Test Coverage: cannot find uncovered lines and regions

[Nugine]

https://github.com/Nugine/scoped-writer

https://github.com/Nugine/scoped-writer/blob/v0.2.0/src/lib.rs (Only 77 LoC)

git clone https://github.com/Nugine/scoped-writer
cd scoped-writer
git checkout v0.2.0

cargo llvm-cov --html --open

When I click next uncovered line (L) or next uncovered region (R), there is no reaction. I don't know what is uncovered.

Related

• https://github.com/taiki-e/cargo-llvm-cov
• Incorrect Rust region coverage? taiki-e/cargo-llvm-cov#324
• can't find missing line taiki-e/cargo-llvm-cov#380

[Nugine]

git clone https://github.com/Nugine/scoped-writer
cd scoped-writer
git checkout v0.2.0

cargo tarpaulin

2025-02-24T11:18:07.805680Z  INFO cargo_tarpaulin::report: Coverage Results:
|| Uncovered Lines:
|| Tested/Total Lines:
|| src/lib.rs: 21/21
|| 
100.00% coverage, 21/21 lines covered

[Zalathar]

Hmm, I'm curious to see what shows up in the --text and --json reports as opposed to the HTML report.

Would you be able to run those, and post or link them here?

[Zalathar]

(The fact that the HTML report can't jump to uncovered lines/regions is arguably an LLVM bug, but it's quite possible that we're emitting something that weird that is causing LLVM's tools to behave strangely, so we would want to fix that on our end if possible anyway.)

[Nugine]

Here are --text and --json reports

git clone https://github.com/Nugine/scoped-writer
cd scoped-writer
git checkout v0.2.0

cargo llvm-cov --text

    1|       |#![allow(unsafe_code)]
    2|       |#![deny(clippy::all, clippy::pedantic, clippy::cargo)]
    3|       |
    4|       |use std::cell::RefCell;
    5|       |use std::io;
    6|       |use std::ptr;
    7|       |
    8|       |type SlotType = *mut dyn io::Write;
    9|       |
   10|       |thread_local! {
   11|       |    static SLOT: RefCell<*mut SlotType> = const { RefCell::new(ptr::null_mut()) };
   12|       |}
   13|       |
   14|       |struct SlotGuard(*mut SlotType);
   15|       |
   16|       |impl SlotGuard {
   17|       |    #[must_use]
   18|      5|    fn new(cur: *mut SlotType) -> Self {
   19|      5|        let prev = SLOT.with(|slot| slot.replace(cur));
   20|      5|        SlotGuard(prev)
   21|      5|    }
   22|       |}
   23|       |
   24|       |impl Drop for SlotGuard {
   25|      5|    fn drop(&mut self) {
   26|      5|        SLOT.with(|slot| *slot.borrow_mut() = self.0);
   27|      5|    }
   28|       |}
   29|       |
   30|       |/// Sets the global writer for the duration of the closure in current thread.
   31|      5|pub fn scoped<R>(mut w: &mut dyn io::Write, f: impl FnOnce() -> R) -> R {
   32|      5|    let _guard = SlotGuard::new(ptr::addr_of_mut!(w).cast());
   33|      5|    f()
   34|      5|}
   35|       |
   36|       |/// Executes a closure with the global writer, skips if the writer is not set.
   37|       |///
   38|       |/// Reentrancy is not allowed.
   39|       |///
   40|       |/// # Panics
   41|       |/// Panics if this function is called recursively
   42|     12|pub fn with<R>(f: impl FnOnce(&mut dyn io::Write) -> R) -> Option<R> {
   43|     12|    SLOT.with(|slot| {
   44|     12|        let Ok(cur) = slot.try_borrow_mut() else {
                             ^11
   45|      1|            panic!("Reentrancy is not allowed")
   46|       |        };
   47|     11|        let p = cur.cast::<&mut dyn io::Write>();
   48|     11|        if p.is_null() {
   49|      4|            None
   50|       |        } else {
   51|      7|            Some(f(unsafe { &mut **p }))
   52|       |        }
   53|     12|    })
                  ^11
   54|     12|}
   55|       |
   56|       |/// [`writeln!`] to the global writer.
   57|       |#[macro_export]
   58|       |macro_rules! g {
   59|       |    () => {{
   60|      1|        $crate::with(|w|writeln!(w).unwrap());
   61|       |    }};
   62|       |    ($fmt:literal $($arg:tt)*) => {{
   63|      4|        $crate::with(|w|writeln!(w, $fmt $($arg)*).unwrap());
   64|       |    }};
   65|       |}
   66|       |
   67|       |/// Writes lines to the global writer.
   68|      1|pub fn g<L>(lines: impl AsRef<[L]>)
   69|      1|where
   70|      1|    L: AsRef<str>,
   71|      1|{
   72|      1|    with(|w| {
   73|      3|        for line in lines.as_ref() {
                                  ^1
   74|      3|            writeln!(w, "{}", line.as_ref()).unwrap();
   75|      3|        }
   76|      1|    });
   77|      1|}

cargo llvm-cov --json

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$ rustc -v --version
rustc 1.85.0 (4d91de4e4 2025-02-17)
binary: rustc
commit-hash: 4d91de4e48198da2e33413efdcd9cd2cc0c46688
commit-date: 2025-02-17
host: x86_64-unknown-linux-gnu
release: 1.85.0
LLVM version: 19.1.7

[Zalathar]

Ah, I think what's happening is that the closures in g! are being instantiated at multiple sites in the test file.

Some of those instantiations are unused, but others are used, and the used ones appear to have made the unused ones invisible, even though they are still counted in the totals.

Does running cargo llvm-cov with --show-instantiations make the uncovered regions visible in the report?

[Nugine]

cargo llvm-cov --show-instantiations --text

    1|       |#![allow(unsafe_code)]
    2|       |#![deny(clippy::all, clippy::pedantic, clippy::cargo)]
    3|       |
    4|       |use std::cell::RefCell;
    5|       |use std::io;
    6|       |use std::ptr;
    7|       |
    8|       |type SlotType = *mut dyn io::Write;
    9|       |
   10|       |thread_local! {
   11|       |    static SLOT: RefCell<*mut SlotType> = const { RefCell::new(ptr::null_mut()) };
   12|       |}
   13|       |
   14|       |struct SlotGuard(*mut SlotType);
   15|       |
   16|       |impl SlotGuard {
   17|       |    #[must_use]
   18|      5|    fn new(cur: *mut SlotType) -> Self {
   19|      5|        let prev = SLOT.with(|slot| slot.replace(cur));
  ------------------
  | <scoped_writer::SlotGuard>::new::{closure#0}:
  |   19|      5|        let prev = SLOT.with(|slot| slot.replace(cur));
  ------------------
  | Unexecuted instantiation: <scoped_writer::SlotGuard>::new::{closure#0}
  ------------------
   20|      5|        SlotGuard(prev)
   21|      5|    }
  ------------------
  | <scoped_writer::SlotGuard>::new:
  |   18|      5|    fn new(cur: *mut SlotType) -> Self {
  |   19|      5|        let prev = SLOT.with(|slot| slot.replace(cur));
  |   20|      5|        SlotGuard(prev)
  |   21|      5|    }
  ------------------
  | Unexecuted instantiation: <scoped_writer::SlotGuard>::new
  ------------------
   22|       |}
   23|       |
   24|       |impl Drop for SlotGuard {
   25|      5|    fn drop(&mut self) {
   26|      5|        SLOT.with(|slot| *slot.borrow_mut() = self.0);
  ------------------
  | <scoped_writer::SlotGuard as core::ops::drop::Drop>::drop::{closure#0}:
  |   26|      5|        SLOT.with(|slot| *slot.borrow_mut() = self.0);
  ------------------
  | Unexecuted instantiation: <scoped_writer::SlotGuard as core::ops::drop::Drop>::drop::{closure#0}
  ------------------
   27|      5|    }
  ------------------
  | <scoped_writer::SlotGuard as core::ops::drop::Drop>::drop:
  |   25|      5|    fn drop(&mut self) {
  |   26|      5|        SLOT.with(|slot| *slot.borrow_mut() = self.0);
  |   27|      5|    }
  ------------------
  | Unexecuted instantiation: <scoped_writer::SlotGuard as core::ops::drop::Drop>::drop
  ------------------
   28|       |}
   29|       |
   30|       |/// Sets the global writer for the duration of the closure in current thread.
   31|      5|pub fn scoped<R>(mut w: &mut dyn io::Write, f: impl FnOnce() -> R) -> R {
   32|      5|    let _guard = SlotGuard::new(ptr::addr_of_mut!(w).cast());
   33|      5|    f()
   34|      5|}
  ------------------
  | scoped_writer::scoped::<core::option::Option<core::option::Option<()>>, basic::test_reentrancy::{closure#0}>:
  |   31|      1|pub fn scoped<R>(mut w: &mut dyn io::Write, f: impl FnOnce() -> R) -> R {
  |   32|      1|    let _guard = SlotGuard::new(ptr::addr_of_mut!(w).cast());
  |   33|      1|    f()
  |   34|      1|}
  ------------------
  | scoped_writer::scoped::<(), basic::test_panic::{closure#1}::{closure#0}::{closure#0}>:
  |   31|      1|pub fn scoped<R>(mut w: &mut dyn io::Write, f: impl FnOnce() -> R) -> R {
  |   32|      1|    let _guard = SlotGuard::new(ptr::addr_of_mut!(w).cast());
  |   33|      1|    f()
  |   34|      1|}
  ------------------
  | scoped_writer::scoped::<(), basic::test_panic::{closure#1}::{closure#0}>:
  |   31|      1|pub fn scoped<R>(mut w: &mut dyn io::Write, f: impl FnOnce() -> R) -> R {
  |   32|      1|    let _guard = SlotGuard::new(ptr::addr_of_mut!(w).cast());
  |   33|      1|    f()
  |   34|      1|}
  ------------------
  | scoped_writer::scoped::<(), basic::test_vec::{closure#0}>:
  |   31|      1|pub fn scoped<R>(mut w: &mut dyn io::Write, f: impl FnOnce() -> R) -> R {
  |   32|      1|    let _guard = SlotGuard::new(ptr::addr_of_mut!(w).cast());
  |   33|      1|    f()
  |   34|      1|}
  ------------------
  | scoped_writer::scoped::<(), basic::test_file::{closure#0}>:
  |   31|      1|pub fn scoped<R>(mut w: &mut dyn io::Write, f: impl FnOnce() -> R) -> R {
  |   32|      1|    let _guard = SlotGuard::new(ptr::addr_of_mut!(w).cast());
  |   33|      1|    f()
  |   34|      1|}
  ------------------
  | Unexecuted instantiation: scoped_writer::scoped::<_, _>
  ------------------
  | Unexecuted instantiation: scoped_writer::scoped::<_, _>
  ------------------
   35|       |
   36|       |/// Executes a closure with the global writer, skips if the writer is not set.
   37|       |///
   38|       |/// Reentrancy is not allowed.
   39|       |///
   40|       |/// # Panics
   41|       |/// Panics if this function is called recursively
   42|     12|pub fn with<R>(f: impl FnOnce(&mut dyn io::Write) -> R) -> Option<R> {
   43|     12|    SLOT.with(|slot| {
   44|     12|        let Ok(cur) = slot.try_borrow_mut() else {
                             ^11
   45|      1|            panic!("Reentrancy is not allowed")
   46|       |        };
   47|     11|        let p = cur.cast::<&mut dyn io::Write>();
   48|     11|        if p.is_null() {
   49|      4|            None
   50|       |        } else {
   51|      7|            Some(f(unsafe { &mut **p }))
   52|       |        }
   53|     12|    })
                  ^11
  ------------------
  | scoped_writer::with::<core::option::Option<()>, basic::test_reentrancy::{closure#0}::{closure#0}>::{closure#0}:
  |   43|      1|    SLOT.with(|slot| {
  |   44|      1|        let Ok(cur) = slot.try_borrow_mut() else {
  |   45|      0|            panic!("Reentrancy is not allowed")
  |   46|       |        };
  |   47|      1|        let p = cur.cast::<&mut dyn io::Write>();
  |   48|      1|        if p.is_null() {
  |   49|      0|            None
  |   50|       |        } else {
  |   51|      1|            Some(f(unsafe { &mut **p }))
  |   52|       |        }
  |   53|      1|    })
  ------------------
  | scoped_writer::with::<core::result::Result<(), std::io::error::Error>, basic::test_empty::{closure#0}>::{closure#0}:
  |   43|      1|    SLOT.with(|slot| {
  |   44|      1|        let Ok(cur) = slot.try_borrow_mut() else {
  |   45|      0|            panic!("Reentrancy is not allowed")
  |   46|       |        };
  |   47|      1|        let p = cur.cast::<&mut dyn io::Write>();
  |   48|      1|        if p.is_null() {
  |   49|      1|            None
  |   50|       |        } else {
  |   51|      0|            Some(f(unsafe { &mut **p }))
  |   52|       |        }
  |   53|      1|    })
  ------------------
  | scoped_writer::with::<core::result::Result<(), std::io::error::Error>, basic::test_panic::{closure#0}>::{closure#0}:
  |   43|      1|    SLOT.with(|slot| {
  |   44|      1|        let Ok(cur) = slot.try_borrow_mut() else {
  |   45|      0|            panic!("Reentrancy is not allowed")
  |   46|       |        };
  |   47|      1|        let p = cur.cast::<&mut dyn io::Write>();
  |   48|      1|        if p.is_null() {
  |   49|      1|            None
  |   50|       |        } else {
  |   51|      0|            Some(f(unsafe { &mut **p }))
  |   52|       |        }
  |   53|      1|    })
  ------------------
  | scoped_writer::with::<core::result::Result<(), std::io::error::Error>, basic::test_panic::{closure#2}>::{closure#0}:
  |   43|      1|    SLOT.with(|slot| {
  |   44|      1|        let Ok(cur) = slot.try_borrow_mut() else {
  |   45|      0|            panic!("Reentrancy is not allowed")
  |   46|       |        };
  |   47|      1|        let p = cur.cast::<&mut dyn io::Write>();
  |   48|      1|        if p.is_null() {
  |   49|      1|            None
  |   50|       |        } else {
  |   51|      0|            Some(f(unsafe { &mut **p }))
  |   52|       |        }
  |   53|      1|    })
  ------------------
  | scoped_writer::with::<(), scoped_writer::g<&str, [&str; 3]>::{closure#0}>::{closure#0}:
  |   43|      1|    SLOT.with(|slot| {
  |   44|      1|        let Ok(cur) = slot.try_borrow_mut() else {
  |   45|      0|            panic!("Reentrancy is not allowed")
  |   46|       |        };
  |   47|      1|        let p = cur.cast::<&mut dyn io::Write>();
  |   48|      1|        if p.is_null() {
  |   49|      0|            None
  |   50|       |        } else {
  |   51|      1|            Some(f(unsafe { &mut **p }))
  |   52|       |        }
  |   53|      1|    })
  ------------------
  | scoped_writer::with::<(), basic::test_reentrancy::{closure#0}::{closure#0}::{closure#0}>::{closure#0}:
  |   43|      1|    SLOT.with(|slot| {
  |   44|      1|        let Ok(cur) = slot.try_borrow_mut() else {
  |                             ^0
  |   45|      1|            panic!("Reentrancy is not allowed")
  |   46|       |        };
  |   47|      0|        let p = cur.cast::<&mut dyn io::Write>();
  |   48|      0|        if p.is_null() {
  |   49|      0|            None
  |   50|       |        } else {
  |   51|      0|            Some(f(unsafe { &mut **p }))
  |   52|       |        }
  |   53|      0|    })
  ------------------
  | scoped_writer::with::<(), basic::test_vec::{closure#0}::{closure#0}>::{closure#0}:
  |   43|      1|    SLOT.with(|slot| {
  |   44|      1|        let Ok(cur) = slot.try_borrow_mut() else {
  |   45|      0|            panic!("Reentrancy is not allowed")
  |   46|       |        };
  |   47|      1|        let p = cur.cast::<&mut dyn io::Write>();
  |   48|      1|        if p.is_null() {
  |   49|      0|            None
  |   50|       |        } else {
  |   51|      1|            Some(f(unsafe { &mut **p }))
  |   52|       |        }
  |   53|      1|    })
  ------------------
  | scoped_writer::with::<(), basic::test_vec::{closure#0}::{closure#2}>::{closure#0}:
  |   43|      1|    SLOT.with(|slot| {
  |   44|      1|        let Ok(cur) = slot.try_borrow_mut() else {
  |   45|      0|            panic!("Reentrancy is not allowed")
  |   46|       |        };
  |   47|      1|        let p = cur.cast::<&mut dyn io::Write>();
  |   48|      1|        if p.is_null() {
  |   49|      0|            None
  |   50|       |        } else {
  |   51|      1|            Some(f(unsafe { &mut **p }))
  |   52|       |        }
  |   53|      1|    })
  ------------------
  | scoped_writer::with::<(), basic::test_vec::{closure#0}::{closure#3}>::{closure#0}:
  |   43|      1|    SLOT.with(|slot| {
  |   44|      1|        let Ok(cur) = slot.try_borrow_mut() else {
  |   45|      0|            panic!("Reentrancy is not allowed")
  |   46|       |        };
  |   47|      1|        let p = cur.cast::<&mut dyn io::Write>();
  |   48|      1|        if p.is_null() {
  |   49|      0|            None
  |   50|       |        } else {
  |   51|      1|            Some(f(unsafe { &mut **p }))
  |   52|       |        }
  |   53|      1|    })
  ------------------
  | scoped_writer::with::<(), basic::test_vec::{closure#0}::{closure#4}>::{closure#0}:
  |   43|      1|    SLOT.with(|slot| {
  |   44|      1|        let Ok(cur) = slot.try_borrow_mut() else {
  |   45|      0|            panic!("Reentrancy is not allowed")
  |   46|       |        };
  |   47|      1|        let p = cur.cast::<&mut dyn io::Write>();
  |   48|      1|        if p.is_null() {
  |   49|      0|            None
  |   50|       |        } else {
  |   51|      1|            Some(f(unsafe { &mut **p }))
  |   52|       |        }
  |   53|      1|    })
  ------------------
  | scoped_writer::with::<(), basic::test_vec::{closure#0}::{closure#1}>::{closure#0}:
  |   43|      1|    SLOT.with(|slot| {
  |   44|      1|        let Ok(cur) = slot.try_borrow_mut() else {
  |   45|      0|            panic!("Reentrancy is not allowed")
  |   46|       |        };
  |   47|      1|        let p = cur.cast::<&mut dyn io::Write>();
  |   48|      1|        if p.is_null() {
  |   49|      0|            None
  |   50|       |        } else {
  |   51|      1|            Some(f(unsafe { &mut **p }))
  |   52|       |        }
  |   53|      1|    })
  ------------------
  | scoped_writer::with::<(), basic::test_match_arm::{closure#0}>::{closure#0}:
  |   43|      1|    SLOT.with(|slot| {
  |   44|      1|        let Ok(cur) = slot.try_borrow_mut() else {
  |   45|      0|            panic!("Reentrancy is not allowed")
  |   46|       |        };
  |   47|      1|        let p = cur.cast::<&mut dyn io::Write>();
  |   48|      1|        if p.is_null() {
  |   49|      1|            None
  |   50|       |        } else {
  |   51|      0|            Some(f(unsafe { &mut **p }))
  |   52|       |        }
  |   53|      1|    })
  ------------------
  | Unexecuted instantiation: scoped_writer::with::<_, _>::{closure#0}
  ------------------
  | Unexecuted instantiation: scoped_writer::with::<_, _>::{closure#0}
  ------------------
   54|     12|}
  ------------------
  | scoped_writer::with::<core::option::Option<()>, basic::test_reentrancy::{closure#0}::{closure#0}>:
  |   42|      1|pub fn with<R>(f: impl FnOnce(&mut dyn io::Write) -> R) -> Option<R> {
  |   43|      1|    SLOT.with(|slot| {
  |   44|       |        let Ok(cur) = slot.try_borrow_mut() else {
  |   45|       |            panic!("Reentrancy is not allowed")
  |   46|       |        };
  |   47|       |        let p = cur.cast::<&mut dyn io::Write>();
  |   48|       |        if p.is_null() {
  |   49|       |            None
  |   50|       |        } else {
  |   51|       |            Some(f(unsafe { &mut **p }))
  |   52|       |        }
  |   53|      1|    })
  |   54|      1|}
  ------------------
  | scoped_writer::with::<core::result::Result<(), std::io::error::Error>, basic::test_empty::{closure#0}>:
  |   42|      1|pub fn with<R>(f: impl FnOnce(&mut dyn io::Write) -> R) -> Option<R> {
  |   43|      1|    SLOT.with(|slot| {
  |   44|       |        let Ok(cur) = slot.try_borrow_mut() else {
  |   45|       |            panic!("Reentrancy is not allowed")
  |   46|       |        };
  |   47|       |        let p = cur.cast::<&mut dyn io::Write>();
  |   48|       |        if p.is_null() {
  |   49|       |            None
  |   50|       |        } else {
  |   51|       |            Some(f(unsafe { &mut **p }))
  |   52|       |        }
  |   53|      1|    })
  |   54|      1|}
  ------------------
  | scoped_writer::with::<core::result::Result<(), std::io::error::Error>, basic::test_panic::{closure#0}>:
  |   42|      1|pub fn with<R>(f: impl FnOnce(&mut dyn io::Write) -> R) -> Option<R> {
  |   43|      1|    SLOT.with(|slot| {
  |   44|       |        let Ok(cur) = slot.try_borrow_mut() else {
  |   45|       |            panic!("Reentrancy is not allowed")
  |   46|       |        };
  |   47|       |        let p = cur.cast::<&mut dyn io::Write>();
  |   48|       |        if p.is_null() {
  |   49|       |            None
  |   50|       |        } else {
  |   51|       |            Some(f(unsafe { &mut **p }))
  |   52|       |        }
  |   53|      1|    })
  |   54|      1|}
  ------------------
  | scoped_writer::with::<core::result::Result<(), std::io::error::Error>, basic::test_panic::{closure#2}>:
  |   42|      1|pub fn with<R>(f: impl FnOnce(&mut dyn io::Write) -> R) -> Option<R> {
  |   43|      1|    SLOT.with(|slot| {
  |   44|       |        let Ok(cur) = slot.try_borrow_mut() else {
  |   45|       |            panic!("Reentrancy is not allowed")
  |   46|       |        };
  |   47|       |        let p = cur.cast::<&mut dyn io::Write>();
  |   48|       |        if p.is_null() {
  |   49|       |            None
  |   50|       |        } else {
  |   51|       |            Some(f(unsafe { &mut **p }))
  |   52|       |        }
  |   53|      1|    })
  |   54|      1|}
  ------------------
  | scoped_writer::with::<(), scoped_writer::g<&str, [&str; 3]>::{closure#0}>:
  |   42|      1|pub fn with<R>(f: impl FnOnce(&mut dyn io::Write) -> R) -> Option<R> {
  |   43|      1|    SLOT.with(|slot| {
  |   44|       |        let Ok(cur) = slot.try_borrow_mut() else {
  |   45|       |            panic!("Reentrancy is not allowed")
  |   46|       |        };
  |   47|       |        let p = cur.cast::<&mut dyn io::Write>();
  |   48|       |        if p.is_null() {
  |   49|       |            None
  |   50|       |        } else {
  |   51|       |            Some(f(unsafe { &mut **p }))
  |   52|       |        }
  |   53|      1|    })
  |   54|      1|}
  ------------------
  | scoped_writer::with::<(), basic::test_reentrancy::{closure#0}::{closure#0}::{closure#0}>:
  |   42|      1|pub fn with<R>(f: impl FnOnce(&mut dyn io::Write) -> R) -> Option<R> {
  |   43|      1|    SLOT.with(|slot| {
  |   44|       |        let Ok(cur) = slot.try_borrow_mut() else {
  |   45|       |            panic!("Reentrancy is not allowed")
  |   46|       |        };
  |   47|       |        let p = cur.cast::<&mut dyn io::Write>();
  |   48|       |        if p.is_null() {
  |   49|       |            None
  |   50|       |        } else {
  |   51|       |            Some(f(unsafe { &mut **p }))
  |   52|       |        }
  |   53|      1|    })
  |   54|      1|}
  ------------------
  | scoped_writer::with::<(), basic::test_vec::{closure#0}::{closure#0}>:
  |   42|      1|pub fn with<R>(f: impl FnOnce(&mut dyn io::Write) -> R) -> Option<R> {
  |   43|      1|    SLOT.with(|slot| {
  |   44|       |        let Ok(cur) = slot.try_borrow_mut() else {
  |   45|       |            panic!("Reentrancy is not allowed")
  |   46|       |        };
  |   47|       |        let p = cur.cast::<&mut dyn io::Write>();
  |   48|       |        if p.is_null() {
  |   49|       |            None
  |   50|       |        } else {
  |   51|       |            Some(f(unsafe { &mut **p }))
  |   52|       |        }
  |   53|      1|    })
  |   54|      1|}
  ------------------
  | scoped_writer::with::<(), basic::test_vec::{closure#0}::{closure#2}>:
  |   42|      1|pub fn with<R>(f: impl FnOnce(&mut dyn io::Write) -> R) -> Option<R> {
  |   43|      1|    SLOT.with(|slot| {
  |   44|       |        let Ok(cur) = slot.try_borrow_mut() else {
  |   45|       |            panic!("Reentrancy is not allowed")
  |   46|       |        };
  |   47|       |        let p = cur.cast::<&mut dyn io::Write>();
  |   48|       |        if p.is_null() {
  |   49|       |            None
  |   50|       |        } else {
  |   51|       |            Some(f(unsafe { &mut **p }))
  |   52|       |        }
  |   53|      1|    })
  |   54|      1|}
  ------------------
  | scoped_writer::with::<(), basic::test_vec::{closure#0}::{closure#3}>:
  |   42|      1|pub fn with<R>(f: impl FnOnce(&mut dyn io::Write) -> R) -> Option<R> {
  |   43|      1|    SLOT.with(|slot| {
  |   44|       |        let Ok(cur) = slot.try_borrow_mut() else {
  |   45|       |            panic!("Reentrancy is not allowed")
  |   46|       |        };
  |   47|       |        let p = cur.cast::<&mut dyn io::Write>();
  |   48|       |        if p.is_null() {
  |   49|       |            None
  |   50|       |        } else {
  |   51|       |            Some(f(unsafe { &mut **p }))
  |   52|       |        }
  |   53|      1|    })
  |   54|      1|}
  ------------------
  | scoped_writer::with::<(), basic::test_vec::{closure#0}::{closure#4}>:
  |   42|      1|pub fn with<R>(f: impl FnOnce(&mut dyn io::Write) -> R) -> Option<R> {
  |   43|      1|    SLOT.with(|slot| {
  |   44|       |        let Ok(cur) = slot.try_borrow_mut() else {
  |   45|       |            panic!("Reentrancy is not allowed")
  |   46|       |        };
  |   47|       |        let p = cur.cast::<&mut dyn io::Write>();
  |   48|       |        if p.is_null() {
  |   49|       |            None
  |   50|       |        } else {
  |   51|       |            Some(f(unsafe { &mut **p }))
  |   52|       |        }
  |   53|      1|    })
  |   54|      1|}
  ------------------
  | scoped_writer::with::<(), basic::test_vec::{closure#0}::{closure#1}>:
  |   42|      1|pub fn with<R>(f: impl FnOnce(&mut dyn io::Write) -> R) -> Option<R> {
  |   43|      1|    SLOT.with(|slot| {
  |   44|       |        let Ok(cur) = slot.try_borrow_mut() else {
  |   45|       |            panic!("Reentrancy is not allowed")
  |   46|       |        };
  |   47|       |        let p = cur.cast::<&mut dyn io::Write>();
  |   48|       |        if p.is_null() {
  |   49|       |            None
  |   50|       |        } else {
  |   51|       |            Some(f(unsafe { &mut **p }))
  |   52|       |        }
  |   53|      1|    })
  |   54|      1|}
  ------------------
  | scoped_writer::with::<(), basic::test_match_arm::{closure#0}>:
  |   42|      1|pub fn with<R>(f: impl FnOnce(&mut dyn io::Write) -> R) -> Option<R> {
  |   43|      1|    SLOT.with(|slot| {
  |   44|       |        let Ok(cur) = slot.try_borrow_mut() else {
  |   45|       |            panic!("Reentrancy is not allowed")
  |   46|       |        };
  |   47|       |        let p = cur.cast::<&mut dyn io::Write>();
  |   48|       |        if p.is_null() {
  |   49|       |            None
  |   50|       |        } else {
  |   51|       |            Some(f(unsafe { &mut **p }))
  |   52|       |        }
  |   53|      1|    })
  |   54|      1|}
  ------------------
  | Unexecuted instantiation: scoped_writer::with::<_, _>
  ------------------
  | Unexecuted instantiation: scoped_writer::with::<_, _>
  ------------------
   55|       |
   56|       |/// [`writeln!`] to the global writer.
   57|       |#[macro_export]
   58|       |macro_rules! g {
   59|       |    () => {{
   60|      1|        $crate::with(|w|writeln!(w).unwrap());
  ------------------
  | basic::test_vec::{closure#0}::{closure#1}:
  |   60|      1|        $crate::with(|w|writeln!(w).unwrap());
  ------------------
  | Unexecuted instantiation: basic::test_match_arm::{closure#0}
  ------------------
   61|       |    }};
   62|       |    ($fmt:literal $($arg:tt)*) => {{
   63|      4|        $crate::with(|w|writeln!(w, $fmt $($arg)*).unwrap());
  ------------------
  | basic::test_vec::{closure#0}::{closure#0}:
  |   63|      1|        $crate::with(|w|writeln!(w, $fmt $($arg)*).unwrap());
  ------------------
  | basic::test_vec::{closure#0}::{closure#2}:
  |   63|      1|        $crate::with(|w|writeln!(w, $fmt $($arg)*).unwrap());
  ------------------
  | basic::test_vec::{closure#0}::{closure#3}:
  |   63|      1|        $crate::with(|w|writeln!(w, $fmt $($arg)*).unwrap());
  ------------------
  | basic::test_vec::{closure#0}::{closure#4}:
  |   63|      1|        $crate::with(|w|writeln!(w, $fmt $($arg)*).unwrap());
  ------------------
   64|       |    }};
   65|       |}
   66|       |
   67|       |/// Writes lines to the global writer.
   68|      1|pub fn g<L>(lines: impl AsRef<[L]>)
   69|      1|where
   70|      1|    L: AsRef<str>,
   71|      1|{
   72|      1|    with(|w| {
   73|      3|        for line in lines.as_ref() {
                                  ^1
   74|      3|            writeln!(w, "{}", line.as_ref()).unwrap();
   75|      3|        }
   76|      1|    });
  ------------------
  | scoped_writer::g::<&str, [&str; 3]>::{closure#0}:
  |   72|      1|    with(|w| {
  |   73|      3|        for line in lines.as_ref() {
  |                                  ^1
  |   74|      3|            writeln!(w, "{}", line.as_ref()).unwrap();
  |   75|      3|        }
  |   76|      1|    });
  ------------------
  | Unexecuted instantiation: scoped_writer::g::<_, _>::{closure#0}
  ------------------
  | Unexecuted instantiation: scoped_writer::g::<_, _>::{closure#0}
  ------------------
   77|      1|}
  ------------------
  | scoped_writer::g::<&str, [&str; 3]>:
  |   68|      1|pub fn g<L>(lines: impl AsRef<[L]>)
  |   69|      1|where
  |   70|      1|    L: AsRef<str>,
  |   71|      1|{
  |   72|      1|    with(|w| {
  |   73|       |        for line in lines.as_ref() {
  |   74|       |            writeln!(w, "{}", line.as_ref()).unwrap();
  |   75|       |        }
  |   76|      1|    });
  |   77|      1|}
  ------------------
  | Unexecuted instantiation: scoped_writer::g::<_, _>
  ------------------
  | Unexecuted instantiation: scoped_writer::g::<_, _>
  ------------------

I haven't fully understood what the report means. And how to fix it?

[frederico-monteiro]

Ah, I think what's happening is that the closures in g! are being instantiated at multiple sites in the test file.

Some of those instantiations are unused, but others are used, and the used ones appear to have made the unused ones invisible, even though they are still counted in the totals.

Does running cargo llvm-cov with --show-instantiations make the uncovered regions visible in the report?

It seems this behavior aligns precisely with what you described. Specifically, closures instantiated at multiple sites in the test file cause some unused instantiations to remain invisible, despite being included in the overall coverage totals.

By running cargo llvm-cov with the --show-instantiations flag does indeed make the uncovered regions visible in the report and I am experiencing the exact same problem.

Is there a timeline or road-map for addressing this issue?