[KT-63275] Implement trivial bodies in SIR functions

native/swift/sir-printer/src/org/jetbrains/sir/printer/SirAsSwiftSourcesPrinter.kt

@@ -78,7 +78,7 @@ public class SirAsSwiftSourcesPrinter(private val printer: SmartPrinter) : SirVi
 }
 
 private fun printFunctionBody(function: SirFunction): List<String> {
-    return listOf("fatalError()")
+    return function.body?.statements ?: listOf("fatalError()")
 }
 
 private val SirVisibility.swift

native/swift/sir-printer/testData/non_empty_body.golden.swift

@@ -0,0 +1,5 @@
+public func foo(
+    arg1: Swift.Int32
+) -> Swift.Bool {
+    return foo_wrapped(arg1)
+}

native/swift/sir-printer/tests/org/jetbrains/kotlin/sir/printer/SirAsSwiftSourcesPrinterTests.kt

@@ -191,6 +191,34 @@ class SirAsSwiftSourcesPrinterTests {
         )
     }
 
+    @Test
+    fun `should print non-empty bodies`() {
+
+        val module = buildModule {
+            name = "Test"
+            declarations.add(
+                buildFunction {
+                    origin = SirOrigin.Unknown
+                    visibility = SirVisibility.PUBLIC
+                    name = "foo"
+                    parameters.add(
+                        SirParameter(
+                            argumentName = "arg1",
+                            type = SirNominalType(SirSwiftModule.int32)
+                        )
+                    )
+                    returnType = SirNominalType(SirSwiftModule.bool)
+                    body = SirFunctionBody(listOf("return foo_wrapped(arg1)"))
+                }
+            )
+        }
+
+        runTest(
+            module,
+            "testData/non_empty_body"
+        )
+    }
+
     private fun runTest(module: SirModule, goldenDataFile: String) {
         val expectedSwiftSrc = File(KtTestUtil.getHomeDirectory()).resolve("$goldenDataFile.golden.swift")
 

native/swift/sir/src/org/jetbrains/kotlin/sir/SirFunctionBody.kt

@@ -5,5 +5,10 @@
 
 package org.jetbrains.kotlin.sir
 
-class SirFunctionBody {
-}
+/**
+ * A body of a SIR function.
+ *
+ * For now, it is just a list of statements. This is sufficient as bodies are pretty trivial.
+ * In the future, it may become more complicated as bridging logic becomes more sophisticated.
+ */
+class SirFunctionBody(val statements: List<String>)