Make sure error outputs are what we expect (#114)

I've added a `--verify` mode to `tutorial_generator`: expected error
outputs are now committed to `.git` and we verify, in CI, that the
auto-generated ones match what we expect.

This ensures that we never see again a regression like the one we fixed
in #113: the step was failing as expected but with a completely
different error from the one we wanted.

.github/workflows/docs.yml

@@ -110,7 +110,7 @@ jobs:
       - name: Generate quickstart tutorial
         run: |
           cd doc_examples/quickstart
-          tutorial_generator
+          tutorial_generator --verify
       - name: Set up QEMU
         uses: docker/setup-qemu-action@v3
       - name: Set up Docker Buildx

doc_examples/quickstart/.gitignore

@@ -1,3 +1,4 @@
 *
+!*.snap
 !*.patch
 !tutorial.yml

doc_examples/quickstart/05-error.snap

@@ -0,0 +1,23 @@
+ERROR: 
+  × I can't invoke your request handler, `demo::routes::greet::greet`, because it needs an
+  │ instance of `demo::user_agent::UserAgent` as input, but I can't find a constructor for that
+  │ type.
+  │
+  │     ╭─[demo/src/blueprint.rs:14:1]
+  │  14 │     bp.route(GET, "/api/ping", f!(crate::routes::status::ping));
+  │  15 │     bp.route(GET, "/api/greet/:name", f!(crate::routes::greet::greet));
+  │     ·                                       ───────────────┬───────────────
+  │     ·                                                      ╰── The request handler was registered here
+  │  16 │     bp
+  │     ╰────
+  │     ╭─[demo/src/routes/greet.rs:13:1]
+  │  13 │ 
+  │  14 │ pub fn greet(params: RouteParams<GreetParams>, user_agent: UserAgent) -> Response {
+  │     ·                                                            ────┬────
+  │     ·                                                                ╰── I don't know how to construct an instance of this input parameter
+  │  15 │     if let UserAgent::Unknown = user_agent {
+  │     ╰────
+  │   help: Register a constructor for `demo::user_agent::UserAgent`
+
+Error: `pavex_cli` exited with a non-zero status code: 1
+error: Failed to run `bp`, the code generator for package `demo_server_sdk`

doc_examples/quickstart/07-error.snap

@@ -0,0 +1,16 @@
+ERROR: 
+  × You registered a constructor that returns a `Result`, but you did not register an error
+  │ handler for it. If I don't have an error handler, I don't know what to do with the error when
+  │ the constructor fails!
+  │
+  │     ╭─[demo/src/blueprint.rs:12:1]
+  │  12 │     bp.constructor(
+  │  13 │         f!(crate::user_agent::UserAgent::extract),
+  │     ·         ────────────────────┬────────────────────
+  │     ·                             ╰── The fallible constructor was registered here
+  │  14 │         Lifecycle::RequestScoped,
+  │     ╰────
+  │   help: Add an error handler via `.error_handler`
+
+Error: `pavex_cli` exited with a non-zero status code: 1
+error: Failed to run `bp`, the code generator for package `demo_server_sdk`

doc_examples/quickstart/tutorial.yml

@@ -10,14 +10,14 @@ steps:
   - patch: "05-bis.patch"
     commands:
       - command: "cargo px c -q"
-        outcome: "failure"
-        save_at: "05-error.txt"
+        expected_outcome: "failure"
+        expected_output_at: "05-error.snap"
   - patch: "06.patch"
   - patch: "07.patch"
     commands:
       - command: "cargo px c -q"
-        outcome: "failure"
-        save_at: "07-error.txt"
+        expected_outcome: "failure"
+        expected_output_at: "07-error.snap"
   - patch: "08.patch"
   - patch: "09.patch"
   - patch: "10.patch"

doc_examples/tutorial_generator/Cargo.toml

@@ -10,3 +10,5 @@ serde_yaml = "0.9.27"
 serde_path_to_error = "0.1"
 serde = { version = "1", features = ["derive"] }
 run_script = "0.10"
+similar = { version = "2.3", features = ["inline"] }
+console = "0.15.1"