From 0fb498f1c475691d0a5b92ef606cb9efee8671ae Mon Sep 17 00:00:00 2001
From: michele <michele.damico@gmail.com>
Date: Sat, 27 Nov 2021 15:34:08 +0100
Subject: [PATCH] #119 Implemented error handling in for generics

---
 src/error.rs                      | 88 ++++++++++++++++++++++++++++++-
 tests/fixture/mod.rs              | 30 +++++++++++
 tests/resources/fixture/errors.rs | 14 ++++-
 3 files changed, 129 insertions(+), 3 deletions(-)

diff --git a/src/error.rs b/src/error.rs
index 09e05a2..8c0db23 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -2,8 +2,8 @@
 use std::collections::HashMap;
 
 use proc_macro2::TokenStream;
-use syn::spanned::Spanned;
-use syn::ItemFn;
+use syn::{spanned::Spanned, visit::Visit};
+use syn::{visit, ItemFn};
 
 use crate::parse::{
     fixture::FixtureInfo,
@@ -26,6 +26,7 @@ pub(crate) fn fixture(test: &ItemFn, info: &FixtureInfo) -> TokenStream {
     missed_arguments(test, info.data.items.iter())
         .chain(duplicate_arguments(info.data.items.iter()))
         .chain(async_once(test, &info))
+        .chain(generics_once(test, &info))
         .map(|e| e.to_compile_error())
         .collect()
 }
@@ -40,6 +41,44 @@ fn async_once<'a>(test: &'a ItemFn, info: &FixtureInfo) -> Errors<'a> {
     }
 }
 
+#[derive(Default)]
+struct SearchImpl(bool);
+
+impl<'ast> Visit<'ast> for SearchImpl {
+    fn visit_type(&mut self, i: &'ast syn::Type) {
+        if self.0 {
+            return;
+        }
+        match i {
+            syn::Type::ImplTrait(_) => self.0 = true,
+            _ => {}
+        }
+        visit::visit_type(self, i);
+    }
+}
+
+impl SearchImpl {
+    fn function_has_some_impl(f: &ItemFn) -> bool {
+        let mut s = SearchImpl::default();
+        visit::visit_item_fn(&mut s, f);
+        s.0
+    }
+}
+
+fn has_some_generics(test: &ItemFn) -> bool {
+    test.sig.generics.params.len() > 0 || SearchImpl::function_has_some_impl(test)
+}
+
+fn generics_once<'a>(test: &'a ItemFn, info: &FixtureInfo) -> Errors<'a> {
+    match (has_some_generics(test), info.attributes.get_once()) {
+        (true, Some(once)) => Box::new(std::iter::once(syn::Error::new(
+            once.span(),
+            "Cannot apply #[once] on generic fixture.",
+        ))),
+        _ => Box::new(std::iter::empty()),
+    }
+}
+
 #[derive(Debug, Default)]
 pub(crate) struct ErrorsVec(Vec<syn::Error>);
 
@@ -189,3 +228,48 @@ fn case_args_without_cases(params: &RsTestData) -> Errors {
     }
     Box::new(std::iter::empty())
 }
+
+#[cfg(test)]
+mod test {
+    use crate::test::{assert_eq, *};
+    use rstest_test::assert_in;
+
+    use super::*;
+
+    #[rstest]
+    #[case::generics("fn f<G: SomeTrait>(){}")]
+    #[case::const_generics("fn f<const N: usize>(){}")]
+    #[case::lifetimes("fn f<'a>(){}")]
+    #[case::use_impl_in_answer("fn f() -> impl Iterator<Item=u32>{}")]
+    #[case::use_impl_in_argumets("fn f(it: impl Iterator<Item=u32>){}")]
+    #[should_panic]
+    #[case::sanity_check_with_no_generics("fn f() {}")]
+    fn generics_once_should_return_error(#[case] f: &str) {
+        let f: ItemFn = f.ast();
+        let info = FixtureInfo::default().with_once();
+
+        let errors = generics_once(&f, &info);
+
+        let out = errors
+            .map(|e| format!("{:?}", e))
+            .collect::<Vec<_>>()
+            .join("-----------------------\n");
+
+        assert_in!(out, "Cannot apply #[once] on generic fixture.");
+    }
+
+    #[rstest]
+    #[case::generics("fn f<G: SomeTrait>(){}")]
+    #[case::const_generics("fn f<const N: usize>(){}")]
+    #[case::lifetimes("fn f<'a>(){}")]
+    #[case::use_impl_in_answer("fn f() -> impl Iterator<Item=u32>{}")]
+    #[case::use_impl_in_argumets("fn f(it: impl Iterator<Item=u32>){}")]
+    fn generics_once_should_not_return_if_no_once(#[case] f: &str) {
+        let f: ItemFn = f.ast();
+        let info = FixtureInfo::default();
+
+        let errors = generics_once(&f, &info);
+
+        assert_eq!(0, errors.count());
+    }
+}
diff --git a/tests/fixture/mod.rs b/tests/fixture/mod.rs
index 169c7f0..9521f1a 100644
--- a/tests/fixture/mod.rs
+++ b/tests/fixture/mod.rs
@@ -306,5 +306,35 @@ mod should {
             )
             .unindent()
         );
+
+        assert_in!(
+            output.stderr.str(),
+            format!(
+                r#"
+                error: Cannot apply #[once] on generic fixture.
+                  --> {}/src/lib.rs:43:3
+                   |
+                43 | #[once]
+                   |   ^^^^
+                "#,
+                name
+            )
+            .unindent()
+        );
+
+        assert_in!(
+            output.stderr.str(),
+            format!(
+                r#"
+                error: Cannot apply #[once] on generic fixture.
+                  --> {}/src/lib.rs:49:3
+                   |
+                49 | #[once]
+                   |   ^^^^
+                "#,
+                name
+            )
+            .unindent()
+        );
     }
 }
diff --git a/tests/resources/fixture/errors.rs b/tests/resources/fixture/errors.rs
index d465d9e..d185104 100644
--- a/tests/resources/fixture/errors.rs
+++ b/tests/resources/fixture/errors.rs
@@ -37,4 +37,16 @@ fn error_inject_a_fixture_more_than_once(f: String) {
 #[fixture]
 #[once]
 async fn error_async_once_fixture() {
-}
\ No newline at end of file
+}
+
+#[fixture]
+#[once]
+fn error_generics_once_fixture<T: std::fmt::Debug>() -> T {
+    42
+}
+
+#[fixture]
+#[once]
+fn error_generics_once_fixture() -> impl Iterator<Item: u32> {
+    std::iter::once(42)
+}