WasmParser: Add ExpressionParser API

Author: kateinoigakukun

Sources/WasmKit/Translator.swift

@@ -344,22 +344,22 @@ struct InstructionTranslator<Context: TranslatorContext>: InstructionVisitor {
 
         private mutating func setReachability(_ value: Bool) throws {
             guard !self.frames.isEmpty else {
-                throw TranslationError("Control stack is empty. Instruction cannot be appeared after \"end\" of function")
+                throw ValidationError("Control stack is empty. Instruction cannot be appeared after \"end\" of function")
             }
             self.frames[self.frames.count - 1].reachable = value
         }
 
         func currentFrame() throws -> ControlFrame {
             guard let frame = self.frames.last else {
-                throw TranslationError("Control stack is empty. Instruction cannot be appeared after \"end\" of function")
+                throw ValidationError("Control stack is empty. Instruction cannot be appeared after \"end\" of function")
             }
             return frame
         }
 
         func branchTarget(relativeDepth: UInt32) throws -> ControlFrame {
             let index = frames.count - 1 - Int(relativeDepth)
             guard frames.indices.contains(index) else {
-                throw TranslationError("Relative depth \(relativeDepth) is out of range")
+                throw ValidationError("Relative depth \(relativeDepth) is out of range")
             }
             return frames[index]
         }
@@ -1062,7 +1062,16 @@ struct InstructionTranslator<Context: TranslatorContext>: InstructionVisitor {
             // Emit `onEnter` instruction at the beginning of the function
             emit(.onEnter(functionIndex))
         }
-        try code.parseExpression(visitor: &self)
+        var parser = ExpressionParser(code: code)
+        var offset = parser.offset
+        do {
+            while try parser.visit(visitor: &self) {
+                offset = parser.offset
+            }
+        } catch var error as ValidationError {
+            error.offset = offset
+            throw error
+        }
         return try finalize()
     }
 

Sources/WasmKit/Validator.swift

@@ -1,10 +1,19 @@
 import WasmParser
 
 struct ValidationError: Error, CustomStringConvertible {
-    let description: String
+    let message: String
+    var offset: Int?
 
-    init(_ description: String) {
-        self.description = description
+    var description: String {
+        if let offset = offset {
+            return "\(message) at offset 0x\(String(offset, radix: 16))"
+        } else {
+            return message
+        }
+    }
+
+    init(_ message: String) {
+        self.message = message
     }
 }
 

Sources/WasmParser/WasmParser.swift

@@ -126,6 +126,39 @@ extension Code {
     }
 }
 
+// TODO: Move `doParseInstruction` under `ExpressionParser` struct
+@_documentation(visibility: internal)
+public struct ExpressionParser {
+    @usableFromInline
+    let parser: Parser<StaticByteStream>
+    @usableFromInline
+    var lastCode: InstructionCode?
+
+    public var offset: Int {
+        self.parser.currentIndex
+    }
+
+    public init(code: Code) {
+        self.parser = Parser(
+            stream: StaticByteStream(bytes: code.expression),
+            features: code.features,
+            hasDataCount: code.hasDataCount
+        )
+    }
+
+    @inlinable
+    public mutating func visit<V: InstructionVisitor>(visitor: inout V) throws -> Bool {
+        lastCode = try parser.parseInstruction(visitor: &visitor)
+        let shouldContinue = try !parser.stream.hasReachedEnd()
+        if !shouldContinue {
+            guard lastCode == .end else {
+                throw WasmParserError.endOpcodeExpected
+            }
+        }
+        return shouldContinue
+    }
+}
+
 /// Flags for enabling/disabling WebAssembly features
 public struct WasmFeatureSet: OptionSet {
     /// The raw value of the feature set