internal/lsp/cache: use GetHandle not Bind for 5 URI-keyed maps

This change replaces the 5 remaining calls to Bind (generational
lifetime) with GetHandle (reference counting). The handles
are now stored in persistent.Maps, which simplifies the
invalidation logic.

All 5 have span.URIs as keys:
  symbolizeHandles
  parse{Mod,Work}Handles
  mod{Tidy,Why}Handles

Also, factor the functions that use these maps to have a common form:
- a fooImpl function that returns an R result and an error;
- a foo wrapper that decorates it with caching.
- a local fooResult type, defined struct{R; error} that is the cache entry.
The functions for getting/setting map entries are all inlined.
The fooHandle types are all replaced by *memoize.Handle, now that
their use is local.

No behavior change is intended.

The other uses of Bind are deleted in these CLs:
https://go-review.googlesource.com/c/tools/+/415975 (astCacheData)
https://go-review.googlesource.com/c/tools/+/415504 (actions)

Change-Id: I77cc4e828936fe171152ca13a12f7a639299e9e5
Reviewed-on: https://go-review.googlesource.com/c/tools/+/415976
Auto-Submit: Alan Donovan <adonovan@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Alan Donovan <adonovan@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>

1 files changed, 7 insertions, 6 deletions

diff --git a/internal/lsp/cache/maps.go b/internal/lsp/cache/maps.go
index f8e03057c..1ec341515 100644
--- a/internal/lsp/cache/maps.go
+++ b/internal/lsp/cache/maps.go
@@ -16,11 +16,14 @@ type filesMap struct {
 	impl *persistent.Map
 }
 
+// uriLessInterface is the < relation for "any" values containing span.URIs.
+func uriLessInterface(a, b interface{}) bool {
+	return a.(span.URI) < b.(span.URI)
+}
+
 func newFilesMap() filesMap {
 	return filesMap{
-		impl: persistent.NewMap(func(a, b interface{}) bool {
-			return a.(span.URI) < b.(span.URI)
-		}),
+		impl: persistent.NewMap(uriLessInterface),
 	}
 }
 
@@ -152,9 +155,7 @@ type parseKeysByURIMap struct {
 
 func newParseKeysByURIMap() parseKeysByURIMap {
 	return parseKeysByURIMap{
-		impl: persistent.NewMap(func(a, b interface{}) bool {
-			return a.(span.URI) < b.(span.URI)
-		}),
+		impl: persistent.NewMap(uriLessInterface),
 	}
 }