Issue 6378 - [emscripten] Make DependentString constexpr

compiled/String.h

Index: compiled/String.h
diff --git a/compiled/String.h b/compiled/String.h
index 901602d882889a52491ba0f4cd1e66cbaf48b180..62fcd9b5e1eea8064c6678f606d7c6cdf2cd1ffb 100644
--- a/compiled/String.h
+++ b/compiled/String.h
@@ -61,14 +61,12 @@ protected:
   value_type* mBuf;
   size_type mLen;
 
-  explicit String(value_type* buf, size_type len, size_type flags)
+  constexpr explicit String(value_type* buf, size_type len, size_type flags)
       : mBuf(buf), mLen((len & LENGTH_MASK) | flags)
   {
   }
 
-  ~String()
-  {
-  }
+  ~String() = default;
 
   void reset(value_type* buf, size_type len, size_type flags)
   {
@@ -77,17 +75,17 @@ protected:
   }
 
 public:
-  size_type length() const
+  constexpr size_type length() const
   {
     return mLen & LENGTH_MASK;
   }
 
-  bool empty() const
+  constexpr bool empty() const
   {
     return !(mLen & LENGTH_MASK);
   }
 
-  const value_type* data() const
+  constexpr const value_type* data() const
   {
     return mBuf;
   }
@@ -98,7 +96,7 @@ public:
     return mBuf;
   }
 
-  const value_type& operator[](size_type pos) const
+  constexpr const value_type& operator[](size_type pos) const
   {
     return mBuf[pos];
   }
@@ -109,7 +107,7 @@ public:
     return mBuf[pos];
   }
 
-  bool is_writable() const
+  constexpr bool is_writable() const
   {
     return (mLen & FLAGS_MASK) == READ_WRITE;
   }
@@ -179,12 +177,12 @@ public:
     return npos;
   }
 
-  bool is_invalid() const
+  constexpr bool is_invalid() const
   {
     return (mLen & FLAGS_MASK) == INVALID;
   }
 
-  bool is_deleted() const
+  constexpr bool is_deleted() const
   {
     return (mLen & FLAGS_MASK) == DELETED;
   }
@@ -226,11 +224,17 @@ inline std::ostream& operator<<(std::ostream& os, const String& str)
 class DependentString : public String
 {
 public:
-  explicit DependentString()
+  constexpr explicit DependentString()
       : String(nullptr, 0, INVALID)
   {
   }
 
+  template <int N1>
+  constexpr explicit DependentString(const value_type (&buf)[N1])
+      : String(const_cast<value_type*>(buf), N1 - 1, READ_ONLY)
+  {
+  }
+
   explicit DependentString(value_type* buf, size_type len)
       : String(buf, len, READ_WRITE)
   {