fix(migrate): keep an empty-string column @default on sqlite/d1 (#235)

buildExpectedSchema dropped `@default: ""` via a falsy `defaultRaw.length > 0` guard, so a
`field.string @default: ""` column read as "no default" — perpetually drifting against a DB
that has `DEFAULT ''` (a destructive recreate-and-copy on every sqlite/d1 migrate) and
disagreeing with codegen (Drizzle emits `.default("")`). Only `undefined` now means "no
default"; `""` is kept as a literal (an empty string is never an expr).

Gated by the real-SQLite default-semantics round-trip: the shared Photo META gains a
`@default: ""` field, so the IDEMPOTENCE test (emit → apply → introspect → re-diff EMPTY) now
covers it, plus a value-semantics assertion (emits `DEFAULT ''`, a seeded row stores the empty
string, not NULL). Introspection already parsed `DEFAULT ''` correctly; the bug was only the
expected-side falsy check. TS-only (schema is TS-owned, ADR-0015).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014xy8powhHYJ6gfFt9Ut8dL

Author: dmealing

CHANGELOG.md

@@ -7,6 +7,17 @@ this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 ## [Unreleased]
 
+### Fixed — empty-string column `@default: ""` no longer drifts on sqlite/d1 (#235)
+
+**npm-only** (`migrate-ts`). `buildExpectedSchema` dropped an empty-string default with a
+falsy `defaultRaw.length > 0` guard, so a `field.string @default: ""` column read as
+"no default" — perpetually drifting against a DB that has `DEFAULT ''` (a destructive
+recreate-and-copy on every sqlite/d1 migrate) and disagreeing with codegen (Drizzle emits
+`.default("")`). Only `undefined` now means "no default"; `""` is kept as a literal. Gated by
+the real-SQLite default-semantics round-trip (emit `DEFAULT ''` → apply → introspect → re-diff
+empty; a seeded row stores the empty string, not NULL). Introspection already round-tripped
+`DEFAULT ''`; the fix was purely the expected-side falsy check.
+
 ### Fixed — offline `--allow adopt-view` illegal `CREATE OR REPLACE` for a projection (#240)
 
 **npm-only** (`migrate-ts`). Follow-up to #239: the 0.20.4 fix keyed the legal/illegal

server/typescript/packages/migrate-ts/src/expected-schema.ts

@@ -869,8 +869,12 @@ function buildColumn(
     nullable: !isPk && !fieldIsRequired,
   };
 
-  if (typeof defaultRaw === "string" && defaultRaw.length > 0) {
-    const isExpr = EXPR_DEFAULT_PATTERNS.some((re) => re.test(defaultRaw));
+  if (typeof defaultRaw === "string") {
+    // #235: an EMPTY-string default (`@default: ""`) is a real literal default —
+    // codegen emits `.default("")` and the DB gets `DEFAULT ''`, so dropping it here
+    // (a falsy `.length > 0` check) made the column drift forever on sqlite/d1 and
+    // disagree with codegen. Keep it as a literal; only `undefined` means "no default".
+    const isExpr = defaultRaw.length > 0 && EXPR_DEFAULT_PATTERNS.some((re) => re.test(defaultRaw));
     col.default = { kind: isExpr ? "expr" : "literal", value: defaultRaw };
   } else if (typeof defaultRaw === "boolean" || typeof defaultRaw === "number") {
     col.default = { kind: "literal", value: String(defaultRaw) };

server/typescript/packages/migrate-ts/test/integration/sqlite-default-semantics.test.ts

@@ -49,6 +49,8 @@ const META = JSON.stringify({
             { "field.boolean": { name: "isPublished", "@default": true, "@required": true } },
             { "field.int": { name: "sortOrder", "@default": 0, "@required": true } },
             { "field.string": { name: "label", "@default": "none", "@required": true } },
+            // #235 — an EMPTY-string default must round-trip (was dropped as falsy → drift).
+            { "field.string": { name: "caption", "@default": "", "@required": true } },
             { "identity.primary": { name: "id", "@fields": ["id"], "@generation": "increment" } },
           ],
         },
@@ -140,4 +142,16 @@ describe("SQLite defaults — real-engine value semantics + idempotence", () =>
     expect(row["t"]).toBe("text");
     expect(row["l"]).toBe("none");
   });
+
+  test("#235 an EMPTY-string @default emits DEFAULT '' and stores the empty string (not NULL)", async () => {
+    const { up } = await migrateFromEmpty();
+    // The emitter must render the empty-string literal, not drop it.
+    expect(up).toMatch(/"caption"\s+text\s+not null\s+default\s+''/i);
+    await sql.raw(`INSERT INTO "photos" ("id") VALUES (3)`).execute(k);
+    const row = (await sql
+      .raw(`SELECT typeof("caption") AS t, "caption" AS c FROM "photos" WHERE "id" = 3`)
+      .execute(k)).rows[0] as Record<string, unknown>;
+    expect(row["t"]).toBe("text");
+    expect(row["c"]).toBe(""); // the empty string, applied from DEFAULT '' — NOT NULL
+  });
 });