and partial specializations.
+
+#### `hierarchy: false` (default)
+
+* params: `TextDocumentPositionParams` extended with `derived`
+* return: `Location[]`
+
+#### `hierarchy: true`
+
+* initial params: `TextDocumentPositionParams` extended with `derived`. The result includes `id` and `kind` which are used to expand a node.
+* params: `id, kind, derived`
+
+Optional `levels` and `qualified` can be used to customize the hierarchy.
+
+### [`ccls/member`](https://github.com/MaskRay/ccls/blob/master/src/messages/ccls_member.cc)
+
+Find member variables/functions/types when the cursor is at a class/struct/union or a variable (the type of which will be used). Find local variables when the cursor is at a function.
+
+* `kind: 4` (default), member variables are returned.
+* `kind: 3`, member functions are returned.
+* `kind: 2`, member types are returned.
+
+#### `hierarchy: false` (default)
+
+* params: `TextDocumentPositionParams` extended with `derived`
+* return: `Location[]`
+
+#### `hierarchy: true`
+
+* initial params: `TextDocumentPositionParams` extended with `derived`. The result includes `id` and `kind` which are used to expand a node.
+* params: `id, kind, derived`
+
+Returned nodes can be furthe expanded if `kind: 4`.
+
+Optional `levels` and `qualified` can be used to customize the hierarchy.
+
+### [`$ccls/navigate`](https://github.com/MaskRay/ccls/blob/master/src/messages/ccls_navigate.cc)
+
+Semantic movement among declarations.
+
+* params: `TextDocumentPositionParams` extended with `direction`. The allowed values of `direction`:
+  + `"U"`: parent
+  + `"D"`: first child
+  + `"L"`: left sibling
+  + `"R"`: right sibling
+* return: `Location[]`

_Sidebar.md

@@ -18,4 +18,5 @@
 * [[Customization]]
 * [[Debugging]]
 * [[FAQ]]
+* [[LSP Extensions]]
 * [[LSP]]