warning: fields `name` and `location` are never read
  --> core/src/trace/span.rs:36:5
   |
35 | pub struct Callsite {
   |            -------- fields in this struct
36 |     name: &'static str,
   |     ^^^^
37 |     location: Location,
   |     ^^^^^^^^

warning: fields `location` and `level` are never read
  --> core/src/logger.rs:34:5
   |
33 | pub struct Callsite {
   |            -------- fields in this struct
34 |     location: Location,
   |     ^^^^^^^^
35 |     level: Level
   |     ^^^^^

warning: variant `None` is never constructed
  --> core/src/core/engine.rs:35:5
   |
34 | pub enum Engine {
   |          ------ variant in this enum
35 |     None,
   |     ^^^^
   |
   = note: `#[warn(dead_code)]` on by default

warning: unused variable: `fields`
  --> core/src/core/engine.rs:72:79
   |
72 |     fn log(&self, callsite: &'static crate::logger::Callsite, msg: Arguments, fields: &FieldSet) {
   |                                                                               ^^^^^^ help: if this is intentional, prefix it with an underscore: `_fields`

warning: unused variable: `msg`
  --> core/src/core/engine.rs:72:63
   |
72 |     fn log(&self, callsite: &'static crate::logger::Callsite, msg: Arguments, fields: &FieldSet) {
   |                                                               ^^^ help: if this is intentional, prefix it with an underscore: `_msg`

warning: unused variable: `callsite`
  --> core/src/core/engine.rs:72:19
   |
72 |     fn log(&self, callsite: &'static crate::logger::Callsite, msg: Arguments, fields: &FieldSet) {
   |                   ^^^^^^^^ help: if this is intentional, prefix it with an underscore: `_callsite`

warning: unused variable: `id`
  --> core/src/core/engine.rs:66:25
   |
66 |     fn span_exit(&self, id: NonZeroU32) {
   |                         ^^ help: if this is intentional, prefix it with an underscore: `_id`

warning: unused variable: `fields`
  --> core/src/core/engine.rs:62:43
   |
62 |     fn span_record(&self, id: NonZeroU32, fields: &FieldSet) {
   |                                           ^^^^^^ help: if this is intentional, prefix it with an underscore: `_fields`

warning: unused variable: `id`
  --> core/src/core/engine.rs:62:27
   |
62 |     fn span_record(&self, id: NonZeroU32, fields: &FieldSet) {
   |                           ^^ help: if this is intentional, prefix it with an underscore: `_id`

warning: unused variable: `id`
  --> core/src/core/engine.rs:58:26
   |
58 |     fn span_enter(&self, id: NonZeroU32) {
   |                          ^^ help: if this is intentional, prefix it with an underscore: `_id`

warning: unused variable: `fields`
  --> core/src/core/engine.rs:54:49
   |
54 |     fn span_create(&self, callsite: NonZeroU32, fields: &FieldSet) -> NonZeroU32 {
   |                                                 ^^^^^^ help: if this is intentional, prefix it with an underscore: `_fields`

warning: unused variable: `callsite`
  --> core/src/core/engine.rs:54:27
   |
54 |     fn span_create(&self, callsite: NonZeroU32, fields: &FieldSet) -> NonZeroU32 {
   |                           ^^^^^^^^ help: if this is intentional, prefix it with an underscore: `_callsite`

warning: unused variable: `callsite`
  --> core/src/core/engine.rs:50:33
   |
50 |     fn register_callsite(&self, callsite: &'static Callsite) -> NonZeroU32 {
   |                                 ^^^^^^^^ help: if this is intentional, prefix it with an underscore: `_callsite`

warning: unused variable: `fields`
  --> core/src/core/engine.rs:44:68
   |
44 |     fn section_record(&self, id: NonZeroU32, start: u64, end: u64, fields: &FieldSet) {
   |                                                                    ^^^^^^ help: if this is intentional, prefix it with an underscore: `_fields`

warning: unused variable: `end`
  --> core/src/core/engine.rs:44:58
   |
44 |     fn section_record(&self, id: NonZeroU32, start: u64, end: u64, fields: &FieldSet) {
   |                                                          ^^^ help: if this is intentional, prefix it with an underscore: `_end`

warning: unused variable: `start`
  --> core/src/core/engine.rs:44:46
   |
44 |     fn section_record(&self, id: NonZeroU32, start: u64, end: u64, fields: &FieldSet) {
   |                                              ^^^^^ help: if this is intentional, prefix it with an underscore: `_start`

warning: unused variable: `id`
  --> core/src/core/engine.rs:44:30
   |
44 |     fn section_record(&self, id: NonZeroU32, start: u64, end: u64, fields: &FieldSet) {
   |                              ^^ help: if this is intentional, prefix it with an underscore: `_id`

warning: unused variable: `section`
  --> core/src/core/engine.rs:40:32
   |
40 |     fn section_register(&self, section: &'static crate::profiler::section::Section) -> NonZeroU32 {
   |                                ^^^^^^^ help: if this is intentional, prefix it with an underscore: `_section`
   |
   = note: `#[warn(unused_variables)]` on by default