specific errors and try_into for inner geo-types

CHANGES.md

@@ -2,6 +2,11 @@
 
 ## Unreleased
 
+* WKT errors impl `std::error::Error`
+  * <https://github.com/georust/wkt/pull/56/>
+* Add TryFrom for converting directly to geo-types::Geometry enum members, such
+  as `geo_types::LineString::try_from(wkt)`
+  * <https://github.com/georust/wkt/pull/56/>
 * Add `geo-types::Geometry::from(wkt)`
 * BREAKING: update geo-types, apply new `geo_types::CoordFloat`
   * <https://github.com/georust/wkt/pull/53>

Cargo.toml

@@ -12,6 +12,7 @@ keywords = ["geo", "geospatial", "wkt"]
 [dependencies]
 geo-types = {version = "0.7", optional = true}
 num-traits = "0.2"
+thiserror = "1.0.23"
 
 [dev-dependencies]
 criterion = { version = "0.2" }
@@ -22,3 +23,12 @@ default = ["geo-types"]
 [[bench]]
 name = "parse"
 harness = false
+
+[patch.crates-io]
+# This feature depends on an unmerged geo-types feature.
+# Once (and if) that geo-types feature is released, we can merge this and bump
+# the min version of geo-types required.
+# That's a breaking change for wkt, but we already have an unreleased breaking
+# change for WKT in the pipeline, so I'd recommend combinging them into one
+# breaking WKT release.
+geo-types = { git = "https://github.com/georust/geo", branch = "mkirk/pub-error" }

src/conversion.rs

@@ -17,23 +17,23 @@ use Geometry;
 use Wkt;
 
 use std::convert::{TryFrom, TryInto};
-use std::fmt;
 
 use geo_types::CoordFloat;
+use thiserror::Error;
 
-#[derive(Debug)]
+#[derive(Error, Debug)]
 pub enum Error {
+    #[error("The WKT Point was empty, but geo_type::Points cannot be empty")]
     PointConversionError,
-}
-
-impl fmt::Display for Error {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match *self {
-            Error::PointConversionError => {
-                f.write_str("impossible to convert empty point to geo_type point")
-            }
-        }
-    }
+    #[error("Mismatched geometry (expected {expected:?}, found {found:?})")]
+    MismatchedGeometry {
+        expected: &'static str,
+        found: &'static str,
+    },
+    #[error("Wrong number of Geometries: {0}")]
+    WrongNumberOfGeometries(usize),
+    #[error("External error: {0}")]
+    External(Box<dyn std::error::Error>),
 }
 
 impl<T> TryFrom<Wkt<T>> for geo_types::Geometry<T>
@@ -51,6 +51,50 @@ where
     }
 }
 
+#[macro_use]
+macro_rules! try_from_wkt_impl {
+    ($($type: ident),+) => {
+        $(
+            /// Convert a Wkt enum into a specific geo-type
+            impl<T: CoordFloat> TryFrom<Wkt<T>> for geo_types::$type<T> {
+                type Error = Error;
+
+                fn try_from(mut wkt: Wkt<T>) -> Result<Self, Self::Error> {
+                    match wkt.items.len() {
+                        1 => {
+                            let item = wkt.items.pop().unwrap();
+                            let geometry = geo_types::Geometry::try_from(item)?;
+                            Self::try_from(geometry).map_err(|e| {
+                                match e {
+                                    geo_types::Error::MismatchedGeometry { expected, found } => {
+                                        Error::MismatchedGeometry { expected, found }
+                                    }
+                                    // currently only one error type in geo-types error enum, but that seems likely to change
+                                    #[allow(unreachable_patterns)]
+                                    other => Error::External(Box::new(other)),
+                                }
+                            })
+                        }
+                        other => Err(Error::WrongNumberOfGeometries(other)),
+                    }
+                }
+            }
+        )+
+    }
+}
+
+try_from_wkt_impl!(
+    Point,
+    Line,
+    LineString,
+    Polygon,
+    MultiPoint,
+    MultiLineString,
+    MultiPolygon,
+    Rect,
+    Triangle
+);
+
 impl<T> From<Coord<T>> for geo_types::Coordinate<T>
 where
     T: CoordFloat,

src/lib.rs

@@ -35,6 +35,8 @@ pub mod types;
 #[cfg(feature = "geo-types")]
 extern crate geo_types;
 
+extern crate thiserror;
+
 #[cfg(feature = "geo-types")]
 pub use towkt::ToWkt;