Panic on adding a foreign key constraint

[VinaiRachakonda]

Consider the following dump

DROP TABLE IF EXISTS `a`;
CREATE TABLE `a` (
  `id` int NOT NULL AUTO_INCREMENT,
  `a` text NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
INSERT INTO `a` (`id`,`a`) VALUES (1,'a');
DROP TABLE IF EXISTS `b`;
CREATE TABLE `b` (
  `id` int NOT NULL AUTO_INCREMENT,
  `b` text NOT NULL,
  `a_id` int,
  PRIMARY KEY (`id`),
  KEY `b_a_id` (`a_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
INSERT INTO `b` (`id`,`b`,`a_id`) VALUES (1,'b',NULL);
INSERT INTO `b` (`id`,`b`,`a_id`) VALUES (2,'b2',31337);
INSERT INTO `b` (`id`,`b`,`a_id`) VALUES (3,'b2',31337);
INSERT INTO `b` (`id`,`b`,`a_id`) VALUES (4,'b2',31337);

The following query causes a panic

ALTER TABLE `b` ADD CONSTRAINT `fk_b_a_id_refs_a` FOREIGN KEY (`a_id`) REFERENCES `a` (`id`);

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x18 pc=0x16b6fdc]

goroutine 1 [running]:
github.com/dolthub/dolt/go/store/types.newSequenceImpl(...)
	/Users/vinairachakonda/go/src/dolthub/dolt/go/store/types/sequence.go:75
github.com/dolthub/dolt/go/store/types.newLeafSequence({0x0, 0x0}, {0xc000a6a38a, 0x5, 0x2e}, {0xc0006c6c80, 0x5, 0x8}, 0x2)
	/Users/vinairachakonda/go/src/dolthub/dolt/go/store/types/leaf_sequence.go:36 +0x7c
github.com/dolthub/dolt/go/store/types.(*valueDecoder).readSequence(0xc000a25480, 0xc0004fa640, 0x1, 0xc000530210)
	/Users/vinairachakonda/go/src/dolthub/dolt/go/store/types/value_decoder.go:179 +0x3ad
github.com/dolthub/dolt/go/store/types.(*valueDecoder).readBlobSequence(0xfd5, 0x100e625)
	/Users/vinairachakonda/go/src/dolthub/dolt/go/store/types/value_decoder.go:183 +0x4c
github.com/dolthub/dolt/go/store/types.(*valueDecoder).readValue(0xc000a25480, 0xc000a25440)
	/Users/vinairachakonda/go/src/dolthub/dolt/go/store/types/value_decoder.go:321 +0x116
github.com/dolthub/dolt/go/store/types.(*TupleIterator).Next(0xc00069ada0)
	/Users/vinairachakonda/go/src/dolthub/dolt/go/store/types/tuple.go:125 +0x3e
github.com/dolthub/dolt/go/store/types.Tuple.IterFields({{{0x0, 0x0}, 0x3a66710, {0xc000a6a380, 0x16, 0x38}, {0x0, 0x0, 0x0}}}, 0xc000530940)
	/Users/vinairachakonda/go/src/dolthub/dolt/go/store/types/tuple.go:537 +0x1af
github.com/dolthub/dolt/go/store/types.(*hrsWriter).Write(0xc000a25440, {0x2b83e00, 0xc00019a000}, {0x2bc8900, 0xc000a67680})
	/Users/vinairachakonda/go/src/dolthub/dolt/go/store/types/encode_human_readable.go:236 +0xd8c
github.com/dolthub/dolt/go/store/types.encodedValueFormat({0x2b83e00, 0xc00019a000}, {0x2bc8900, 0xc000a67680}, 0x67)
	/Users/vinairachakonda/go/src/dolthub/dolt/go/store/types/encode_human_readable.go:545 +0xa5
github.com/dolthub/dolt/go/store/types.EncodedValue(...)
	/Users/vinairachakonda/go/src/dolthub/dolt/go/store/types/encode_human_readable.go:564
github.com/dolthub/dolt/go/libraries/doltcore/doltdb.(*ForeignKeyViolationError).Error(0xc000d36540)
	/Users/vinairachakonda/go/src/dolthub/dolt/go/libraries/doltcore/doltdb/foreign_key_coll.go:66 +0x4ef
github.com/dolthub/dolt/go/cmd/dolt/errhand.VerboseErrorFromError({0x2b4c0c0, 0xc000d36540})
	/Users/vinairachakonda/go/src/dolthub/dolt/go/cmd/dolt/errhand/derr.go:119 +0x62
github.com/dolthub/dolt/go/cmd/dolt/commands.formatQueryError({0x0, 0xc0006587e0}, {0x2b4c0c0, 0xc000d36540})
	/Users/vinairachakonda/go/src/dolthub/dolt/go/cmd/dolt/commands/sql.go:536 +0x3a8
github.com/dolthub/dolt/go/cmd/dolt/commands.runShell.func3.1({0x2b83e70, 0xc00002a6f0}, 0xc0000ec8a0, 0xc0008e40a0, 0xc000114620, 0xc000120000, {0xc0006587e0, 0x5c}, 0xc000531268, 0xc000531228, ...)
	/Users/vinairachakonda/go/src/dolthub/dolt/go/cmd/dolt/commands/sql.go:840 +0x43b
github.com/dolthub/dolt/go/cmd/dolt/commands.runShell.func3(0xc000120000)
	/Users/vinairachakonda/go/src/dolthub/dolt/go/cmd/dolt/commands/sql.go:851 +0x48c
github.com/dolthub/ishell.handleUninterpretedInput(0xc000120000, {0xc0006587e0, 0x1})
	/Users/vinairachakonda/go/pkg/mod/github.com/dolthub/ishell@v0.0.0-20220112232610-14e753f0f371/ishell.go:288 +0x144
github.com/dolthub/ishell.(*Shell).run(0xc000120000)
	/Users/vinairachakonda/go/pkg/mod/github.com/dolthub/ishell@v0.0.0-20220112232610-14e753f0f371/ishell.go:245 +0x326
github.com/dolthub/ishell.(*Shell).Run(0xc000120000)
	/Users/vinairachakonda/go/pkg/mod/github.com/dolthub/ishell@v0.0.0-20220112232610-14e753f0f371/ishell.go:139 +0x28
github.com/dolthub/dolt/go/cmd/dolt/commands.runShell({0x2b83e70, 0xc00002a6f0}, 0xc0000ec8a0, 0x2b83e70)
	/Users/vinairachakonda/go/src/dolthub/dolt/go/cmd/dolt/commands/sql.go:861 +0x76d
github.com/dolthub/dolt/go/cmd/dolt/commands.execShell({0x2b83e70, 0xc00002a6f0}, 0x281b8b2, 0x4, {0xc0001c69dc, 0x4b8})
	/Users/vinairachakonda/go/src/dolthub/dolt/go/cmd/dolt/commands/sql.go:383 +0xd2
github.com/dolthub/dolt/go/cmd/dolt/commands.SqlCmd.Exec({{0x281d757, 0xc0005f1900}}, {0x2b83e70, 0xc00002a6f0}, {0xc0006dc600, 0x8}, {0xc0001ac010, 0x0, 0x0}, 0xc0006f40b0)
	/Users/vinairachakonda/go/src/dolthub/dolt/go/cmd/dolt/commands/sql.go:233 +0x6bc
github.com/dolthub/dolt/go/cmd/dolt/cli.SubCommandHandler.handleCommand({{0x281b836, 0x4}, {0x2834585, 0x11}, {0x0, 0x0}, {0xc0003c02c0, 0x2b, 0x2b}, 0x0}, ...)
	/Users/vinairachakonda/go/src/dolthub/dolt/go/cmd/dolt/cli/command.go:222 +0x282
github.com/dolthub/dolt/go/cmd/dolt/cli.SubCommandHandler.Exec({{0x281b836, 0x4}, {0x2834585, 0x11}, {0x0, 0x0}, {0xc0003c02c0, 0x2b, 0x2b}, 0x0}, ...)
	/Users/vinairachakonda/go/src/dolthub/dolt/go/cmd/dolt/cli/command.go:179 +0x47f
main.runMain()
	/Users/vinairachakonda/go/src/dolthub/dolt/go/cmd/dolt/dolt.go:345 +0x6e5
main.main()
	/Users/vinairachakonda/go/src/dolthub/dolt/go/cmd/dolt/dolt.go:131 +0x19

[VinaiRachakonda]

This is blocking the peewee ORM

[jennifersp]

is fixed in 8516471