sql: fix cast from string to array with width

The code that performs a cast from string to array doesn't take into
account the width of the string type it is producing. This doesn't
show up when the input is a literal constant because the constant is
first parsed as an array of (vanilla) strings which is then subjected
to a cast (to array of strings with width).

Fixes #50132.

Release note (bug fix): Fixed some cases where casting a string to a
width-limited string array was not truncating the string.

pkg/sql/logictest/testdata/logic_test/array

@@ -173,6 +173,17 @@ SELECT '{hello, a🐛b🏠c}'::VARCHAR(2)[]
 ----
 {he,a🐛}
 
+# Regression test for #50132.
+statement ok
+CREATE TABLE hello (s STRING);
+INSERT INTO hello VALUES ('{hello}'), ('{hello,a🐛b🏠c}')
+
+query T rowsort
+SELECT s::VARCHAR(2)[] FROM hello
+----
+{he}
+{he,a🐛}
+
 # array casting
 
 query T

pkg/sql/sem/tree/parse_string.go

@@ -12,6 +12,7 @@ package tree
 
 import (
 	"github.com/cockroachdb/cockroach/pkg/sql/types"
+	"github.com/cockroachdb/cockroach/pkg/util"
 	"github.com/cockroachdb/errors"
 )
 
@@ -49,6 +50,12 @@ func ParseAndRequireString(t *types.T, s string, ctx ParseTimeContext) (Datum, e
 		i, err := ParseDInt(s)
 		return NewDOid(*i), err
 	case types.StringFamily:
+		// If the string type specifies a limit we truncate to that limit:
+		//   'hello'::CHAR(2) -> 'he'
+		// This is true of all the string type variants.
+		if t.Width() > 0 {
+			s = util.TruncateString(s, int(t.Width()))
+		}
 		return NewDString(s), nil
 	case types.TimeFamily:
 		return ParseDTime(ctx, s, TimeFamilyPrecisionToRoundDuration(t.Precision()))

pkg/sql/sem/tree/testdata/eval/cast

@@ -1070,3 +1070,14 @@ eval
 '-10'::interval::decimal
 ----
 -10.000000000
+
+eval
+'{hello,a🐛b🏠c}'::VARCHAR(2)[]
+----
+ARRAY['he',e'a\U0001F41B']
+
+# Test the same cast, but not with a literal constant (see #50132).
+eval
+('{he' || ',a🐛b🏠}')::VARCHAR(2)[]
+----
+ARRAY['he',e'a\U0001F41B']