Catch an unchecked exception which may be thrown by Strings.repeat()

To provide a nicer error message for the user. Otherwise, we'd get an
UncheckedEvalException without a Starlark stack trace.

RELNOTES: None.
PiperOrigin-RevId: 384559307

src/main/java/net/starlark/java/eval/EvalUtils.java

@@ -391,8 +391,15 @@ private static int compare(Object x, Object y) throws EvalException {
 
   private static String repeatString(String s, StarlarkInt in) throws EvalException {
     int n = in.toInt("repeat");
-    // TODO(adonovan): reject unreasonably large n.
-    return n <= 0 ? "" : Strings.repeat(s, n);
+    if (n <= 0) {
+      return "";
+    } else if ((long) s.length() * (long) n > Integer.MAX_VALUE) {
+      // Would exceed max length of a java String (and would cause an undocumented
+      // ArrayIndexOutOfBoundsException to be thrown in Strings.repeat()).
+      throw Starlark.errorf("excessive repeat (%d * %d characters)", s.length(), n);
+    } else {
+      return Strings.repeat(s, n);
+    }
   }
 
   /** Evaluates a unary operation. */

src/test/java/net/starlark/java/eval/testdata/list.star

@@ -63,3 +63,4 @@ assert_eq(3 * [1, 2, 3], [1, 2, 3, 1, 2, 3, 1, 2, 3])
 assert_eq([1, 2, 3] * -1, [])
 assert_eq([1, 2, 3] * 0, [])
 assert_fails(lambda: [1] * (1 << 35), "got 34359738368 for repeat, want value in signed 32-bit range")
+assert_fails(lambda: [1, 2, 3] * (1 << 30), "excessive repeat \\(3 \\* 1073741824 elements\\)")

src/test/java/net/starlark/java/eval/testdata/string_misc.star

@@ -176,3 +176,4 @@ assert_eq(3 * "abc", "abcabcabc")
 assert_eq("abc" * 0, "")
 assert_eq("abc" * -1, "")
 assert_fails(lambda: "abc" * (1 << 35), "got 34359738368 for repeat, want value in signed 32-bit range")
+assert_fails(lambda: "abc" * (1 << 30), "excessive repeat \\(3 \\* 1073741824 characters\\)")