Breaking: make iterator.seek() a mandatory feature

All first-party implementations already support it (`classic-level`,
`memory-level`, `browser-level`, `many-level` and `rave-level`).

Category: change

README.md

@@ -597,8 +597,6 @@ The optional `options` object may contain:
 
 If range options like `gt` were passed to `db.iterator()` and `target` does not fall within that range, the iterator will reach its natural end.
 
-**Note:** Not all implementations support `seek()`. Consult `db.supports.seek` or the [support matrix](https://github.com/Level/supports#seek-boolean).
-
 #### `iterator.close()`
 
 Free up underlying resources. Returns a promise. Closing the iterator is an idempotent operation, such that calling `close()` more than once is allowed and makes no difference.
@@ -1349,14 +1347,14 @@ When a sublevel prefix contains characters outside of the supported byte range.
 
 #### `LEVEL_NOT_SUPPORTED`
 
-When a module needs a certain feature, typically as indicated by `db.supports`, but that feature is not available on a database argument or other. For example, some kind of plugin may depend on `seek()`:
+When a module needs a certain feature, typically as indicated by `db.supports`, but that feature is not available on a database argument or other. For example, some kind of plugin may depend on snapshots:
 
 ```js
 const ModuleError = require('module-error')
 
 module.exports = function plugin (db) {
-  if (!db.supports.seek) {
-    throw new ModuleError('Database must support seeking', {
+  if (!db.supports.explicitSnapshots) {
+    throw new ModuleError('Database must support snapshots', {
       code: 'LEVEL_NOT_SUPPORTED'
     })
   }
@@ -1767,7 +1765,7 @@ The default `_all()` is a functional default that makes repeated calls to `_next
 
 #### `iterator._seek(target, options)`
 
-Seek to the key closest to `target`. The `options` object will always have the following properties: `keyEncoding`. This method is optional. The default will throw an error with code [`LEVEL_NOT_SUPPORTED`](#errors). If supported, set `db.supports.seek` to `true` (via the manifest passed to the database constructor) which also enables relevant tests in the [test suite](#test-suite).
+Seek to the key closest to `target`. The `options` object will always have the following properties: `keyEncoding`. The default `_seek()` will throw an error with code [`LEVEL_NOT_SUPPORTED`](#errors) and must be overridden.
 
 #### `iterator._close()`
 
@@ -1921,7 +1919,7 @@ test('custom test', function (t) {
   // ..
 })
 
-testCommon.supports.seek && test('another test', function (t) {
+testCommon.supports.explicitSnapshots && test('another test', function (t) {
   const db = testCommon.factory()
   // ..
 })

abstract-iterator.js

@@ -226,7 +226,7 @@ class CommonIterator {
   }
 
   _seek (target, options) {
-    throw new ModuleError('Iterator does not support seek()', {
+    throw new ModuleError('Iterator does not implement seek()', {
       code: 'LEVEL_NOT_SUPPORTED'
     })
   }

abstract-level.js

@@ -52,8 +52,7 @@ class AbstractLevel extends EventEmitter {
     this.hooks = new DatabaseHooks()
     this.supports = supports(manifest, {
       deferredOpen: true,
-
-      // TODO (next major): add seek
+      seek: true,
       implicitSnapshots,
       permanence: manifest.permanence !== false,
 

test/index.js

@@ -36,6 +36,7 @@ function suite (options) {
   require('./iterator-test').all(test, testCommon)
   require('./iterator-range-test').all(test, testCommon)
   require('./async-iterator-test').all(test, testCommon)
+  require('./iterator-seek-test').all(test, testCommon)
 
   require('./deferred-open-test').all(test, testCommon)
   require('./encoding-test').all(test, testCommon)
@@ -44,10 +45,6 @@ function suite (options) {
   require('./encoding-buffer-test').all(test, testCommon)
   require('./encoding-decode-error-test').all(test, testCommon)
 
-  if (testCommon.supports.seek) {
-    require('./iterator-seek-test').all(test, testCommon)
-  }
-
   if (testCommon.supports.implicitSnapshots) {
     require('./iterator-snapshot-test').all(test, testCommon)
   } else {

test/self/sublevel-test.js

@@ -251,12 +251,12 @@ test('sublevel manifest and parent db', function (t) {
   t.test('sublevel inherits manifest from parent db', function (t) {
     const parent = new AbstractLevel({
       encodings: { utf8: true },
-      seek: true,
+      explicitSnapshots: true,
       foo: true
     })
     const sub = parent.sublevel('')
     t.is(sub.supports.foo, true, 'AbstractSublevel inherits from parent')
-    t.is(sub.supports.seek, true, 'AbstractSublevel inherits from parent')
+    t.is(sub.supports.explicitSnapshots, true, 'AbstractSublevel inherits from parent')
     t.end()
   })