cmd/go/internal/modload: avoid loading the full module graph when listing specific modules

For #36460
For #41297
Updates #29666

Change-Id: I5f324c0ef9a164f8043d2188101d141bb5fa7454
Reviewed-on: https://go-review.googlesource.com/c/go/+/309191
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>
Reviewed-by: Michael Matloob <matloob@golang.org>

1 files changed, 49 insertions, 18 deletions

diff --git a/src/cmd/go/internal/modload/list.go b/src/cmd/go/internal/modload/list.go
index 66927a8288..344b2aa2c7 100644
--- a/src/cmd/go/internal/modload/list.go
+++ b/src/cmd/go/internal/modload/list.go
@@ -82,19 +82,7 @@ func listModules(ctx context.Context, rs *Requirements, args []string, mode List
 		return rs, []*modinfo.ModulePublic{moduleInfo(ctx, rs, Target, mode)}, nil
 	}
 
-	var mg *ModuleGraph
-	if go117LazyTODO {
-		// Pull the args-loop below into another (new) loop.
-		// If the main module is lazy, try it once with mg == nil, and then load mg
-		// and try again.
-	} else {
-		// TODO(#41297): Don't bother loading or expanding the graph if all
-		// arguments are explicit version queries (including if no arguments are
-		// present at all).
-		rs, mg, mgErr = expandGraph(ctx, rs)
-	}
-
-	matchedModule := map[module.Version]bool{}
+	needFullGraph := false
 	for _, arg := range args {
 		if strings.Contains(arg, `\`) {
 			base.Fatalf("go: module paths never use backslash")
@@ -102,19 +90,51 @@ func listModules(ctx context.Context, rs *Requirements, args []string, mode List
 		if search.IsRelativePath(arg) {
 			base.Fatalf("go: cannot use relative path %s to specify module", arg)
 		}
-		if !HasModRoot() {
-			if arg == "all" || strings.Contains(arg, "...") {
+		if arg == "all" || strings.Contains(arg, "...") {
+			needFullGraph = true
+			if !HasModRoot() {
 				base.Fatalf("go: cannot match %q: %v", arg, ErrNoModRoot)
 			}
-			if mode&ListVersions == 0 && !strings.Contains(arg, "@") {
+			continue
+		}
+		if i := strings.Index(arg, "@"); i >= 0 {
+			path := arg[:i]
+			vers := arg[i+1:]
+			if vers == "upgrade" || vers == "patch" {
+				if _, ok := rs.rootSelected(path); !ok || rs.depth == eager {
+					needFullGraph = true
+					if !HasModRoot() {
+						base.Fatalf("go: cannot match %q: %v", arg, ErrNoModRoot)
+					}
+				}
+			}
+			continue
+		}
+		if _, ok := rs.rootSelected(arg); !ok || rs.depth == eager {
+			needFullGraph = true
+			if mode&ListVersions == 0 && !HasModRoot() {
 				base.Fatalf("go: cannot match %q without -versions or an explicit version: %v", arg, ErrNoModRoot)
 			}
 		}
+	}
+
+	var mg *ModuleGraph
+	if needFullGraph {
+		rs, mg, mgErr = expandGraph(ctx, rs)
+	}
+
+	matchedModule := map[module.Version]bool{}
+	for _, arg := range args {
 		if i := strings.Index(arg, "@"); i >= 0 {
 			path := arg[:i]
 			vers := arg[i+1:]
 
-			current := mg.Selected(path)
+			var current string
+			if mg == nil {
+				current, _ = rs.rootSelected(path)
+			} else {
+				current = mg.Selected(path)
+			}
 			if current == "none" && mgErr != nil {
 				if vers == "upgrade" || vers == "patch" {
 					// The module graph is incomplete, so we don't know what version we're
@@ -156,7 +176,18 @@ func listModules(ctx context.Context, rs *Requirements, args []string, mode List
 		} else if strings.Contains(arg, "...") {
 			match = search.MatchPattern(arg)
 		} else {
-			v := mg.Selected(arg)
+			var v string
+			if mg == nil {
+				var ok bool
+				v, ok = rs.rootSelected(arg)
+				if !ok {
+					// We checked rootSelected(arg) in the earlier args loop, so if there
+					// is no such root we should have loaded a non-nil mg.
+					panic(fmt.Sprintf("internal error: root requirement expected but not found for %v", arg))
+				}
+			} else {
+				v = mg.Selected(arg)
+			}
 			if v == "none" && mgErr != nil {
 				// mgErr is already set, so just skip this module.
 				continue