Use trybuild for testing macros (#423)

Author: jayvdb

.editorconfig

@@ -46,3 +46,7 @@ indent_style = unset
 [HELP.md]
 max_line_length = 400
 trim_trailing_whitespace = false
+
+[*.stderr]
+indent_size = unset
+max_line_length = unset

.github/workflows/ci.yml

@@ -121,12 +121,16 @@ jobs:
       run: cd butane_test_helper && cargo +stable test --all-features
     - name: Test Core
       run: cd butane_core && cargo +stable test --all-features
-    - name: Test Codegen
-      run: cd butane_codegen && cargo +stable test --all-features
     - name: Test CLI
       run: cd butane_cli && cargo +stable test --all-features
     - name: Test
       run: cargo +stable test -p butane_tests --all-features
+    - name: Test using trybuild
+      run: cargo +stable test -p trybuild_tests
+    - name: Test doctests
+      run: |
+        cargo +stable test -p butane_codegen --all-features
+        cargo +stable test -p butane --all-features
     - name: Check example migrations have been updated
       run: |
         set -ex

.gitignore

@@ -7,6 +7,7 @@ butane.code_workspace.code-workspace
 .vscode/tasks.json
 butane_codegen/.butane
 butane/tests/.butane
+trybuild_tests/tests/Cargo.toml
 db.sqlite
 tmp_pg
 *.db

CONTRIBUTING.md

@@ -94,10 +94,23 @@ cargo test
 Run tests for a specific package:
 
 ```bash
-cargo test -p butane
 cargo test -p butane_core
+cargo test -p butane  # doctests only
+cargo test -p butane_tests
+cargo test -p trybuild_tests
 ```
 
+If you are enhancing `butane_codegen`, please create tests in [`trybuild_tests`](trybuild_tests/)
+instead of `butane_codegen`.
+
+## Development notes
+
+There is a cyclic test dependency between `butane_test_helper` and `butane_core`.
+
+`butane_test_helper` uses `butane_core` in its library.
+
+`butane_core` uses `butane_test_helper` in its tests.
+
 ## Code Quality
 
 Before submitting a PR, you may use the following commands locally to ensure that your code passes all checks:

Cargo.lock

@@ -14,6 +14,7 @@ members = [
   "examples/getting_started",
   "examples/getting_started_async",
   "examples/reserved-words",
+  "trybuild_tests",
 ]
 
 [workspace.package]

Cargo.toml

@@ -24,3 +24,7 @@ syn = { workspace = true }
 
 [lib]
 proc-macro = true
+# When `cargo test` & `cargo nextest run` are run at the top of the workspace,
+# they fail if `test = true` here.
+# See https://github.com/Electron100/butane/issues/419
+test = false

butane_codegen/Cargo.toml

@@ -17,8 +17,8 @@ use syn::{Expr, Ident};
 
 mod filter;
 
-#[cfg(test)]
-mod test_field_type;
+// Note: butane_codegen is a proc-macro crate and cannot have unit tests
+// Tests for derive macros should be in butane_core or integration tests
 
 /// Attribute macro which marks a struct as being a data model and
 /// generates an implementation of [`DataObject`](butane_core::DataObject). This

butane_codegen/src/lib.rs

@@ -0,0 +1,26 @@
+# This project member only contains tests that built using `trybuild`.
+# These tests allow snapshotting of compiler errors and warnings to ensure that
+# incorrect usage of macros fails as expected, and provides useful error messages.
+# See the README.md in this directory for more information.
+[package]
+name = "trybuild_tests"
+edition.workspace = true
+license.workspace = true
+repository.workspace = true
+version.workspace = true
+rust-version.workspace = true
+autobenches = false
+autobins = false
+autoexamples = false
+
+[lib]
+doctest = false
+test = false
+
+[dependencies]
+
+[dev-dependencies]
+butane.workspace = true
+serde = { workspace = true, features = ["derive"] }
+serde_json.workspace = true
+trybuild = "1.0"