Make ParserSpan noncopyable (#15)

This change helps communicate the intended usage of `ParserSpan`,
though it doesn't strictly prevent creating a copy that represents
the same memory. Specifically, the `seeking(...)` methods return
copies of the span with different boundaries, to support separate
parsing of different subregions of memory, and calling e.g.
`seeking(toRelativeOffset: 0)` returns an exact copy of the parser
span.

With a few changes inside the library to handle these explicit copies,
this change is fully source compatible with all the included example
parsers, further showing that it matches the intended usage and
semantics of the library.

Author: natecook1000

Sources/BinaryParsing/Parser Types/ParserSpan.swift

@@ -12,7 +12,7 @@
 /// A non-owning, non-escaping view for parsing binary data.
 ///
 /// You can access a `ParserSpan` from a
-public struct ParserSpan: ~Escapable, BitwiseCopyable {
+public struct ParserSpan: ~Escapable, ~Copyable {
   @usableFromInline
   var _bytes: RawSpan
   @usableFromInline
@@ -29,6 +29,14 @@ public struct ParserSpan: ~Escapable, BitwiseCopyable {
     self._upperBound = _bytes.byteCount
   }
 
+  @inlinable
+  @lifetime(copy other)
+  init(copying other: borrowing ParserSpan) {
+    self._bytes = other._bytes
+    self._lowerBound = other._lowerBound
+    self._upperBound = other._upperBound
+  }
+
   @unsafe
   @inlinable
   @lifetime(borrow buffer)
@@ -91,7 +99,7 @@ extension ParserSpan {
   mutating func divide(at index: Int) -> ParserSpan {
     precondition(index >= _lowerBound)
     precondition(index <= _upperBound)
-    var result = self
+    var result = ParserSpan(copying: self)
     result._upperBound = index
     self._lowerBound = index
     return result
@@ -193,7 +201,7 @@ extension ParserSpan {
     _ body: (inout ParserSpan) throws(E) -> T
   ) throws(E) -> T {
     // Make a mutable copy to perform the work in `body`.
-    var copy = self
+    var copy = ParserSpan(copying: self)
     let result = try body(&copy)
     // `body` didn't throw, so update `self`.
     self = copy

Sources/BinaryParsing/Parser Types/Seeking.swift

@@ -15,7 +15,7 @@ extension ParserSpan {
   public func seeking(toRange range: ParserRange)
     throws(ParsingError) -> ParserSpan
   {
-    var result = self
+    var result = ParserSpan(copying: self)
     try result.seek(toRange: range)
     return result
   }
@@ -25,7 +25,7 @@ extension ParserSpan {
   public func seeking(toRelativeOffset offset: some FixedWidthInteger)
     throws(ParsingError) -> ParserSpan
   {
-    var result = self
+    var result = ParserSpan(copying: self)
     try result.seek(toRelativeOffset: offset)
     return result
   }
@@ -35,7 +35,7 @@ extension ParserSpan {
   public func seeking(toAbsoluteOffset offset: some FixedWidthInteger)
     throws(ParsingError) -> ParserSpan
   {
-    var result = self
+    var result = ParserSpan(copying: self)
     try result.seek(toAbsoluteOffset: offset)
     return result
   }
@@ -45,7 +45,7 @@ extension ParserSpan {
   public func seeking(toOffsetFromEnd offset: some FixedWidthInteger)
     throws(ParsingError) -> ParserSpan
   {
-    var result = self
+    var result = ParserSpan(copying: self)
     try result.seek(toOffsetFromEnd: offset)
     return result
   }

Tests/BinaryParsingTests/SeekingTests.swift

@@ -61,7 +61,7 @@ struct SeekingTests {
 
       // Absolute offset is always referent to original bounds
       var slice1 = try input.sliceSpan(byteCount: 4)
-      var slice2 = slice1
+      var slice2 = try input.seeking(toRange: slice1.parserRange)
       #expect(slice1.startPosition == 2)
       #expect(slice1.count == 4)
 

Tests/BinaryParsingTests/TestingSupport.swift

@@ -14,7 +14,7 @@ import Testing
 
 /// Returns a Boolean value indicating whether two parser spans are identical,
 /// representing the same subregion of the same span of memory.
-func === (lhs: ParserSpan, rhs: ParserSpan) -> Bool {
+func === (lhs: borrowing ParserSpan, rhs: borrowing ParserSpan) -> Bool {
   guard lhs.startPosition == rhs.startPosition,
     lhs.count == rhs.count
   else { return false }