fix(derive-encode): Cumulative fixes

CHANGELOG.md

@@ -14,13 +14,28 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - `Family::get_or_create_owned` can access a metric in a labeled family. This
    method avoids the risk of runtime deadlocks at the expense of creating an
    owned type. See [PR 244].
- 
+
 [PR 244]: https://github.com/prometheus/client_rust/pull/244
 [PR 257]: https://github.com/prometheus/client_rust/pull/257
 
 ### Changed
 
 - `EncodeLabelSet::encode()` now accepts a mutable reference to its encoder parameter.
+- Emit better compilation error message when deriving marcos `EncodeLabelSet` and `EncodeLabelValue`.
+  See [PR 267].
+
+### Fixed
+
+- Fixed an issue where the derive marcos `EncodeLabelSet` and `EncodeLabelValue` didn't work
+  when the `struct` has generic parameters (like `'a`).
+  See [PR 265].
+
+- Fixed an issue where the derive macro `EncodeLabelSet` didn't work
+  when the `struct` has generic parameters (like `'a`).
+  See [PR 267].
+
+[PR 265]: https://github.com/prometheus/client_rust/pull/265
+[PR 267]: https://github.com/prometheus/client_rust/pull/266
 
 ## [0.23.1]
 

derive-encode/src/lib.rs

@@ -8,7 +8,7 @@
 
 use proc_macro::TokenStream;
 use proc_macro2::TokenStream as TokenStream2;
-use quote::quote;
+use quote::{quote, ToTokens};
 use syn::DeriveInput;
 
 /// Derive `prometheus_client::encoding::EncodeLabelSet`.
@@ -60,18 +60,41 @@ pub fn derive_encode_label_set(input: TokenStream) -> TokenStream {
                 })
                 .collect(),
             syn::Fields::Unnamed(_) => {
-                panic!("Can not derive Encode for struct with unnamed fields.")
+                return syn::Error::new_spanned(
+                    name,
+                    "Can not derive `EncodeLabelSet` for struct with unnamed fields.",
+                )
+                .to_compile_error()
+                .to_token_stream()
+                .into();
+            }
+            syn::Fields::Unit => {
+                return syn::Error::new_spanned(
+                    name,
+                    "Can not derive `EncodeLabelSet` for unit struct.",
+                )
+                .to_compile_error()
+                .to_token_stream()
+                .into();
             }
-            syn::Fields::Unit => panic!("Can not derive Encode for struct with unit field."),
         },
         syn::Data::Enum(syn::DataEnum { .. }) => {
-            panic!("Can not derive Encode for enum.")
+            return syn::Error::new_spanned(name, "Can not derive `EncodeLabelSet` for enum.")
+                .to_compile_error()
+                .to_token_stream()
+                .into();
+        }
+        syn::Data::Union(_) => {
+            return syn::Error::new_spanned(name, "Can not derive `EncodeLabelSet` for union.")
+                .to_compile_error()
+                .to_token_stream()
+                .into()
         }
-        syn::Data::Union(_) => panic!("Can not derive Encode for union."),
     };
 
+    let (impl_generics, ty_generics, where_clause) = ast.generics.split_for_impl();
     let gen = quote! {
-        impl ::prometheus_client::encoding::EncodeLabelSet for #name {
+        impl #impl_generics ::prometheus_client::encoding::EncodeLabelSet for #name #ty_generics #where_clause {
             fn encode(&self, encoder: &mut ::prometheus_client::encoding::LabelSetEncoder) -> ::core::result::Result<(), ::core::fmt::Error> {
                 use ::prometheus_client::encoding::EncodeLabel;
                 use ::prometheus_client::encoding::EncodeLabelKey;
@@ -95,7 +118,10 @@ pub fn derive_encode_label_value(input: TokenStream) -> TokenStream {
 
     let body = match ast.clone().data {
         syn::Data::Struct(_) => {
-            panic!("Can not derive EncodeLabel for struct.")
+            return syn::Error::new_spanned(name, "Can not derive `EncodeLabelValue` for struct.")
+                .to_compile_error()
+                .to_token_stream()
+                .into();
         }
         syn::Data::Enum(syn::DataEnum { variants, .. }) => {
             let match_arms: TokenStream2 = variants
@@ -114,7 +140,12 @@ pub fn derive_encode_label_value(input: TokenStream) -> TokenStream {
                 }
             }
         }
-        syn::Data::Union(_) => panic!("Can not derive Encode for union."),
+        syn::Data::Union(_) => {
+            return syn::Error::new_spanned(name, "Can not derive `EncodeLabelValue` for union.")
+                .to_compile_error()
+                .to_token_stream()
+                .into()
+        }
     };
 
     let gen = quote! {

derive-encode/tests/build/friendly-compilation-error-msg.rs

@@ -0,0 +1,50 @@
+use prometheus_client::encoding::EncodeLabelSet;
+use prometheus_client::encoding::EncodeLabelValue;
+
+mod A {
+    use super::*;
+
+    #[derive(Debug, Clone, PartialEq, Eq, Hash, EncodeLabelSet)]
+    struct Unnamed(String);
+
+    #[derive(Debug, Clone, PartialEq, Eq, Hash, EncodeLabelSet)]
+    struct Unit;
+
+    #[derive(Debug, Clone, PartialEq, Eq, Hash, EncodeLabelSet)]
+    enum Enum {
+        A,
+        B,
+    }
+
+    #[derive(Debug, Clone, PartialEq, Eq, Hash, EncodeLabelSet)]
+    enum DataEnum {
+        A,
+        B(String),
+    }
+
+    #[derive(Clone, Copy, EncodeLabelSet)]
+    #[repr(C)]
+    union Union {
+        a: u32,
+        b: u64,
+    }
+}
+
+mod B {
+    use super::*;
+
+    #[derive(Debug, Clone, PartialEq, Eq, Hash, EncodeLabelValue)]
+    struct Struct {
+        a: String,
+        b: String,
+    }
+
+    #[derive(Clone, Copy, EncodeLabelValue)]
+    #[repr(C)]
+    union Union {
+        a: u32,
+        b: u64,
+    }
+}
+
+fn main() {}

derive-encode/tests/build/friendly-compilation-error-msg.stderr

@@ -0,0 +1,41 @@
+error: Can not derive `EncodeLabelSet` for struct with unnamed fields.
+ --> tests/build/friendly-compilation-error-msg.rs:8:12
+  |
+8 |     struct Unnamed(String);
+  |            ^^^^^^^
+
+error: Can not derive `EncodeLabelSet` for unit struct.
+  --> tests/build/friendly-compilation-error-msg.rs:11:12
+   |
+11 |     struct Unit;
+   |            ^^^^
+
+error: Can not derive `EncodeLabelSet` for enum.
+  --> tests/build/friendly-compilation-error-msg.rs:14:10
+   |
+14 |     enum Enum {
+   |          ^^^^
+
+error: Can not derive `EncodeLabelSet` for enum.
+  --> tests/build/friendly-compilation-error-msg.rs:20:10
+   |
+20 |     enum DataEnum {
+   |          ^^^^^^^^
+
+error: Can not derive `EncodeLabelSet` for union.
+  --> tests/build/friendly-compilation-error-msg.rs:27:11
+   |
+27 |     union Union {
+   |           ^^^^^
+
+error: Can not derive `EncodeLabelValue` for struct.
+  --> tests/build/friendly-compilation-error-msg.rs:37:12
+   |
+37 |     struct Struct {
+   |            ^^^^^^
+
+error: Can not derive `EncodeLabelValue` for union.
+  --> tests/build/friendly-compilation-error-msg.rs:44:11
+   |
+44 |     union Union {
+   |           ^^^^^

derive-encode/tests/build/keep-impl-generics.rs

@@ -0,0 +1,18 @@
+use prometheus_client::encoding::EncodeLabelSet;
+use prometheus_client::encoding::EncodeLabelValue;
+
+#[derive(Debug, Clone, PartialEq, Eq, Hash, EncodeLabelValue)]
+enum CpuUsageLabelMode {
+    User,
+    System,
+    Irq,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Hash, EncodeLabelSet)]
+struct CpuUsageLabelSet<'a> { // <-- `'a` lifetime is used in the struct,
+                              // this should be preserved in the impl block
+    mode: CpuUsageLabelMode,
+    service: &'a str
+}
+
+fn main() {}

derive-encode/tests/lib.rs

@@ -209,5 +209,7 @@ fn flatten() {
 #[test]
 fn build() {
     let t = trybuild::TestCases::new();
-    t.pass("tests/build/redefine-prelude-symbols.rs")
+    t.pass("tests/build/redefine-prelude-symbols.rs");
+    t.pass("tests/build/keep-impl-generics.rs");
+    t.compile_fail("tests/build/friendly-compilation-error-msg.rs");
 }