gopls/internal/lsp/cache: fix boundary cond in parseCache age eviction

Setting maxAge=0 should degenerate the parse cache to evict immediately
(necessary to avoid flakiness in tests on platforms with coarse clock
granularity).

Fixes golang/go#61550

Change-Id: I6cb03cfb670faa6c6995fd3c4c5a98dd1dadb344
Reviewed-on: https://go-review.googlesource.com/c/tools/+/512635
Reviewed-by: Bryan Mills <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Robert Findley <[email protected]>
gopls-CI: kokoro <[email protected]>

Author: findleyr

gopls/internal/lsp/cache/parse_cache.go

@@ -95,8 +95,8 @@ var parsePadding = 1000 // mutable for testing
 // caching) multiple files. This is necessary for type-checking, where files
 // must be parsed in a common fileset.
 type parseCache struct {
-	maxAge time.Duration // interval at which to collect expired cache entries
-	done   chan struct{} // closed when GC is stopped
+	expireAfter time.Duration // interval at which to collect expired cache entries
+	done        chan struct{} // closed when GC is stopped
 
 	mu       sync.Mutex
 	m        map[parseKey]*parseCacheEntry
@@ -106,14 +106,14 @@ type parseCache struct {
 }
 
 // newParseCache creates a new parse cache and starts a goroutine to garbage
-// collect old entries that are older than maxAge.
+// collect entries whose age is at least expireAfter.
 //
 // Callers must call parseCache.stop when the parse cache is no longer in use.
-func newParseCache(maxAge time.Duration) *parseCache {
+func newParseCache(expireAfter time.Duration) *parseCache {
 	c := &parseCache{
-		maxAge: maxAge,
-		m:      make(map[parseKey]*parseCacheEntry),
-		done:   make(chan struct{}),
+		expireAfter: expireAfter,
+		m:           make(map[parseKey]*parseCacheEntry),
+		done:        make(chan struct{}),
 	}
 	go c.gc()
 	return c
@@ -275,7 +275,7 @@ func (c *parseCache) gcOnce() {
 
 	for len(c.m) > parseCacheMinFiles {
 		e := heap.Pop(&c.lru).(*parseCacheEntry)
-		if now.Sub(e.walltime) > c.maxAge {
+		if now.Sub(e.walltime) >= c.expireAfter {
 			delete(c.m, e.key)
 		} else {
 			heap.Push(&c.lru, e)

gopls/internal/lsp/cache/parse_cache_test.go

@@ -51,6 +51,9 @@ func TestParseCache(t *testing.T) {
 	files = append(files, dummyFileHandles(parseCacheMinFiles-1)...)
 
 	pgfs3, err := cache.parseFiles(ctx, fset, source.ParseFull, false, files...)
+	if err != nil {
+		t.Fatal(err)
+	}
 	pgf3 := pgfs3[0]
 	if pgf3 != pgf1 {
 		t.Errorf("parseFiles(%q, ...): unexpected cache miss", uri)