cmd/go/internal/modload: only check root-promotion during tidy for lazy modules

In a lazy module, it is important that tidyRoots does not add any new
roots because the dependencies of non-roots are pruned out.

In an eager module, that property is not important (and does not hold
in general) because no dependencies are ever pruned out.

Fixes #45952

Change-Id: I5c95b5696b7112b9219e38af04e0dece7fb6e202
Reviewed-on: https://go-review.googlesource.com/c/go/+/316754
Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

1 files changed, 11 insertions, 7 deletions

diff --git a/src/cmd/go/internal/modload/load.go b/src/cmd/go/internal/modload/load.go
index f434b399d8..c811029ab5 100644
--- a/src/cmd/go/internal/modload/load.go
+++ b/src/cmd/go/internal/modload/load.go
@@ -1065,13 +1065,17 @@ func loadFromRoots(ctx context.Context, params loaderParams) *loader {
 			ld.errorf("go: %v\n", err)
 		}
 
-		// We continuously add tidy roots to ld.requirements during loading, so at
-		// this point the tidy roots should be a subset of the roots of
-		// ld.requirements. If not, there is a bug in the loading loop above.
-		for _, m := range rs.rootModules {
-			if v, ok := ld.requirements.rootSelected(m.Path); !ok || v != m.Version {
-				ld.errorf("go: internal error: a requirement on %v is needed but was not added during package loading\n", m)
-				base.ExitIfErrors()
+		if ld.requirements.depth == lazy {
+			// We continuously add tidy roots to ld.requirements during loading, so at
+			// this point the tidy roots should be a subset of the roots of
+			// ld.requirements, ensuring that no new dependencies are brought inside
+			// the lazy-loading horizon.
+			// If that is not the case, there is a bug in the loading loop above.
+			for _, m := range rs.rootModules {
+				if v, ok := ld.requirements.rootSelected(m.Path); !ok || v != m.Version {
+					ld.errorf("go: internal error: a requirement on %v is needed but was not added during package loading\n", m)
+					base.ExitIfErrors()
+				}
 			}
 		}
 		ld.requirements = rs