From 281dc0fba176df22fc35ff5f5acb7a05863b9d59 Mon Sep 17 00:00:00 2001
From: Richard Tia <richie.tia@gmail.com>
Date: Fri, 21 Jul 2023 08:59:07 -0700
Subject: [PATCH] feat: add options to substring for start parameter being
 negative (#508)

The substring function `start` parameter has different behavior between
different
backends when it's value negative. Sqlite will wrap around the end of
the input string,
whereas postgres will start from the left of the input string.
---
 extensions/functions_string.yaml | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/extensions/functions_string.yaml b/extensions/functions_string.yaml
index 7842e94eb..159988c47 100644
--- a/extensions/functions_string.yaml
+++ b/extensions/functions_string.yaml
@@ -53,6 +53,13 @@ scalar_functions:
       A `start` value of 1 refers to the first characters of the string.  When
       `length` is not specified the function will extract a substring starting
       from position `start` and ending at the end of the string.
+
+      The `negative_start` option applies to the `start` parameter. `WRAP_FROM_END` means
+      the index will start from the end of the `input` and move backwards.
+      The last character has an index of -1, the second to last character has an index of -2,
+      and so on. `LEFT_OF_BEGINNING` means the returned substring will start from
+      the left of the first character.  A `start` of -1 will begin 2 characters left of the
+      the `input`, while a `start` of 0 begins 1 character left of the `input`.
     impls:
       - args:
           - value: "varchar<L1>"
@@ -61,6 +68,9 @@ scalar_functions:
             name: "start"
           - value: i32
             name: "length"
+        options:
+          negative_start:
+            values: [ WRAP_FROM_END, LEFT_OF_BEGINNING, ERROR ]
         return: "varchar<L1>"
       - args:
           - value: "string"
@@ -69,6 +79,9 @@ scalar_functions:
             name: "start"
           - value: i32
             name: "length"
+        options:
+          negative_start:
+            values: [ WRAP_FROM_END, LEFT_OF_BEGINNING, ERROR ]
         return: "string"
       - args:
           - value: "fixedchar<l1>"
@@ -77,24 +90,36 @@ scalar_functions:
             name: "start"
           - value: i32
             name: "length"
+        options:
+          negative_start:
+            values: [ WRAP_FROM_END, LEFT_OF_BEGINNING, ERROR ]
         return: "string"
       - args:
           - value: "varchar<L1>"
             name: "input"
           - value: i32
             name: "start"
+        options:
+          negative_start:
+            values: [ WRAP_FROM_END, LEFT_OF_BEGINNING ]
         return: "varchar<L1>"
       - args:
           - value: "string"
             name: "input"
           - value: i32
             name: "start"
+        options:
+          negative_start:
+            values: [ WRAP_FROM_END, LEFT_OF_BEGINNING ]
         return: "string"
       - args:
           - value: "fixedchar<l1>"
             name: "input"
           - value: i32
             name: "start"
+        options:
+          negative_start:
+            values: [ WRAP_FROM_END, LEFT_OF_BEGINNING ]
         return: "string"
   -
     name: regexp_match_substring