Debug-printing geometries segfaults

[lnicola]

Something like:

fn main() -> Result<()> {
    let args = std::env::args().collect::<Vec<_>>();
    let point_ds = Dataset::open(&args[1])?;
    let mut layer = point_ds.layer(0)?;
    for feature in layer.features() {
        dbg!(feature);
    }
    Ok(())
}

crashes with:

[src/main.rs:17] feature = Feature {
    _defn: Defn {
        c_defn: 0x0000562e86c81c80,
    },
    c_feature: 0x0000562e86c85d60,
    geometry: [
thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', ~/.cargo/registry/src/github.aaakk.us.kg-1ecc6299db9ec823/gdal-0.14.0/src/vector/geometry.rs:177:38
stack backtrace:
   0: rust_begin_unwind
             at /rustc/efd27454ae94386e11997b1158f60d3a79deeb7d/library/std/src/panicking.rs:575:5
   1: core::panicking::panic_fmt
             at /rustc/efd27454ae94386e11997b1158f60d3a79deeb7d/library/core/src/panicking.rs:64:14
   2: core::panicking::panic
             at /rustc/efd27454ae94386e11997b1158f60d3a79deeb7d/library/core/src/panicking.rs:114:5
   3: gdal::vector::geometry::Geometry::wkt
   4: <&T as core::fmt::Debug>::fmt

[metasim]

@lnicola Was going to replicate on MacOS. Can you share the input file?

[lnicola]

It happens with every input, like the sample from https://github.com/ngageoint/GeoPackage/blob/master/docs/examples/java/example.gpkg.

Tested with the crates.io version, though.

[metasim]

FWIW, here's what I get from master:

     Running `.../georust-gdal/target/debug/examples/segfault ./example.gpkg`
Warning 1: Database relies on the 'nga_contents_id' (http://ngageoint.github.io/GeoPackage/docs/extensions/contents-id.html) extension that should be implemented in order to read it safely, but is not currently. Some data may be missing while reading that database.
Warning 1: Database relies on the 'nga_feature_tile_link' (http://ngageoint.github.io/GeoPackage/docs/extensions/feature-tile-link.html) extension that should be implemented in order to read it safely, but is not currently. Some data may be missing while reading that database.
Warning 1: Layer point1 relies on the 'nga_geometry_index' (http://ngageoint.github.io/GeoPackage/docs/extensions/geometry-index.html) extension that should be implemented in order to read it safely, but is not currently. Some data may be missing while reading that layer.
[examples/segfault.rs:9] feature = Feature {
    _defn: Defn {
        c_defn: 0x000060000304afd0,
    },
    c_feature: 0x00006000030763f0,
    geometry: [
thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', src/vector/geometry.rs:177:38

[metasim]

Not really the problem, but calling unwrap seems like a bad idea?

gdal/src/vector/geometry.rs

Line 177 in c7f88b5

self.c_geometry_ref.borrow().unwrap()

[metasim]

@lnicola I wonder if this (foreign_types) or something like it might be worth considering. I think we need some principled semantics around these GDAL pointers, Rust has all the type machinery we need, we just need to find good examples of how to do this properly or rely on a library that does it for us.

[lnicola]

Still haven't looked into it, but I think we handle layers in a better way, that could serve as inspiration.

[metasim]

I have foreign_types prototype here: master...metasim:gdal:prototype/foreign_types

Personally, once I converted a couple types, I really liked it (except the paucity of documentation), especially since it explicitly distinguishes owned vs. borrowed types. It's a very principled API. However, there would be several breaking changes.