[wpiutil] Add remove_prefix() and remove_suffix() (#6118)

wpiutil/src/main/native/thirdparty/llvm/cpp/llvm/StringExtras.cpp

@@ -278,7 +278,7 @@ bool wpi::detail::ConsumeSignedInteger(
   }
 
   // Get the positive part of the value.
-  std::string_view str2 = wpi::drop_front(str, 1);
+  std::string_view str2 = wpi::drop_front(str);
   if (wpi::detail::ConsumeUnsignedInteger(str2, radix, ullVal) ||
       // Reject values so large they'd overflow as negative signed, but allow
       // "-0".  This negates the unsigned so that the negative isn't undefined

wpiutil/src/main/native/thirdparty/llvm/include/wpi/StringExtras.h

@@ -357,6 +357,32 @@ inline bool contains_lower(std::string_view str, const char* other) noexcept {
   return find_lower(str, other) != std::string_view::npos;
 }
 
+/**
+ * Return an optional containing @p str but with @p prefix removed if the string
+ * starts with the prefix. If the string does not start with the prefix, return
+ * an empty optional.
+ */
+constexpr std::optional<std::string_view> remove_prefix(std::string_view str, std::string_view prefix) noexcept {
+  if (str.starts_with(prefix)) {
+    str.remove_prefix(prefix.size());
+    return str;
+  }
+  return std::nullopt;
+}
+
+/**
+ * Return an optional containing @p str but with @p suffix removed if the
+ * string ends with the suffix. If the string does not end with the suffix,
+ * return an empty optional.
+ */
+constexpr std::optional<std::string_view> remove_suffix(std::string_view str, std::string_view suffix) noexcept {
+  if (str.ends_with(suffix)) {
+    str.remove_suffix(suffix.size());
+    return str;
+  }
+  return std::nullopt;
+}
+
 /**
  * Return a string_view equal to @p str but with the first @p n elements
  * dropped.