attributes: don't record primitive types of the function arguments as…

… `fmt::Debug` (#1378)

## Motivation

The default behavior of `tracing::instrument` attribution will record
all of the function arguments as `fmt::Debug`, which is overwhelmed and
unnecessary for those primitive types, such as `bool`, `u8`, `i8`,
`u16`, `i16`, `u32`, `i32`, `u64`, `i64`, `usize`, and `isize`. Another
concerning reason is that we‘ll lose the type info of those primitive
types when record by a `Visitor`, while those type infos is essential to
some people. For example, I need to show my spans in Jaeger UI.

## Solution

Make the `tracing::instrument` records other function arguments as
`fmt::Debug ` while not for those primitive types.

However, I'm not good at naming. Maybe the `RecordType` enum and its
variant aren't a good name? I'd love to seek suggestions. Thanks.

tracing-attributes/src/lib.rs

@@ -96,9 +96,16 @@ use syn::{
 /// the function is called.
 ///
 /// Unless overriden, a span with `info` level will be generated.
-/// The generated span's name will be the name of the function. Any arguments
-/// to that function will be recorded as fields using [`fmt::Debug`]. To skip
-/// recording a function's or method's argument, pass the argument's name
+/// The generated span's name will be the name of the function.
+/// By default, all arguments to the function are included as fields on the
+/// span. Arguments that are `tracing` [primitive types] implementing the
+/// [`Value` trait] will be recorded as fields of that type. Types which do
+/// not implement `Value` will be recorded using [`std::fmt::Debug`].
+///
+/// [primitive types]: https://docs.rs/tracing/latest/tracing/field/trait.Value.html#foreign-impls
+/// [`Value` trait]: https://docs.rs/tracing/latest/tracing/field/trait.Value.html
+///
+/// To skip recording a function's or method's argument, pass the argument's name
 /// to the `skip` argument on the `#[instrument]` macro. For example,
 /// `skip` can be used when an argument to an instrumented function does
 /// not implement [`fmt::Debug`], or to exclude an argument with a verbose
@@ -400,12 +407,17 @@ fn gen_block(
     let span = (|| {
         // Pull out the arguments-to-be-skipped first, so we can filter results
         // below.
-        let param_names: Vec<(Ident, Ident)> = params
+        let param_names: Vec<(Ident, (Ident, RecordType))> = params
             .clone()
             .into_iter()
             .flat_map(|param| match param {
-                FnArg::Typed(PatType { pat, .. }) => param_names(*pat),
-                FnArg::Receiver(_) => Box::new(iter::once(Ident::new("self", param.span()))),
+                FnArg::Typed(PatType { pat, ty, .. }) => {
+                    param_names(*pat, RecordType::parse_from_ty(&*ty))
+                }
+                FnArg::Receiver(_) => Box::new(iter::once((
+                    Ident::new("self", param.span()),
+                    RecordType::Debug,
+                ))),
             })
             // Little dance with new (user-exposed) names and old (internal)
             // names of identifiers. That way, we could do the following
@@ -417,13 +429,13 @@ fn gen_block(
             //     async fn foo(&self, v: usize) {}
             // }
             // ```
-            .map(|x| {
+            .map(|(x, record_type)| {
                 // if we are inside a function generated by async-trait <=0.1.43, we need to
                 // take care to rewrite "_self" as "self" for 'user convenience'
                 if self_type.is_some() && x == "_self" {
-                    (Ident::new("self", x.span()), x)
+                    (Ident::new("self", x.span()), (x, record_type))
                 } else {
-                    (x.clone(), x)
+                    (x.clone(), (x, record_type))
                 }
             })
             .collect();
@@ -458,13 +470,16 @@ fn gen_block(
                     true
                 }
             })
-            .map(|(user_name, real_name)| quote!(#user_name = tracing::field::debug(&#real_name)))
+            .map(|(user_name, (real_name, record_type))| match record_type {
+                RecordType::Value => quote!(#user_name = #real_name),
+                RecordType::Debug => quote!(#user_name = tracing::field::debug(&#real_name)),
+            })
             .collect();
 
         // replace every use of a variable with its original name
         if let Some(Fields(ref mut fields)) = args.fields {
             let mut replacer = IdentAndTypesRenamer {
-                idents: param_names,
+                idents: param_names.into_iter().map(|(a, (b, _))| (a, b)).collect(),
                 types: Vec::new(),
             };
 
@@ -853,20 +868,93 @@ impl Parse for Level {
     }
 }
 
-fn param_names(pat: Pat) -> Box<dyn Iterator<Item = Ident>> {
+/// Indicates whether a field should be recorded as `Value` or `Debug`.
+enum RecordType {
+    /// The field should be recorded using its `Value` implementation.
+    Value,
+    /// The field should be recorded using `tracing::field::debug()`.
+    Debug,
+}
+
+impl RecordType {
+    /// Array of primitive types which should be recorded as [RecordType::Value].
+    const TYPES_FOR_VALUE: [&'static str; 23] = [
+        "bool",
+        "str",
+        "u8",
+        "i8",
+        "u16",
+        "i16",
+        "u32",
+        "i32",
+        "u64",
+        "i64",
+        "usize",
+        "isize",
+        "NonZeroU8",
+        "NonZeroI8",
+        "NonZeroU16",
+        "NonZeroI16",
+        "NonZeroU32",
+        "NonZeroI32",
+        "NonZeroU64",
+        "NonZeroI64",
+        "NonZeroUsize",
+        "NonZeroIsize",
+        "Wrapping",
+    ];
+
+    /// Parse `RecordType` from [syn::Type] by looking up
+    /// the [RecordType::TYPES_FOR_VALUE] array.
+    fn parse_from_ty(ty: &syn::Type) -> Self {
+        match ty {
+            syn::Type::Path(syn::TypePath { path, .. })
+                if path
+                    .segments
+                    .iter()
+                    .last()
+                    .map(|path_segment| {
+                        let ident = path_segment.ident.to_string();
+                        Self::TYPES_FOR_VALUE.iter().any(|&t| t == ident)
+                    })
+                    .unwrap_or(false) =>
+            {
+                RecordType::Value
+            }
+            syn::Type::Reference(syn::TypeReference { elem, .. }) => {
+                RecordType::parse_from_ty(&*elem)
+            }
+            _ => RecordType::Debug,
+        }
+    }
+}
+
+fn param_names(pat: Pat, record_type: RecordType) -> Box<dyn Iterator<Item = (Ident, RecordType)>> {
     match pat {
-        Pat::Ident(PatIdent { ident, .. }) => Box::new(iter::once(ident)),
-        Pat::Reference(PatReference { pat, .. }) => param_names(*pat),
+        Pat::Ident(PatIdent { ident, .. }) => Box::new(iter::once((ident, record_type))),
+        Pat::Reference(PatReference { pat, .. }) => param_names(*pat, record_type),
+        // We can't get the concrete type of fields in the struct/tuple
+        // patterns by using `syn`. e.g. `fn foo(Foo { x, y }: Foo) {}`.
+        // Therefore, the struct/tuple patterns in the arguments will just
+        // always be recorded as `RecordType::Debug`.
         Pat::Struct(PatStruct { fields, .. }) => Box::new(
             fields
                 .into_iter()
-                .flat_map(|FieldPat { pat, .. }| param_names(*pat)),
+                .flat_map(|FieldPat { pat, .. }| param_names(*pat, RecordType::Debug)),
+        ),
+        Pat::Tuple(PatTuple { elems, .. }) => Box::new(
+            elems
+                .into_iter()
+                .flat_map(|p| param_names(p, RecordType::Debug)),
         ),
-        Pat::Tuple(PatTuple { elems, .. }) => Box::new(elems.into_iter().flat_map(param_names)),
         Pat::TupleStruct(PatTupleStruct {
             pat: PatTuple { elems, .. },
             ..
-        }) => Box::new(elems.into_iter().flat_map(param_names)),
+        }) => Box::new(
+            elems
+                .into_iter()
+                .flat_map(|p| param_names(p, RecordType::Debug)),
+        ),
 
         // The above *should* cover all cases of irrefutable patterns,
         // but we purposefully don't do any funny business here

tracing-attributes/tests/async_fn.rs

@@ -182,7 +182,7 @@ fn async_fn_with_async_trait_and_fields_expressions() {
         .new_span(
             span.clone().with_field(
                 field::mock("_v")
-                    .with_value(&tracing::field::debug(5))
+                    .with_value(&5usize)
                     .and(field::mock("test").with_value(&tracing::field::debug(10)))
                     .and(field::mock("val").with_value(&42u64))
                     .and(field::mock("val2").with_value(&42u64)),

tracing-attributes/tests/destructuring.rs

@@ -74,7 +74,7 @@ fn destructure_refs() {
     let (collector, handle) = collector::mock()
         .new_span(
             span.clone()
-                .with_field(field::mock("arg1").with_value(&format_args!("1")).only()),
+                .with_field(field::mock("arg1").with_value(&1usize).only()),
         )
         .enter(span.clone())
         .exit(span.clone())

tracing-attributes/tests/err.rs

@@ -152,7 +152,7 @@ fn impl_trait_return_type() {
     let (collector, handle) = collector::mock()
         .new_span(
             span.clone()
-                .with_field(field::mock("x").with_value(&format_args!("10")).only()),
+                .with_field(field::mock("x").with_value(&10usize).only()),
         )
         .enter(span.clone())
         .exit(span.clone())

tracing-attributes/tests/fields.rs

@@ -61,7 +61,7 @@ fn fields() {
 fn expr_field() {
     let span = span::mock().with_field(
         mock("s")
-            .with_value(&tracing::field::debug("hello world"))
+            .with_value(&"hello world")
             .and(mock("len").with_value(&"hello world".len()))
             .only(),
     );
@@ -74,7 +74,7 @@ fn expr_field() {
 fn two_expr_fields() {
     let span = span::mock().with_field(
         mock("s")
-            .with_value(&tracing::field::debug("hello world"))
+            .with_value(&"hello world")
             .and(mock("s.len").with_value(&"hello world".len()))
             .and(mock("s.is_empty").with_value(&false))
             .only(),
@@ -120,7 +120,7 @@ fn parameters_with_fields() {
     let span = span::mock().with_field(
         mock("foo")
             .with_value(&"bar")
-            .and(mock("param").with_value(&format_args!("1")))
+            .and(mock("param").with_value(&1u32))
             .only(),
     );
     run_test(span, || {

tracing-attributes/tests/instrument.rs

@@ -59,8 +59,8 @@ fn fields() {
         .new_span(
             span.clone().with_field(
                 field::mock("arg1")
-                    .with_value(&format_args!("2"))
-                    .and(field::mock("arg2").with_value(&format_args!("false")))
+                    .with_value(&2usize)
+                    .and(field::mock("arg2").with_value(&false))
                     .only(),
             ),
         )
@@ -70,8 +70,8 @@ fn fields() {
         .new_span(
             span2.clone().with_field(
                 field::mock("arg1")
-                    .with_value(&format_args!("3"))
-                    .and(field::mock("arg2").with_value(&format_args!("true")))
+                    .with_value(&3usize)
+                    .and(field::mock("arg2").with_value(&true))
                     .only(),
             ),
         )
@@ -108,15 +108,15 @@ fn skip() {
     let (collector, handle) = collector::mock()
         .new_span(
             span.clone()
-                .with_field(field::mock("arg1").with_value(&format_args!("2")).only()),
+                .with_field(field::mock("arg1").with_value(&2usize).only()),
         )
         .enter(span.clone())
         .exit(span.clone())
         .drop_span(span)
         .new_span(
             span2
                 .clone()
-                .with_field(field::mock("arg1").with_value(&format_args!("3")).only()),
+                .with_field(field::mock("arg1").with_value(&3usize).only()),
         )
         .enter(span2.clone())
         .exit(span2.clone())
@@ -184,7 +184,7 @@ fn methods() {
             span.clone().with_field(
                 field::mock("self")
                     .with_value(&format_args!("Foo"))
-                    .and(field::mock("arg1").with_value(&format_args!("42"))),
+                    .and(field::mock("arg1").with_value(&42usize)),
             ),
         )
         .enter(span.clone())
@@ -213,7 +213,7 @@ fn impl_trait_return_type() {
     let (collector, handle) = collector::mock()
         .new_span(
             span.clone()
-                .with_field(field::mock("x").with_value(&format_args!("10")).only()),
+                .with_field(field::mock("x").with_value(&10usize).only()),
         )
         .enter(span.clone())
         .exit(span.clone())