gopls/internal/lsp/filecache: evict aggressively on Go builders

This change reduces the cache space budget (1GB -> 250MB) and
maximum age (5 days -> 1 hour) when the program appears to be
running on a Go builder, as indicated by GO_BUILDER_NAME.
Previously, the tests were occasionally filling the builders'
temp volumes.

Fixes golang/go#57900

Change-Id: I7cd74c8ca9933db1d8a7eb127b7e1fb76f4b387f
Reviewed-on: https://go-review.googlesource.com/c/tools/+/482823
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Alan Donovan <[email protected]>
Reviewed-by: Robert Findley <[email protected]>
gopls-CI: kokoro <[email protected]>

Author: adonovan

gopls/internal/lsp/filecache/filecache.go

@@ -278,7 +278,17 @@ func gc(goplsDir string) {
 	//    sleeping after every stat (due to OS optimizations).
 	const statDelay = 100 * time.Microsecond // average delay between stats, to smooth out I/O
 	const batchSize = 1000                   // # of stats to process before sleeping
-	const maxAge = 5 * 24 * time.Hour        // max time since last access before file is deleted
+	maxAge := 5 * 24 * time.Hour             // max time since last access before file is deleted
+
+	// This environment variable is set when running under a Go test builder.
+	// We use it to trigger much more aggressive cache eviction to prevent
+	// filling of the tmp volume by short-lived test processes.
+	// A single run of the gopls tests takes on the order of a minute
+	// and produces <50MB of cache data, so these are still generous.
+	if os.Getenv("GO_BUILDER_NAME") != "" {
+		maxAge = 1 * time.Hour
+		SetBudget(250 * 1e6) // 250MB
+	}
 
 	// The macOS filesystem is strikingly slow, at least on some machines.
 	// /usr/bin/find achieves only about 25,000 stats per second