[performance] cache more database calls, reduce required database calls overall (#3290)

* improvements to caching for lists and relationship to accounts / follows

* fix nil panic in AddToList()

* ensure list related caches are correctly invalidated

* ensure returned ID lists are ordered correctly

* bump go-structr to v0.8.9 (returns early if zero uncached keys to be loaded)

* remove zero checks in uncached key load functions (go-structr now handles this)

* fix issues after rebase on upstream/main

* update the expected return order of CSV exports (since list entries are now down by entry creation date)

* rename some funcs, allow deleting list entries for multiple follow IDs at a time, fix up more tests

* use returning statements on delete to get cache invalidation info

* fixes to recent database delete changes

* fix broken list entries delete sql

* remove unused db function

* update remainder of delete functions to behave in similar way, some other small tweaks

* fix delete user sql, allow returning on err no entries

* uncomment + fix list database tests

* update remaining list tests

* update envparsing test

* add comments to each specific key being invalidated

* add more cache invalidation explanatory comments

* whoops; actually delete poll votes from database in the DeletePollByID() func

* remove added but-commented-out field

* improved comment regarding paging being disabled

* make cache invalidation comments match what's actually happening

* fix up delete query comments to match what is happening

* rename function to read a bit better

* don't use ErrNoEntries on delete when not needed (it's only needed for a RETURNING call)

* update function name in test

* move list exclusivity check to AFTER eligibility check. use log.Panic() instead of panic()

* use the poll_id column in poll_votes for selecting votes in poll ID

* fix function name

1 files changed, 26 insertions, 4 deletions

diff --git a/internal/util/unique.go b/internal/util/unique.go
index bad553d3f..68c1d1235 100644
--- a/internal/util/unique.go
+++ b/internal/util/unique.go
@@ -17,12 +17,23 @@
 
 package util
 
+// KeyBy creates a map of T->S, keyed by value returned from key func.
+func KeyBy[S any, T comparable](in []S, key func(S) T) map[T]S {
+	if key == nil {
+		panic("nil func")
+	}
+	m := make(map[T]S, len(in))
+	for _, v := range in {
+		m[key(v)] = v
+	}
+	return m
+}
+
 // Set represents a hashmap of only keys,
 // useful for deduplication / key checking.
 type Set[T comparable] map[T]struct{}
 
-// ToSet creates a Set[T] from given values,
-// noting that this does not maintain any order.
+// ToSet creates a Set[T] from given values.
 func ToSet[T comparable](in []T) Set[T] {
 	set := make(Set[T], len(in))
 	for _, v := range in {
@@ -31,8 +42,19 @@ func ToSet[T comparable](in []T) Set[T] {
 	return set
 }
 
-// FromSet extracts the values from set to slice,
-// noting that this does not maintain any order.
+// ToSetFunc creates a Set[T] from input slice, keys provided by func.
+func ToSetFunc[S any, T comparable](in []S, key func(S) T) Set[T] {
+	if key == nil {
+		panic("nil func")
+	}
+	set := make(Set[T], len(in))
+	for _, v := range in {
+		set[key(v)] = struct{}{}
+	}
+	return set
+}
+
+// FromSet extracts the values from set to slice.
 func FromSet[T comparable](in Set[T]) []T {
 	out := make([]T, len(in))
 	var i int