[meta] Port patches from D7, where appropriate

While working on the D8 version, there were also several issues fixed with the D7 version, which mostly didn't get ported to D8, or at least not officially. (Some were fixed separately in both, though. Others were fixed only in D8 and should be backported – but it would be very hard to figure those out. If you fixed something in D8 and still remember, it would be great if you could quickly check whether the bug is still there in D7 and create an issue if that's the case.) So, in order to avoid regressions, we need to review all issues (both to the Search API itself and the (now included again) database backend) since work on the D8 branch started and see which need to be ported – i.e., they still apply in the Drupal 8 version and their bug wasn't fixed/their feature not added in D8, yet.

This is a list of all issues committed to the two projects since February 2014 (some older ones might be applicable, too, but it's improbable):

• #2375447: Code out of the loop
• #1861134: Drush sapi-i doesn't work with multiple indexes
• #2347367: Fix forgotten usages of $index->item_type
• #2359201: Combine multiple integer fields in views
• #2364247: SearchApiQueryFilterInterface::getFilters()'s return value is underdocumented
• #2364875: _search_api_views_add_handlers() uses the wrong handler for text types
• #1184610: Limit indexes to specific entity bundles
• #2174163: Nested Taxonomy causes SQL Error on Index
• #2305755: Clear the persistent index field cache when changing aggregated fields
• #2334727: Views caching does not take items_per_page into account
• #1372092: How to setup
• #2305627: Date facets not displayed when the configured granularity is larger than the calculated granularity
• #2110315: Specialized filter for users and terms
• #2319263: Allow server and index classes to be extended
• #2278737: Combine Fulltext Search views filter that contains both all of these words filter and none of these words filter
• #2281535: Adapt to latest changes in Views cache handlers
• #2145547: Exposed sort order doesn't work when combined with non-exposed sort on the same field
• #2146435: Fix Views paging with custom pager add-ons
• #2278791: Excerpt won't be shown when searching single CJK word alone
• #2272983: Fix Highlighting processor for queries without returned results
• #2216345: Notice: Array to string conversion in SearchApiHighlight->postprocessSearchResults()
• #2204847: SearchApiViewsCache does not function correctly with pagination..
• #2265349: Mark _search_api_settings_equals() as deprecated
• #2256891: '0' (zero) label shown as '-0'
• #2233749: Add drush support to change the server used by an index
• #2219553: Fix Views fulltext filter operators
• #2135697: Highlight processor messes up href on hyperlink on search result views page
• #2179755: HTML filter leaves whitespaces
• #2198791: Indexed Content: Author as Exposed Filter: empty field treated as zero (Anonymous)
• #2195469: Exclude certain fields from search excerpt
• #2169455: Undefined index 'data' when search_api_update_7116() gets executed
• #2219563: Simplify debugging by implementing __toString() for queries and filters
• #1888174: Offset between stored and indexed date
• #2187487: Undefined index: options in SearchApiViewsHandlerFilterLanguage->admin_summary
• #2198261: Fatal error on view editing
• #2168713: Warning: preg_match(): Unknown modifier '(' in SearchApiHighlight->createExcerpt()
• #2361329: Fix behavior of "is not" conditions on multi-valued fields
• #2346459: 1.4 update breaks search functionality when using PostgreSQL
• #2318865: Fix error when Mbstring extension is not available
• #2231453: Case sensitivity for Autocomplete
• #2305107: Fix standards-compliance of the generated SQL queries
• #2237829: Add a hook and methods for more specific altering of searches
• #2286329: Incorrect facet counts in multi-word search
• #2265353: Remove uses of _search_api_settings_equals()
• #2147361: Use Database::getConnection() instead of setDb() magic
• #1299238: Add option for partial matching
• #1912332: Facets require "CREATE TEMPORARY TABLES" permission
• #2231829: Postgres: Exception when score is not an integer
• #2219525: Fix tests in PostgreSQL
• #2207205: Change score from float to int
• #2140321: PDOException: SQLSTATE[42803]: Grouping error using Postgres 9.1
• #2170689: Use a (word, field_name) covering index on text tables
• #1144620: Fix character collation problems
• #1390586: Add support for OR facets
• #1658964: Make available: facets with counts of 0
• #2170681: Remove a temporary and a filesort from text queries

If you want to help, please pick one or more to review, remove them from the list here (just striking them through is probably not a good idea, as this wouldn't be distinguishable from closed issues) and then, as appropriate, either keep them closed (although it would probably be a good idea to still add a short comment about why this doesn't need to be ported – for future reference) or move them to project "Search API" (if not already), version "8.x-1.x-dev" and status "Patch (to be ported)".
It would of course be also great if you would then provide some details on what needs to happen, or even provide a new patch for D8 yourself – but reopening is the first step, and important to do primarily, so the issues don't get lost.

If the issue is still open, for whatever reason, use your best judgement on whether to just comment on it (maybe adding a "needs port" tag or something) or move it to D8 nevertheless.
Of course, it's important to really only remove those issues you can review right away (or maybe have already reviewed, to be sure) – otherwise an issue might slip through the cracks after all.