Add more info about analysis tool (#7209)

* Add more info about analysis tool

* Update local repo install instruction

Author: nojaf

analysis/README.md

@@ -12,15 +12,89 @@ See main CONTRIBUTING.md's repo structure. Additionally, `examples/` is a conven
 
 ## Usage
 
-At root:
-```sh
-./rescript-editor-analysis.exe --help
-
-# or
-
+```shell
 dune exec -- rescript-editor-analysis --help
 ```
 
 ## History
 
 This project is based on a fork of [Reason Language Server](https://github.com/jaredly/reason-language-server).
+
+## Tests
+
+### Prerequisites
+
+- Ensure the compiler is built (`make build` in the repository root).
+- Ensure the library is built (`make lib` in the repository root).
+
+### Running the Tests
+
+Run `make test` in `tests/analysis_tests/tests`.
+
+### Key Concept
+
+The tests in the `tests/analysis_tests/tests` folder are based on the `dune exec -- rescript-editor-analysis test` command. This special subcommand processes a file and executes specific editor analysis functionality based on special syntax found in code comments.
+
+Consider the following code:
+
+```res
+let a = 5
+// a.
+//   ^com
+```
+
+After building the ReScript project (**⚠️ this is a requirement**), you can execute `dune exec -- rescript-editor-analysis test Sample.res`, and completion will be performed for the cursor position indicated by `^`. The `com` directive requests completion. To see other commands, check out the pattern match in the `test` function in [Commands.ml](./src/Commands.ml).
+
+> [!WARNING]
+> Ensure there are no spaces in the code comments, as the commands are captured by a regular expression that expects spaces and not tabs!
+
+Here’s how it works: once a command is found in a comment, a copy of the source file is created inside a temporary directory, where the line above `^com` is uncommented. The corresponding analysis functionality is then processed, typically with `~debug:true`. With debug enabled, code paths like
+
+```ml
+if Debug.verbose () then
+      print_endline "[complete_typed_value]--> Tfunction #other";
+```
+
+will print to stdout. This is helpful for observing what happens during the analysis.
+
+When you run `make test` (from the `tests/analysis_tests` folder), `dune exec -- rescript-editor-analysis test <file>` will be executed for each `*.res` file in `analysis/tests/src`. The stdout will be compared to the corresponding `analysis/tests/src/expected` file. If `git diff` indicates changes, `make test` will fail, as these differences might be unintentional.
+
+## Testing on Your Own Projects
+
+To use a local version of `rescript-editor-analysis`, the targeted project needs to be compiled with the local compiler.
+
+Install your local ReScript with `npm i /path/to/your-local-rescript-repo`.
+Reinstall the dependencies and run `npx rescript` in your project. This ensures the project is compiled with the same compiler version that the `rescript-editor-analysis` will process.
+
+## Debugging
+
+It is possible to debug `analysis` via [ocamlearlybird](https://github.com/hackwaly/ocamlearlybird).
+
+1. Install `opam install earlybird`.
+2. Install the [earlybird extension](https://marketplace.visualstudio.com/items?itemName=hackwaly.ocamlearlybird).
+3. Create a launch configuration (`.vscode/launch.json`):
+
+```json
+{
+    "version": "0.2.0",
+    "configurations": [
+        {
+            "name": "Debug analysis",
+            "type": "ocaml.earlybird",
+            "request": "launch",
+            "program": "${workspaceFolder}/_build/default/analysis/bin/main.bc",
+            "stopOnEntry": true,
+            "cwd": "/projects/your-project",
+            "env": {
+                "CAML_LD_LIBRARY_PATH": "${workspaceFolder}/_build/default/compiler/ext"
+            },
+            "arguments": [
+                "test",
+                "src/Main.res"
+            ]
+        }
+    ]
+}
+```
+
+The `CAML_LD_LIBRARY_PATH` environment variable is required to tell OCaml where `dllext_stubs.so` can be loaded from.