Merge pull request #4054 from weiznich/fix/auto_type_lifetimes

Fix lifetimes with `#[auto_type]`

Author: weiznich

diesel_compile_tests/tests/fail/auto_type_life_times.rs

@@ -0,0 +1,23 @@
+use diesel::dsl::*;
+use diesel::prelude::*;
+
+diesel::table! {
+    users {
+        id -> Integer,
+        name -> Text,
+    }
+}
+
+#[auto_type]
+fn with_lifetime(name: &'_ str) -> _ {
+    users::table.filter(users::name.eq(name))
+}
+
+#[auto_type]
+fn with_lifetime2(name: &str) -> _ {
+    users::table.filter(users::name.eq(name))
+}
+
+fn main() {
+    println!("Hello, world!");
+}

diesel_compile_tests/tests/fail/auto_type_life_times.stderr

@@ -0,0 +1,49 @@
+error: `#[auto_type]` requires named lifetimes
+  --> tests/fail/auto_type_life_times.rs:12:25
+   |
+12 | fn with_lifetime(name: &'_ str) -> _ {
+   |                         ^^
+
+error: `#[auto_type]` requires named lifetimes
+  --> tests/fail/auto_type_life_times.rs:17:25
+   |
+17 | fn with_lifetime2(name: &str) -> _ {
+   |                         ^^^^
+
+error[E0106]: missing lifetime specifier
+  --> tests/fail/auto_type_life_times.rs:12:25
+   |
+12 | fn with_lifetime(name: &'_ str) -> _ {
+   |                         ^^ expected named lifetime parameter
+   |
+help: consider introducing a named lifetime parameter
+   |
+12 | fn with_lifetime<'a>(name: &'a str) -> _ {
+   |                 ++++        ~~
+
+error[E0106]: missing lifetime specifier
+  --> tests/fail/auto_type_life_times.rs:17:25
+   |
+17 | fn with_lifetime2(name: &str) -> _ {
+   |                         ^ expected named lifetime parameter
+   |
+help: consider introducing a named lifetime parameter
+   |
+17 | fn with_lifetime2<'a>(name: &'a str) -> _ {
+   |                  ++++        ++
+
+error: lifetime may not live long enough
+  --> tests/fail/auto_type_life_times.rs:13:5
+   |
+12 | fn with_lifetime(name: &'_ str) -> _ {
+   |                        - let's call the lifetime of this reference `'1`
+13 |     users::table.filter(users::name.eq(name))
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ returning this value requires that `'1` must outlive `'static`
+
+error: lifetime may not live long enough
+  --> tests/fail/auto_type_life_times.rs:18:5
+   |
+17 | fn with_lifetime2(name: &str) -> _ {
+   |                         - let's call the lifetime of this reference `'1`
+18 |     users::table.filter(users::name.eq(name))
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ returning this value requires that `'1` must outlive `'static`

diesel_derives/tests/auto_type.rs

@@ -355,6 +355,24 @@ fn test_normal_functions() -> _ {
     ))
 }
 
+#[auto_type]
+fn with_lifetime<'a>(name: &'a str) -> _ {
+    users::table.filter(users::name.eq(name))
+}
+
+#[auto_type]
+fn with_type_generics<'a, T>(name: &'a T) -> _
+where
+    &'a T: diesel::expression::AsExpression<diesel::sql_types::Text>,
+{
+    users::name.eq(name)
+}
+
+#[auto_type]
+fn with_const_generics<const N: i32>() -> _ {
+    users::id.eq(N)
+}
+
 // #[auto_type]
 // fn test_sql_fragment() -> _ {
 //     sql("foo")

dsl_auto_type/Cargo.toml

@@ -15,7 +15,7 @@ either = "1"
 heck = "0.5"
 proc-macro2 = "1"
 quote = "1"
-syn = { version = "2", features = ["extra-traits", "full", "derive", "parsing"] }
+syn = { version = "2", features = ["extra-traits", "full", "derive", "parsing", "visit"] }
 
 [dev-dependencies]
 diesel = { path = "../diesel" }

dsl_auto_type/src/auto_type/expression_type_inference.rs

@@ -73,10 +73,12 @@ impl TypeInferrer<'_> {
             Err(e) => self.register_error(e, expr.span()),
         }
     }
+
     fn register_error(&self, error: syn::Error, infer_type_span: Span) -> syn::Type {
         self.errors.borrow_mut().push(Rc::new(error));
         parse_quote_spanned!(infer_type_span=> _)
     }
+
     fn try_infer_expression_type(
         &self,
         expr: &syn::Expr,

dsl_auto_type/src/auto_type/local_variables_map.rs

@@ -116,6 +116,16 @@ impl<'a, 'p> LocalVariablesMap<'a, 'p> {
         Ok(())
     }
 
+    pub(crate) fn process_const_generic(&mut self, const_generic: &'a syn::ConstParam) {
+        self.inner.map.insert(
+            &const_generic.ident,
+            LetStatementInferredType {
+                type_: const_generic.ty.clone(),
+                errors: Vec::new(),
+            },
+        );
+    }
+
     /// Finishes a block inference for this map.
     /// It may be initialized with `pat`s before (such as function parameters),
     /// then this function is used to infer the type of the last expression in the block.

dsl_auto_type/src/auto_type/mod.rs

@@ -1,6 +1,7 @@
 mod case;
 pub mod expression_type_inference;
 mod local_variables_map;
+mod referenced_generics;
 mod settings_builder;
 
 use {
@@ -134,6 +135,9 @@ pub(crate) fn auto_type_impl(
                     parent: None,
                 },
             };
+            for const_generic in input_function.sig.generics.const_params() {
+                local_variables_map.process_const_generic(const_generic);
+            }
             for function_param in &input_function.sig.inputs {
                 if let syn::FnArg::Typed(syn::PatType { pat, ty, .. }) = function_param {
                     match local_variables_map.process_pat(pat, Some(ty), None) {
@@ -165,11 +169,19 @@ pub(crate) fn auto_type_impl(
 
     let type_alias = match type_alias {
         Some(type_alias) => {
+            // We're generating a type alias so we need to extract the necessary lifetimes and
+            // generic type parameters for that type alias
+            let type_alias_generics = referenced_generics::extract_referenced_generics(
+                &return_type,
+                &input_function.sig.generics,
+                &mut errors,
+            );
+
             let vis = &input_function.vis;
-            input_function.sig.output = parse_quote!(-> #type_alias);
+            input_function.sig.output = parse_quote!(-> #type_alias #type_alias_generics);
             quote! {
                 #[allow(non_camel_case_types)]
-                #vis type #type_alias = #return_type;
+                #vis type #type_alias #type_alias_generics = #return_type;
             }
         }
         None => {
@@ -180,12 +192,13 @@ pub(crate) fn auto_type_impl(
 
     let mut res = quote! {
         #type_alias
+        #[allow(clippy::needless_lifetimes)]
         #input_function
     };
 
     for error in errors {
         // Extracting from the `Rc` only if it's the last reference is an elegant way to
-        // deduplicate errors For this to work it is necessary that the rest of
+        // deduplicate errors. For this to work it is necessary that the rest of
         // the errors (those from the local variables map that weren't used) are
         // dropped before, which is the case here, and that we are iterating on the
         // errors in an owned manner.

dsl_auto_type/src/auto_type/referenced_generics.rs

@@ -0,0 +1,109 @@
+use std::rc::Rc;
+use syn::parse_quote;
+use syn::visit::{self, Visit};
+use syn::{Ident, Lifetime};
+
+pub(crate) fn extract_referenced_generics(
+    ty: &syn::Type,
+    generics: &syn::Generics,
+    errors: &mut Vec<Rc<syn::Error>>,
+) -> syn::Generics {
+    struct Visitor<'g, 'errs> {
+        lifetimes: Vec<(&'g Lifetime, bool)>,
+        type_parameters: Vec<(&'g Ident, bool)>,
+        errors: &'errs mut Vec<Rc<syn::Error>>,
+    }
+
+    let mut visitor = Visitor {
+        lifetimes: generics
+            .lifetimes()
+            .map(|lt| (&lt.lifetime, false))
+            .collect(),
+        type_parameters: generics
+            .type_params()
+            .map(|tp| (&tp.ident, false))
+            .collect(),
+        errors,
+    };
+    visitor.lifetimes.sort_unstable();
+    visitor.type_parameters.sort_unstable();
+
+    impl<'ast> Visit<'ast> for Visitor<'_, '_> {
+        fn visit_lifetime(&mut self, lifetime: &'ast Lifetime) {
+            if lifetime.ident == "_" {
+                self.errors.push(Rc::new(syn::Error::new_spanned(
+                    lifetime,
+                    "`#[auto_type]` requires named lifetimes",
+                )));
+            } else if lifetime.ident != "static" {
+                if let Ok(lifetime_idx) = self
+                    .lifetimes
+                    .binary_search_by_key(&lifetime, |(lt, _)| *lt)
+                {
+                    self.lifetimes[lifetime_idx].1 = true;
+                }
+            }
+            visit::visit_lifetime(self, lifetime)
+        }
+
+        fn visit_type_reference(&mut self, reference: &'ast syn::TypeReference) {
+            if reference.lifetime.is_none() {
+                self.errors.push(Rc::new(syn::Error::new_spanned(
+                    reference,
+                    "`#[auto_type]` requires named lifetimes",
+                )));
+            }
+            visit::visit_type_reference(self, reference)
+        }
+
+        fn visit_type_path(&mut self, type_path: &'ast syn::TypePath) {
+            if let Some(path_ident) = type_path.path.get_ident() {
+                if let Ok(type_param_idx) = self
+                    .type_parameters
+                    .binary_search_by_key(&path_ident, |tp| tp.0)
+                {
+                    self.type_parameters[type_param_idx].1 = true;
+                }
+            }
+            visit::visit_type_path(self, type_path)
+        }
+    }
+
+    visitor.visit_type(ty);
+
+    let generic_params: syn::punctuated::Punctuated<syn::GenericParam, _> = generics
+        .params
+        .iter()
+        .filter_map(|param| match param {
+            syn::GenericParam::Lifetime(lt)
+                if visitor
+                    .lifetimes
+                    .binary_search(&(&lt.lifetime, true))
+                    .is_ok() =>
+            {
+                let lt = &lt.lifetime;
+                Some(parse_quote!(#lt))
+            }
+            syn::GenericParam::Type(tp)
+                if visitor
+                    .type_parameters
+                    .binary_search(&(&tp.ident, true))
+                    .is_ok() =>
+            {
+                let ident = &tp.ident;
+                Some(parse_quote!(#ident))
+            }
+            _ => None::<syn::GenericParam>,
+        })
+        .collect();
+
+    // We need to not set the lt_token and gt_token if `params` is empty to get
+    // a reasonable error message for the case that there is no lifetime specifier
+    // but we need one
+    syn::Generics {
+        lt_token: (!generic_params.is_empty()).then(Default::default),
+        gt_token: (!generic_params.is_empty()).then(Default::default),
+        params: generic_params,
+        where_clause: None,
+    }
+}