Handle singleton structs in Rust

12 files changed, 86 insertions, 40 deletions

diff --git a/examples/02-struct-singleton/output/rust/src/point.rs b/examples/02-struct-singleton/output/rust/src/point.rs
index e2d608c..866f0c5 100644
--- a/examples/02-struct-singleton/output/rust/src/point.rs
+++ b/examples/02-struct-singleton/output/rust/src/point.rs
@@ -1,5 +1,4 @@
 // Generated by hobgoblin.
 
 #[derive(Debug, Hash, PartialEq)]
-pub struct Origin {
-}
+pub struct Origin;
diff --git a/examples/12-transient-0/output/java/src/test/java/org/zwobble/example/Transient0Tests.java b/examples/12-transient-0/output/java/src/test/java/org/zwobble/example/Transient0Tests.java
index a924d1e..d8d4f3f 100644
--- a/examples/12-transient-0/output/java/src/test/java/org/zwobble/example/Transient0Tests.java
+++ b/examples/12-transient-0/output/java/src/test/java/org/zwobble/example/Transient0Tests.java
@@ -15,6 +15,7 @@ import java.util.Optional;
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
 import org.zwobble.example.types.data.EnumWithVariants;
+import org.zwobble.example.types.data.StructSingleton;
 import org.zwobble.example.types.data.StructWithBool;
 import org.zwobble.example.types.data.StructWithDifferentSharedTypes;
 import org.zwobble.example.types.data.StructWithEnum;
@@ -34,6 +35,18 @@ import org.zwobble.example.types.transient0.HobgoblinTransient0TaggedSharedValue
 
 public class Transient0Tests {
     @Test
+    public void structSingleton() throws IOException {
+        var value = StructSingleton.INSTANCE;
+
+        assertRoundTripEncoding(
+            "StructSingleton",
+            value,
+            HobgoblinTransient0Data::encodeStructSingleton,
+            HobgoblinTransient0Data::decodeStructSingleton
+        );
+    }
+
+    @Test
     public void structWithBool() throws IOException {
         var value = new StructWithBool(true, false);
 
diff --git a/examples/12-transient-0/output/rust/src/gen/data.rs b/examples/12-transient-0/output/rust/src/gen/data.rs
index 4ec0524..aef9f69 100644
--- a/examples/12-transient-0/output/rust/src/gen/data.rs
+++ b/examples/12-transient-0/output/rust/src/gen/data.rs
@@ -1,6 +1,9 @@
 // Generated by hobgoblin.
 
 #[derive(Debug, Hash, PartialEq)]
+pub struct StructSingleton;
+
+#[derive(Debug, Hash, PartialEq)]
 pub struct StructWithBool {
     pub a: ::core::primitive::bool,
     pub b: ::core::primitive::bool,
diff --git a/examples/12-transient-0/output/rust/src/gen/data/transient_0.rs b/examples/12-transient-0/output/rust/src/gen/data/transient_0.rs
index ea4a459..ca9beaf 100644
--- a/examples/12-transient-0/output/rust/src/gen/data/transient_0.rs
+++ b/examples/12-transient-0/output/rust/src/gen/data/transient_0.rs
@@ -1,5 +1,13 @@
 // Generated by hobgoblin.
 
+pub fn encode_struct_singleton(value: &crate::data::StructSingleton, writer: &mut impl std::io::Write, shared_values: &mut ::std::collections::HashMap::<::core::primitive::usize, ::core::primitive::i64>) -> ::std::io::Result::<()> {
+    ::std::io::Result::Ok(())
+}
+
+pub fn decode_struct_singleton(reader: &mut impl std::io::Read, shared_values: &mut ::std::vec::Vec::<::std::sync::Arc::<dyn ::std::any::Any + ::std::marker::Sync + ::std::marker::Send>>) -> ::std::io::Result::<crate::data::StructSingleton> {
+    ::std::io::Result::Ok(crate::data::StructSingleton)
+}
+
 pub fn encode_struct_with_bool(value: &crate::data::StructWithBool, writer: &mut impl std::io::Write, shared_values: &mut ::std::collections::HashMap::<::core::primitive::usize, ::core::primitive::i64>) -> ::std::io::Result::<()> {
     crate::transient_0::encode_bool(&value.a, writer, shared_values)?;
     crate::transient_0::encode_bool(&value.b, writer, shared_values)?;
diff --git a/examples/12-transient-0/output/rust/src/lib.rs b/examples/12-transient-0/output/rust/src/lib.rs
index 3a02936..365a352 100644
--- a/examples/12-transient-0/output/rust/src/lib.rs
+++ b/examples/12-transient-0/output/rust/src/lib.rs
@@ -8,7 +8,19 @@ mod test {
     use std::path::PathBuf;
     use std::sync::Arc;
     use std::collections::HashMap;
-    use super::data::{EnumWithVariants, StructWithBool, StructWithDifferentSharedTypes, StructWithEnum, StructWithInt32, StructWithInt64, StructWithList, StructWithListOfShared, StructWithOption, StructWithSharedSumAndVariant, StructWithString, StructWithStruct, StructWithSum, SumWithVariants, VariantOne, VariantTwo };
+    use super::data::{EnumWithVariants, StructSingleton, StructWithBool, StructWithDifferentSharedTypes, StructWithEnum, StructWithInt32, StructWithInt64, StructWithList, StructWithListOfShared, StructWithOption, StructWithSharedSumAndVariant, StructWithString, StructWithStruct, StructWithSum, SumWithVariants, VariantOne, VariantTwo };
+
+    #[test]
+    fn struct_singleton() {
+        let value = StructSingleton;
+
+        assert_round_trip_encoding(
+            "StructSingleton",
+            value,
+            super::data::transient_0::encode_struct_singleton,
+            super::data::transient_0::decode_struct_singleton,
+        );
+    }
 
     #[test]
     fn struct_with_bool() {
diff --git a/examples/12-transient-0/src/data.hob b/examples/12-transient-0/src/data.hob
index 9c715e9..0a55e39 100644
--- a/examples/12-transient-0/src/data.hob
+++ b/examples/12-transient-0/src/data.hob
@@ -1,3 +1,7 @@
+struct StructSingleton {
+    singleton;
+}
+
 struct StructWithBool {
     field a: Bool;
     field b: Bool;
diff --git a/hobgoblin/src/output/lang/rust/ast.hob b/hobgoblin/src/output/lang/rust/ast.hob
index f1a4513..1fbfa99 100644
--- a/hobgoblin/src/output/lang/rust/ast.hob
+++ b/hobgoblin/src/output/lang/rust/ast.hob
@@ -37,7 +37,7 @@ struct RustFunctionParam {
 struct RustStructStruct {
     field attributes: List[RustOuterAttribute];
     field name: RustIdentifier;
-    field fields: List[RustStructField];
+    field fields: Option[List[RustStructField]];
     field docComment: DocComment;
 }
 
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/rusttypes/RustTypesGenerator.java b/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/rusttypes/RustTypesGenerator.java
index 8ed9d9e..39a0b8b 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/rusttypes/RustTypesGenerator.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/output/generators/rusttypes/RustTypesGenerator.java
@@ -127,12 +127,14 @@ public class RustTypesGenerator implements Generator {
 
         var rustStructName = this.rustGenerator.generateTypeName(structDefinition.name());
 
-        var rustFields = structDefinition.fields().orElse(List.of()).stream()
-            .map(field -> new RustStructField(
-                this.rustGenerator.generateFieldName(field.name()),
-                generateRustTypeExpression(field.type(), context)
-            ))
-            .toList();
+        var rustFields = structDefinition.fields().map(
+            fields -> fields.stream()
+                .map(field -> new RustStructField(
+                    this.rustGenerator.generateFieldName(field.name()),
+                    generateRustTypeExpression(field.type(), context)
+                ))
+                .toList()
+        );
 
         var rustStruct = new RustStructStruct(
             rustAttributes,
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/output/lang/rust/RustWriter.java b/src/main/java/org/zwobble/hobgoblin/compiler/output/lang/rust/RustWriter.java
index d0552ad..668cd75 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/output/lang/rust/RustWriter.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/output/lang/rust/RustWriter.java
@@ -136,12 +136,14 @@ public class RustWriter implements AutoCloseable {
         this.writerOuterAttributes(structStruct.attributes());
         this.writer.write("pub struct ");
         this.writeIdentifier(structStruct.name());
-        this.writer.write(" {");
 
-        if (!structStruct.fields().isEmpty()) {
+        if (structStruct.fields().isEmpty()) {
+            this.writer.write(";");
+        } else {
+            this.writer.write(" {");
             this.writer.indent();
 
-            for (var field : structStruct.fields()) {
+            for (var field : structStruct.fields().get()) {
                 this.writer.newLine();
                 this.writer.write("pub ");
                 this.writeIdentifier(field.name());
@@ -151,10 +153,9 @@ public class RustWriter implements AutoCloseable {
             }
 
             this.writer.dedent();
+            this.writer.newLine();
+            this.writer.write("}");
         }
-
-        this.writer.newLine();
-        this.writer.write("}");
     }
 
     // === Enumerations ===
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/output/lang/rust/ast/RustStructStruct.java b/src/main/java/org/zwobble/hobgoblin/compiler/output/lang/rust/ast/RustStructStruct.java
index 4bc3a1e..2838a68 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/output/lang/rust/ast/RustStructStruct.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/output/lang/rust/ast/RustStructStruct.java
@@ -8,17 +8,17 @@ package org.zwobble.hobgoblin.compiler.output.lang.rust.ast;
 public record RustStructStruct(
     java.util.List<org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustOuterAttribute> attributes,
     org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustIdentifier name,
-    java.util.List<org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructField> fields,
+    java.util.Optional<java.util.List<org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructField>> fields,
     org.zwobble.hobgoblin.compiler.ast.DocComment docComment
 ) implements org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustItem {
     public static org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructStruct.Builder arbitrary() {
-        return new org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructStruct.Builder(java.util.List.of(), org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustIdentifier.arbitrary().build(), java.util.List.of(), org.zwobble.hobgoblin.compiler.ast.HobgoblinNativeAst.arbitraryDocComment());
+        return new org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructStruct.Builder(java.util.List.of(), org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustIdentifier.arbitrary().build(), java.util.Optional.empty(), org.zwobble.hobgoblin.compiler.ast.HobgoblinNativeAst.arbitraryDocComment());
     }
 
     public record Builder(
         java.util.List<org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustOuterAttribute> attributes,
         org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustIdentifier name,
-        java.util.List<org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructField> fields,
+        java.util.Optional<java.util.List<org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructField>> fields,
         org.zwobble.hobgoblin.compiler.ast.DocComment docComment
     ) implements org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustItem.Builder {
         public org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructStruct build() {
@@ -49,20 +49,12 @@ public record RustStructStruct(
             return new org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructStruct.Builder(attributes, name.build(), fields, docComment);
         }
 
-        public org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructStruct.Builder withFields(java.util.List<org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructField> fields) {
-            return new org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructStruct.Builder(attributes, name, fields, docComment);
-        }
-
-        public org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructStruct.Builder addField(org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructField field) {
-            var fields = new java.util.ArrayList<org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructField>(this.fields);
-            fields.add(field);
+        public org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructStruct.Builder withFields(java.util.Optional<java.util.List<org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructField>> fields) {
             return new org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructStruct.Builder(attributes, name, fields, docComment);
         }
 
-        public org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructStruct.Builder addField(org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructField.Builder field) {
-            var fields = new java.util.ArrayList<org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructField>(this.fields);
-            fields.add(field.build());
-            return new org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructStruct.Builder(attributes, name, fields, docComment);
+        public org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructStruct.Builder withFields(java.util.List<org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructField> fields) {
+            return new org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructStruct.Builder(attributes, name, java.util.Optional.of(fields), docComment);
         }
 
         public org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructStruct.Builder withDocComment(org.zwobble.hobgoblin.compiler.ast.DocComment docComment) {
diff --git a/src/test/java/org/zwobble/hobgoblin/compiler/output/lang/rust/RustWriterTests.java b/src/test/java/org/zwobble/hobgoblin/compiler/output/lang/rust/RustWriterTests.java
index 4a81031..56d6d87 100644
--- a/src/test/java/org/zwobble/hobgoblin/compiler/output/lang/rust/RustWriterTests.java
+++ b/src/test/java/org/zwobble/hobgoblin/compiler/output/lang/rust/RustWriterTests.java
@@ -28,11 +28,9 @@ public class RustWriterTests {
         assertThat(string, equalTo("""
             // Generated by hobgoblin.
 
-            pub struct Rectangle {
-            }
+            pub struct Rectangle;
             
-            pub struct Square {
-            }
+            pub struct Square;
             """));
     }
 
@@ -112,8 +110,24 @@ public class RustWriterTests {
     // === Structs ===
 
     @Test
+    public void unitLikeStruct() throws IOException {
+        var rust = RustStructStruct.arbitrary()
+            .withName(new RustIdentifier("Rectangle"))
+            .withFields(Optional.empty())
+            .build();
+
+        var string = write(writer -> writer.writeItem(rust));
+
+        assertThat(string, equalTo("""
+            pub struct Rectangle;"""));
+    }
+
+    @Test
     public void emptyStruct() throws IOException {
-        var rust = RustStructStruct.arbitrary().withName(new RustIdentifier("Rectangle")).build();
+        var rust = RustStructStruct.arbitrary()
+            .withName(new RustIdentifier("Rectangle"))
+            .withFields(List.of())
+            .build();
 
         var string = write(writer -> writer.writeItem(rust));
 
@@ -137,8 +151,7 @@ public class RustWriterTests {
         assertThat(string, equalTo("""
             #[a::b::C]
             #[derive(Debug)]
-            pub struct Rectangle {
-            }"""));
+            pub struct Rectangle;"""));
     }
 
     @Test
@@ -171,8 +184,7 @@ public class RustWriterTests {
 
         assertThat(string, equalTo("""
             /// A 2D rectangle.
-            pub struct Rectangle {
-            }"""));
+            pub struct Rectangle;"""));
     }
 
     // === Enumerations ===
diff --git a/src/test/java/org/zwobble/hobgoblin/compiler/output/lang/rust/ast/RustStructStructMatcher.java b/src/test/java/org/zwobble/hobgoblin/compiler/output/lang/rust/ast/RustStructStructMatcher.java
index b2109c1..6f04455 100644
--- a/src/test/java/org/zwobble/hobgoblin/compiler/output/lang/rust/ast/RustStructStructMatcher.java
+++ b/src/test/java/org/zwobble/hobgoblin/compiler/output/lang/rust/ast/RustStructStructMatcher.java
@@ -42,7 +42,7 @@ public class RustStructStructMatcher implements org.zwobble.precisely.Matcher<ja
         return new org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructStructMatcher(submatchers);
     }
 
-    public org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructStructMatcher withFields(org.zwobble.precisely.Matcher<? super java.util.List<org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructField>> fields) {
+    public org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructStructMatcher withFields(org.zwobble.precisely.Matcher<? super java.util.Optional<java.util.List<org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructField>>> fields) {
         var submatchers = new java.util.ArrayList<org.zwobble.precisely.Matcher<? super org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructStruct>>(this.submatchers);
         submatchers.add(org.zwobble.precisely.Matchers.has("fields", org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructStruct::fields, fields));
         return new org.zwobble.hobgoblin.compiler.output.lang.rust.ast.RustStructStructMatcher(submatchers);