Make backtrace function names and spans match up #1283
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Apr 1, 2020
Miri: make backtrace function names and spans match up
Currently, Miri backtraces are a bit confusing:
```
error: Undefined Behavior: entering unreachable code
--> tests/compile-fail/never_transmute_void.rs:10:11
|
10 | match v {} //~ ERROR entering unreachable code
| ^ entering unreachable code
|
= help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
= help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
note: inside call to `f` at tests/compile-fail/never_transmute_void.rs:17:5
--> tests/compile-fail/never_transmute_void.rs:17:5
|
17 | f(v); //~ inside call to `f`
| ^^^^
= note: inside call to `main` at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/rt.rs:67:34
= note: inside call to closure at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/rt.rs:52:73
= note: inside call to closure at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/sys_common/backtrace.rs:130:5
```
When reading this like a normal backtrace, one would expect that e.g. the backrace involves the "main" function at "libstd/rt.rs:67:34". But that is not actually where we are in the main function, that is *where the main function is called*.
This is not how backtraces are usually rendered (including e.g. with `RUST_BACKTRACE=1`). Usually we print next to each function name where inside that function the frame is currently executing, not where the *parent* frame is executing. With this PR and the Miri side at rust-lang/miri#1283, the backtrace now looks as follows:
```
error: Undefined Behavior: entering unreachable code
--> tests/compile-fail/never_transmute_void.rs:10:11
|
10 | match v {} //~ ERROR entering unreachable code
| ^ entering unreachable code
|
= help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
= help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
= note: inside `f` at tests/compile-fail/never_transmute_void.rs:10:11
note: inside `main` at tests/compile-fail/never_transmute_void.rs:17:5
--> tests/compile-fail/never_transmute_void.rs:17:5
|
17 | f(v); //~ inside `main`
| ^^^^
= note: inside closure at /home/r/src/rust/rustc/src/libstd/rt.rs:67:34
= note: inside closure at /home/r/src/rust/rustc/src/libstd/rt.rs:52:73
= note: inside `std::sys_common::backtrace::__rust_begin_short_backtrace::<[closure@DefId(1:6034 ~ std[87db]::rt[0]::lang_start_internal[0]::{{closure}}[0]::{{closure}}[0]) 0:&dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe], i32>` at /home/r/src/rust/rustc/src/libstd/sys_common/backtrace.rs:130:5
```
Now function name and printed line numbers match up in the notes.
This code is partially shared with const-eval, so the change also affects const-eval: instead of printing what is being called at some span, we print which function/constant this span is inside.
With this, we can also remove the `span` field from Miri's stack frames (which used to track the *caller span* of that frame, quite confusing), and then get of a whole lot of `span` arguments that ultimately just served to fill that field (and as a fallback for `caller_location`, which however was never actually used).
r? @oli-obk
|
@bors r+ |
|
📌 Commit 5ce2466 has been approved by |
|
☀️ Test successful - checks-travis, status-appveyor |
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This is the Miri side of rust-lang/rust#70590.
Fixes #521