[Wasm] Add comments to .wat files

wasm/wasm.ir/src/org/jetbrains/kotlin/wasm/ir/Operators.kt

@@ -95,6 +95,9 @@ sealed class WasmImmediate {
     class HeapType(val value: WasmHeapType) : WasmImmediate() {
         constructor(type: WasmType) : this(type.getHeapType())
     }
+
+    // Pseudo-immediates
+    class ConstString(val value: String) : WasmImmediate()
 }
 
 
@@ -403,11 +406,17 @@ enum class WasmOp(
 
     // ============================================================
     // Pseudo-instruction, just alias for a normal call. It's used to easily spot get_unit on the wasm level.
-    GET_UNIT("call", 0x10, FUNC_IDX)
+    GET_UNIT("call", 0x10, FUNC_IDX),
+
+    PSEUDO_COMMENT_PREVIOUS_INSTR("<comment-single>", WASM_OP_PSEUDO_OPCODE),
+    PSEUDO_COMMENT_GROUP_START("<comment-group-start>", WASM_OP_PSEUDO_OPCODE),
+    PSEUDO_COMMENT_GROUP_END("<comment-group-end>", WASM_OP_PSEUDO_OPCODE),
     ;
 
     constructor(mnemonic: String, opcode: Int, vararg immediates: WasmImmediateKind) : this(mnemonic, opcode, immediates.toList())
 }
 
+const val WASM_OP_PSEUDO_OPCODE = 0xFFFF
+
 val opcodesToOp: Map<Int, WasmOp> =
     enumValues<WasmOp>().associateBy { it.opcode }

wasm/wasm.ir/src/org/jetbrains/kotlin/wasm/ir/WasmExpressionBuilder.kt

@@ -178,4 +178,16 @@ abstract class WasmExpressionBuilder {
     fun buildDrop() {
         buildInstr(WasmOp.DROP)
     }
+
+    inline fun commentPreviousInstr(text: () -> String) {
+        buildInstr(WasmOp.PSEUDO_COMMENT_PREVIOUS_INSTR, WasmImmediate.ConstString(text()))
+    }
+
+    inline fun commentGroupStart(text: () -> String) {
+        buildInstr(WasmOp.PSEUDO_COMMENT_GROUP_START, WasmImmediate.ConstString(text()))
+    }
+
+    fun commentGroupEnd() {
+        buildInstr(WasmOp.PSEUDO_COMMENT_GROUP_END)
+    }
 }

wasm/wasm.ir/src/org/jetbrains/kotlin/wasm/ir/convertors/WasmIrToBinary.kt

@@ -210,6 +210,10 @@ class WasmIrToBinary(
         }
 
         val opcode = instr.operator.opcode
+
+        if (opcode == WASM_OP_PSEUDO_OPCODE)
+            return
+
         if (opcode > 0xFF) {
             b.writeByte((opcode ushr 8).toByte())
             b.writeByte((opcode and 0xFF).toByte())
@@ -259,6 +263,8 @@ class WasmIrToBinary(
             is WasmImmediate.GcType -> appendModuleFieldReference(x.value.owner)
             is WasmImmediate.StructFieldIdx -> b.writeVarUInt32(x.value.owner)
             is WasmImmediate.HeapType -> appendHeapType(x.value)
+            is WasmImmediate.ConstString ->
+                error("Instructions with pseudo immediates should be skipped")
         }
     }
 

wasm/wasm.ir/src/org/jetbrains/kotlin/wasm/ir/convertors/WasmIrToText.kt

@@ -60,6 +60,34 @@ class WasmIrToText : SExpressionBuilder() {
 
     private fun appendInstr(wasmInstr: WasmInstr) {
         val op = wasmInstr.operator
+
+        if (op.opcode == WASM_OP_PSEUDO_OPCODE) {
+            fun commentText() =
+                (wasmInstr.immediates.single() as WasmImmediate.ConstString).value
+
+            when (op) {
+                WasmOp.PSEUDO_COMMENT_PREVIOUS_INSTR -> {
+                    val text = commentText()
+                    require(text.lineSequence().count() < 2) { "Comments for single instruction should be in one line" }
+                    stringBuilder.append("  ;; ")
+                    stringBuilder.append(text)
+                }
+                WasmOp.PSEUDO_COMMENT_GROUP_START -> {
+                    newLine()
+                    commentText().lines().forEach { line ->
+                        newLine()
+                        stringBuilder.append(";; ")
+                        stringBuilder.append(line)
+                    }
+                }
+                WasmOp.PSEUDO_COMMENT_GROUP_END -> {
+                    newLine()
+                }
+                else -> error("Unknown pseudo op $op")
+            }
+            return
+        }
+
         if (op == WasmOp.END || op == WasmOp.ELSE || op == WasmOp.CATCH)
             indent--
 
@@ -113,6 +141,8 @@ class WasmIrToText : SExpressionBuilder() {
             is WasmImmediate.HeapType -> {
                 appendHeapType(x.value)
             }
+
+            is WasmImmediate.ConstString -> error("Pseudo immediate")
         }
     }