Render the expansion of snippets as their docs

crates/ide_completion/src/completions/snippet.rs

@@ -1,5 +1,6 @@
 //! This file provides snippet completions, like `pd` => `eprintln!(...)`.
 
+use hir::Documentation;
 use ide_db::helpers::{insert_use::ImportScope, SnippetCap};
 use syntax::T;
 
@@ -109,7 +110,9 @@ fn add_custom_completions(
                 Some(imports) => imports,
                 None => return,
             };
-            let mut builder = snippet(ctx, cap, &trigger, &snip.snippet());
+            let body = snip.snippet();
+            let mut builder = snippet(ctx, cap, &trigger, &body);
+            builder.documentation(Documentation::new(format!("```rust\n{}\n```", body)));
             for import in imports.into_iter() {
                 builder.add_import(import);
             }