Add docs

Author: vsrs

docs/user/manual.adoc

@@ -109,18 +109,6 @@ Here are some useful self-diagnostic commands:
 * To log all LSP requests, add `"rust-analyzer.trace.server": "verbose"` to the settings and look for `Server Trace` in the panel.
 * To enable client-side logging, add `"rust-analyzer.trace.extension": true` to the settings and open the `Console` tab of VS Code developer tools.
 
-==== Special `when` clause context for keybindings.
-You may use `inRustProject` context to configure keybindings for rust projects only. For example:
-[source,json]
-----
-{
-  "key": "ctrl+i",
-  "command": "rust-analyzer.toggleInlayHints",
-  "when": "inRustProject"
-}
-----
-More about `when` clause contexts https://code.visualstudio.com/docs/getstarted/keybindings#_when-clause-contexts[here].
-
 === rust-analyzer Language Server Binary
 
 Other editors generally require the `rust-analyzer` binary to be in `$PATH`.
@@ -337,3 +325,49 @@ They are usually triggered by a shortcut or by clicking a light bulb icon in the
 Cursor position or selection is signified by `┃` character.
 
 include::./generated_assists.adoc[]
+
+== Editor Features
+=== VS Code
+==== Special `when` clause context for keybindings.
+You may use `inRustProject` context to configure keybindings for rust projects only. For example:
+[source,json]
+----
+{
+  "key": "ctrl+i",
+  "command": "rust-analyzer.toggleInlayHints",
+  "when": "inRustProject"
+}
+----
+More about `when` clause contexts https://code.visualstudio.com/docs/getstarted/keybindings#_when-clause-contexts[here].
+
+=== Setting runnable environment variables
+You can use "rust-analyzer.runnableEnv" setting to define runnable environment-specific substitution variables.
+The simplest way for all runnables in a bunch:
+[source,jsonc]
+---
+"rust-analyzer.runnableEnv": {
+    "RUN_SLOW_TESTS": "1"
+}
+---
+
+Or it is possible to specify vars more granularly:
+[source,jsonc]
+---
+"rust-analyzer.runnableEnv": [
+    {
+        // "mask": null, // null mask means that this rule will be applied for all runnables
+        env: {
+             "APP_ID": "1",
+             "APP_DATA": "asdf"
+        }
+    },
+    {
+        "mask": "test_name",
+        "env": {
+             "APP_ID": "2", // overwrites only APP_ID
+        }
+    }
+]
+---
+
+You can use any valid RegExp as a mask. Also note that a full runnable name is something like *run bin_or_example_name*, *test some::mod::test_name* or *test-mod some::mod*, so it is possible to distinguish binaries, single tests, and test modules with this masks: `"^run"`, `"^test "` (the trailing space matters!), and `"^test-mod"` respectively.