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lldb hashmap pretty printer broken #81814
Description
The LLDB provider for hash maps has been broken since #79234.
Repro:
use std::collections::*;
fn main() {
let mut map = HashMap::new();
map.insert(1, 2);
eprintln!("{:?}", map);
}Run this, notice that it doesn't print any values for the hash map:
rustc -g foo.rs
rust-lldb foo
(lldb) b 5
(lldb) r
(lldb) p map
(std::collections::hash::map::HashMap<int, int, std::collections::hash::map::RandomState>) $0 = size=1 {}
Using an older version works (1.49 or earler):
(lldb) p map
(std::collections::hash::map::HashMap<int, int, std::collections::hash::map::RandomState>) $0 = size=1 {
[0] = {
0 = 1
1 = 2
}
}
I don't understand the motivation for #79234, as you can see the older versions are able to display the type. @ortem can you clarify what is going on?
I did some debugging, and the pair_type_size and data_ptr values are invalid.
Another way to check this is to run the src/test/debuginfo/pretty-std-collections.rs test. Due to #81813 it hasn't been running on CI.
It has a check for the following output:
$2 = size=4 { [0] = { 0 = 1 1 = 10 } [1] = { 0 = 2 1 = 20 } [2] = { 0 = 3 1 = 30 } [3] = { 0 = 4 1 = 40 } }
$3 = size=4 { [0] = 1 [1] = 2 [2] = 3 [3] = 4 }
But the actual output is:
$2 = size=4 {}
$3 = size=4 {}
Activity
artemmukhin commentedon Feb 6, 2021
@ehuss I checked the issue with two different LLDB:
rust-lldbshipped with1.51.0-nightlyby adding the following code to the
StdHashMapSyntheticProvider#updatemethod:rust-lldbLLVM upstream with Rust patches
So it seems like the problem only occurs with
rust-lldb.Probably this is due to the lack of Rust patches in
rust-lldb. AFAIU the Rust patches still have not been added torust-lldb(I remember this related issue rust-lang/lldb#20).To fix this problem, the following code should be used insted:
I've opened a PR with these changes: #81834.
However, I believe that
rust-lldbshould use Rust patches not only to avoid this specific problem but to provide a much better debugging experience, with proper type rendering (e.g.i32instead ofint), some expression evaluation support, and so forth. It is really unfortunate that Rust debugging support is not maintained enough except for some independent forks, for example, https://github.com/vadimcn/llvm-project/commits/rust-lldb and CLion's LLDB.ehuss commentedon Feb 6, 2021
I may be misunderstanding you, but
rust-lldbis just a shell script that runs the system lldb. Building lldb with patches was removed a long time ago (#62592), and I suspect is not coming back in the foreseeable future.artemmukhin commentedon Feb 6, 2021
@ehuss Oh, that's even worse since macOS LLDB has very poor Rust support. I believe that debugging support is crucial for any compiled programming language, surely including Rust. So it would be really great to consider shipping rust-enabled LLDB and, more importantly, to maintain and improve Rust support in both GDB and LLDB.
Rollup merge of rust-lang#81834 - ortem:fix-LLDB-hashmap-pretty-print…