add some Rust patterns

.grit/grit.yaml

@@ -1,3 +1,14 @@
 version: 0.0.1
 patterns:
-  - name: github.com/getgrit/stdlib#*
+  - name: github.com/getgrit/stdlib#*
+  - name: no_println_in_lsp
+    description: Don't use println!() in LSP code, it breaks the LSP stdio protocol.
+    level: error
+    body: |
+      engine marzano(0.1)
+      language rust
+
+      `println!($_)` => .  where {
+        $filename <: not includes "test.rs",
+        $absolute_filename <: includes "apps/marzano/lsp",
+      }

.grit/patterns/flushable_unwrap.md

@@ -0,0 +1,23 @@
+# Force flushing
+
+Prevent returning without flushing the emitter in `apply_pattern.rs`.
+
+```grit
+language rust
+
+pattern flushable_return() {
+  `$expression?` where {
+    $expression <: not includes "flush",
+    $expression <: not within `let mut emitter: MessengerVariant = $_;`,
+    $expression => `flushable_unwrap!(emitter, $expression)`
+  }
+}
+
+file(name=includes "apply_pattern.rs", $body) where {
+  $body <: contains `pub(crate) async fn run_apply_pattern(
+      $_
+  ) -> Result<()> { $func }` where {
+    $func <: contains flushable_return()
+  }
+}
+```

.grit/patterns/no_panic.md

@@ -0,0 +1,28 @@
+---
+level: info
+---
+
+# Avoid panic
+
+Panics should be avoided in core Grit code. Instead, use `?` to propagate errors.
+
+```grit
+language rust
+
+file($name, $body) where {
+  $name <: includes "marzano/lsp",
+  $body <: contains `$foo.unwrap()` => `$foo?`,
+}
+```
+
+## Sample
+
+```rust
+// @filename: marzano/lsp/foo.rs
+let x = bar().unwrap();
+```
+
+```rust
+// @filename: marzano/lsp/foo.rs
+let x = bar()?;
+```