cmd/go/internal/modload: implement the "all" pattern for lazy loading

The new semantics of the "all" package pattern can be implemented
without actually changing module loading per se. This change
implements those semantics, so that the change can be decoupled from
the changes to the module requirement graph.

For #36460

Change-Id: I0ee8b17afa8b728dc470a42a540fcc01764a4442
Reviewed-on: https://go-review.googlesource.com/c/go/+/240623
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>
Reviewed-by: Michael Matloob <matloob@golang.org>

1 files changed, 22 insertions, 0 deletions

diff --git a/src/cmd/go/internal/modload/modfile.go b/src/cmd/go/internal/modload/modfile.go
index a45c4a63be..18dd293ac9 100644
--- a/src/cmd/go/internal/modload/modfile.go
+++ b/src/cmd/go/internal/modload/modfile.go
@@ -25,6 +25,11 @@ import (
 	"golang.org/x/mod/semver"
 )
 
+// lazyLoadingVersion is the Go version (plus leading "v") at which lazy module
+// loading takes effect.
+const lazyLoadingVersionV = "v1.16"
+const go116EnableLazyLoading = true
+
 var modFile *modfile.File
 
 // A modFileIndex is an index of data corresponding to a modFile
@@ -249,6 +254,23 @@ func indexModFile(data []byte, modFile *modfile.File, needsFix bool) *modFileInd
 	return i
 }
 
+// allPatternClosesOverTests reports whether the "all" pattern includes
+// dependencies of tests outside the main module (as in Go 1.11–1.15).
+// (Otherwise — as in Go 1.16+ — the "all" pattern includes only the packages
+// transitively *imported by* the packages and tests in the main module.)
+func (i *modFileIndex) allPatternClosesOverTests() bool {
+	if !go116EnableLazyLoading {
+		return true
+	}
+	if i != nil && semver.Compare(i.goVersionV, lazyLoadingVersionV) < 0 {
+		// The module explicitly predates the change in "all" for lazy loading, so
+		// continue to use the older interpretation. (If i == nil, we not in any
+		// module at all and should use the latest semantics.)
+		return true
+	}
+	return false
+}
+
 // modFileIsDirty reports whether the go.mod file differs meaningfully
 // from what was indexed.
 // If modFile has been changed (even cosmetically) since it was first read,