Add build for platform function.

sketching/may_2025/print.dm

@@ -0,0 +1,5 @@
+ns std::core;
+
+platform fn print(msg: Any) -> Void;
+
+platform fn println(msg: Any) -> Void;

src/ast/build.rs

@@ -594,7 +594,46 @@ fn build_platform_function_declaration(
     file_id: usize,
     platform_function_pair: Pair<Rule>,
 ) -> PlatformFunctionDeclaration {
-    todo!()
+    let mut is_public = false;
+    let mut modifier = None;
+    let mut generics = GenericParameters::default();
+    let mut identifier = None;
+    let mut parameters = Parameters::default();
+    let mut return_type = None;
+    
+    for inner_pair in platform_function_pair.into_inner() {
+        match inner_pair.as_rule() {
+            Rule::Pub => {
+                is_public = true;
+            }
+            Rule::FunctionModifier => {
+                modifier = Some(build_function_modifier(file_id, inner_pair));
+            }
+            Rule::Platform | Rule::Fn => {},
+            Rule::GenericParameters => {
+                generics = build_generic_parameters(file_id, inner_pair);
+            }
+            Rule::Identifier => {
+                identifier = Some(build_identifier(file_id, inner_pair));
+            }
+            Rule::Parameters => {
+                parameters = build_parameters(file_id, inner_pair);
+            }
+            Rule::ReturnType => {
+                return_type = Some(build_return_type(file_id, inner_pair));
+            }
+            _ => unreachable!(),
+        }
+    }
+    
+    PlatformFunctionDeclaration {
+        is_public,
+        modifier,
+        generics,
+        identifier: identifier.unwrap(),
+        parameters,
+        return_type: return_type.unwrap(),
+    }
 }
 
 fn build_interface_function_declaration(
@@ -1798,4 +1837,9 @@ mod tests {
     fn use_list() {
         assert_builds("use std::core::{print, println};");
     }
+    
+    #[test]
+    fn platform_function() {
+        assert_builds("platform fn println(msg: Any) -> Void;");
+    }
 }

src/ast/unparse.rs

@@ -574,6 +574,7 @@ impl Unparse for PlatformFunctionDeclaration {
         self.parameters.unparse(writer)?;
         writer.write(" ")?;
         self.return_type.unparse(writer)?;
+        writer.write(";")?;
         Ok(())
     }
 }

src/name_analysis/mod.rs

@@ -90,7 +90,7 @@ mod tests {
             let file_id = files.add(file_name, source);
             let parse_result = DeimosParser::parse(Rule::CompilationUnit, source);
             if let Err(err) = &parse_result {
-                panic!("{:?}", err);
+                panic!("{}", err);
             }
             let mut pairs = parse_result.unwrap();
             if pairs.as_str().trim() != source.trim() {
@@ -148,7 +148,7 @@ mod tests {
                 indoc! {"
                 ns std::core;
 
-                declare platform fn println(msg: String) -> Void
+                platform fn println(msg: String) -> Void;
             "},
             ),
         ]);

src/parser/deimos.pest

@@ -385,6 +385,7 @@ PlatformFunction = {
     ~ Identifier
     ~ Parameters
     ~ ReturnType
+    ~ ";"
 }
 
 InterfaceFunction = {