Fix ULEB encoding

Author: kastiglione

lib/Macros/Sources/SwiftMacros/DebugDescriptionMacro.swift

@@ -265,13 +265,17 @@ private func encodeString(_ string: String) -> [UInt8] {
 }
 
 private func encodeULEB(_ value: UInt) -> [UInt8] {
+    guard value > 0 else {
+        return [0]
+    }
+
     var bytes: [UInt8] = []
     var buffer = value
     while buffer > 0 {
         var byte = UInt8(buffer & 0b01111111)
         buffer >>= 7
         if buffer > 0 {
-            byte &= 0b1000000
+            byte |= 0b10000000
         }
         bytes.append(byte)
     }

test/Macros/DebugDescription/long_string.swift

@@ -0,0 +1,25 @@
+// REQUIRES: swift_swift_parser
+
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend %s -swift-version 5 -module-name main -typecheck -enable-experimental-feature SymbolLinkageMarkers -plugin-path %swift-plugin-dir -dump-macro-expansions > %t/expansions-dump.txt 2>&1
+// RUN: %FileCheck %s < %t/expansions-dump.txt
+
+@attached(peer, names: suffixed(_lldb_summary))
+public macro _DebugDescription() =
+  #externalMacro(module: "SwiftMacros", type: "DebugDescriptionMacro")
+
+@_DebugDescription
+struct MyStruct: CustomDebugStringConvertible {
+  var debugDescription: String {
+    """
+    A string longer than one hundred and twenty eight characters, for the purpose of
+    testing Unsigned Little Endian encoding (ULEB). Values less than or equal to 127 are
+    represented as a single byte, with a bit representation identical to an unsigned
+    8-bit integer. See https://en.wikipedia.org/wiki/LEB128
+    """
+  }
+}
+// CHECK: let MyStruct_lldb_summary = (
+// CHECK:     /* version */ 1 as UInt8,
+// CHECK:     /* record size */ 192 as UInt8, 2 as UInt8,
+// CHECK: 8-bit integer. See https://en.wikipedia.org/wiki/LEB128" */ 175 as UInt8, 2 as UInt8, 65 as UInt8,