docs: document dual-LSP setup for Rust + Slint development

editors/README.md

@@ -10,6 +10,67 @@ the Language Server Protocol (LSP)
 (see its [README.md](../tools/lsp/README.md) for more info on how to install it).
 If you do test your editor with it, we would be happy to accept a pull request that adds instructions here.
 
+## Using Slint with Rust Projects
+
+When developing Slint applications in Rust, you'll typically use **two language servers** running simultaneously:
+
+| Language Server | Handles | Features |
+|----------------|---------|----------|
+| **rust-analyzer** | `.rs` files | Rust completions, diagnostics, go-to-definition, refactoring |
+| **slint-lsp** | `.slint` files and `slint!` macros | Slint completions, diagnostics, live preview, formatting |
+
+### How They Work Together
+
+Both language servers run independently and don't communicate with each other. This means:
+
+- **In `.slint` files**: Only slint-lsp is active, providing full Slint language support
+- **In `.rs` files**: Both are active
+  - rust-analyzer handles Rust code outside the `slint!` macro
+  - slint-lsp detects `slint!` macro content and provides Slint features within it
+
+### Editor Setup for Rust + Slint
+
+Most editors handle multiple language servers automatically. Install both:
+
+```sh
+# Install rust-analyzer (if not already installed via rustup)
+rustup component add rust-analyzer
+
+# Install slint-lsp
+cargo install slint-lsp
+```
+
+Then configure your editor for both (see editor-specific sections below).
+
+### Features and Limitations
+
+**What works well:**
+- Full Slint language support in `.slint` files
+- Slint completions and diagnostics inside `slint!` macros in Rust files
+- Independent Rust analysis by rust-analyzer
+- Live preview of components
+
+**Current limitations:**
+- No cross-language go-to-definition (can't jump from Rust `component.get_property()` to Slint property definition)
+- No unified diagnostics (errors shown separately by each LSP)
+- The `slint!` macro uses identifier syntax (`foo-bar`) that differs from Rust (`foo - bar`). In rust-analyzer, adjacent identifiers with dashes are treated as single identifiers, which is usually correct for Slint code.
+
+### Troubleshooting
+
+**rust-analyzer shows errors in `slint!` macro:**
+This can happen because rust-analyzer expands the macro differently than rustc. These errors are usually false positives - check that `cargo build` succeeds.
+
+**Completions not working in `slint!` macro:**
+Ensure slint-lsp is running. In VS Code, check the Output panel for "Slint Language Server". In other editors, verify the LSP process is started.
+
+**Performance issues:**
+If your editor feels slow, rust-analyzer's macro expansion may be the cause. You can disable proc-macro expansion in rust-analyzer settings, though this will reduce Rust-side analysis quality:
+```json
+{
+  "rust-analyzer.procMacro.enable": false
+}
+```
+
 ## Editors
 
 - [Visual Studio Code](#visual-studio-code)