builtins: change concat_ws() to accept arguments of types.Any type

Previously, concat_ws() required all arguments to be of type string,
this patch changes the requirement such that the first argument (the
delimiter) must be a string but that all follow-on arguments may be of
any type.

Release note (sql change): concat_ws() now accepts arguments of any type
in the second and later positions (the separator must still be a
string).

Author: mw5h

docs/generated/sql/functions.md

@@ -2914,7 +2914,7 @@ Can be used to define the tile bounds required by ST_AsMVTGeom to convert geomet
 </span></td><td>Immutable</td></tr>
 <tr><td><a name="concat"></a><code>concat(any...) &rarr; <a href="string.html">string</a></code></td><td><span class="funcdesc"><p>Concatenates a comma-separated list of strings.</p>
 </span></td><td>Immutable</td></tr>
-<tr><td><a name="concat_ws"></a><code>concat_ws(<a href="string.html">string</a>...) &rarr; <a href="string.html">string</a></code></td><td><span class="funcdesc"><p>Uses the first argument as a separator between the concatenation of the subsequent arguments.</p>
+<tr><td><a name="concat_ws"></a><code>concat_ws(<a href="string.html">string</a>, any...) &rarr; <a href="string.html">string</a></code></td><td><span class="funcdesc"><p>Uses the first argument as a separator between the concatenation of the subsequent arguments.</p>
 <p>For example <code>concat_ws('!','wow','great')</code> returns <code>wow!great</code>.</p>
 </span></td><td>Immutable</td></tr>
 <tr><td><a name="convert_from"></a><code>convert_from(str: <a href="bytes.html">bytes</a>, enc: <a href="string.html">string</a>) &rarr; <a href="string.html">string</a></code></td><td><span class="funcdesc"><p>Decode the bytes in <code>str</code> into a string using encoding <code>enc</code>. Supports encodings ‘UTF8’ and ‘LATIN1’.</p>

pkg/sql/logictest/testdata/logic_test/builtin_function

@@ -428,8 +428,10 @@ SELECT concat_ws(',', 'abcde', '2')
 ----
 abcde,2
 
-statement error unknown signature: concat_ws\(string, string, int, unknown, int\)
+query T
 SELECT concat_ws(',', 'abcde', 2, NULL, 22)
+----
+abcde,2,22
 
 query T
 SELECT split_part('abc~@~def~@~ghi', '~@~', 2)

pkg/sql/sem/builtins/builtins.go

@@ -472,7 +472,7 @@ var regularBuiltins = map[string]builtinDefinition{
 	"concat_ws": makeBuiltin(
 		defProps(),
 		tree.Overload{
-			Types:      tree.VariadicType{VarType: types.String},
+			Types:      tree.VariadicType{FixedTypes: []*types.T{types.String}, VarType: types.Any},
 			ReturnType: tree.FixedReturnType(types.String),
 			Fn: func(_ context.Context, _ *eval.Context, args tree.Datums) (tree.Datum, error) {
 				if len(args) == 0 {
@@ -481,25 +481,24 @@ var regularBuiltins = map[string]builtinDefinition{
 				if args[0] == tree.DNull {
 					return tree.DNull, nil
 				}
-				sep := string(tree.MustBeDString(args[0]))
-				var buf bytes.Buffer
-				prefix := ""
-				length := 0
+				sep := tree.MustBeDString(args[0])
+				ctx := tree.NewFmtCtx(tree.FmtPgwireText)
+				prefix := false
 				for _, d := range args[1:] {
 					if d == tree.DNull {
 						continue
 					}
-					length += len(prefix) + len(string(tree.MustBeDString(d)))
-					if length > builtinconstants.MaxAllocatedStringSize {
+					if ctx.Buffer.Len()+int(d.Size())+int(sep.Size()) > builtinconstants.MaxAllocatedStringSize {
 						return nil, errStringTooLarge
 					}
-					// Note: we can't use the range index here because that
-					// would break when the 2nd argument is NULL.
-					buf.WriteString(prefix)
-					prefix = sep
-					buf.WriteString(string(tree.MustBeDString(d)))
+					if prefix {
+						sep.Format(ctx)
+					} else {
+						prefix = true
+					}
+					d.Format(ctx)
 				}
-				return tree.NewDString(buf.String()), nil
+				return tree.NewDString(ctx.CloseAndGetString()), nil
 			},
 			Info: "Uses the first argument as a separator between the concatenation of the " +
 				"subsequent arguments. \n\nFor example `concat_ws('!','wow','great')` " +

pkg/sql/sem/builtins/fixed_oids.go

@@ -822,7 +822,7 @@ var builtinOidsArray = []string{
 	846:  `substring(input: bytes, start_pos: int) -> bytes`,
 	847:  `substring(input: bytes, start_pos: int, length: int) -> bytes`,
 	848:  `concat(any...) -> string`,
-	849:  `concat_ws(string...) -> string`,
+	849:  `concat_ws(string, any...) -> string`,
 	850:  `convert_from(str: bytes, enc: string) -> string`,
 	851:  `convert_to(str: string, enc: string) -> bytes`,
 	852:  `get_bit(bit_string: varbit, index: int) -> int`,