internal/lsp: use memoize store's context when type checking

The memoize store passes a detached context to the value getter
function. This is important since if the value getter experiences a
context cancellation it will end up caching context.Canceled, which
you never want. When type checking, we were ignoring the detached
context and using the "real" request context. This would cause the
context.Canceled error to get cached and continue popping up in
various situations.

Fix by swapping the importer's context to the detached context. It is
a little messy since the importer stores the context as a field. I
added a defer to restore the original context since it doesn't seem
correct to let the detached context escape the memoize function.

Updates #33678

Change-Id: I20dd466b0072ac2e856adbe993364f77e93ab054
Reviewed-on: https://go-review.googlesource.com/c/tools/+/192719
Reviewed-by: Rebecca Stambler <[email protected]>
Run-TryBot: Rebecca Stambler <[email protected]>

Author: muirdm

internal/lsp/cache/check.go

@@ -94,10 +94,15 @@ func (imp *importer) checkPackageHandle(m *metadata) (*checkPackageHandle, error
 		imports: make(map[packagePath]*checkPackageHandle),
 	}
 	h := imp.view.session.cache.store.Bind(key, func(ctx context.Context) interface{} {
+		origCtx := imp.ctx
+		defer func() { imp.ctx = origCtx }()
+
+		// We must use the store's detached context to avoid poisoning the
+		// cache with context.Canceled if the request is cancelled.
+		imp.ctx = ctx
+
 		data := &checkPackageData{}
-		data.pkg, data.err = func() (*pkg, error) {
-			return imp.typeCheck(cph, m)
-		}()
+		data.pkg, data.err = imp.typeCheck(cph, m)
 		return data
 	})
 	cph.handle = h