more helpful error msgs

Author: skarim

cmd/merge.go

@@ -237,10 +237,12 @@ func resolveActiveRemoteStack(cfg *config.Config, client github.ClientOps) (*git
 	stacks := sf.FindAllStacksForBranch(currentBranch)
 	if len(stacks) == 0 {
 		cfg.Errorf("current branch %q is not part of a stack", currentBranch)
+		cfg.Printf("Checkout a stack first, or specify which stack or pull request to merge with `%s`", cfg.ColorCyan("gh stack merge [number]"))
 		return nil, ErrNotInStack
 	}
 	if len(stacks) > 1 {
-		cfg.Errorf("branch %q belongs to multiple stacks; check out a non-trunk branch first", currentBranch)
+		cfg.Errorf("branch %q belongs to multiple stacks", currentBranch)
+		cfg.Printf("Checkout a stack first, or specify which stack or pull request to merge with `%s`", cfg.ColorCyan("gh stack merge [number]"))
 		return nil, ErrDisambiguate
 	}
 	s := stacks[0]

cmd/merge_test.go

@@ -413,6 +413,8 @@ func TestRunMerge_NoArg_NotInStack(t *testing.T) {
 
 	assert.ErrorIs(t, err, ErrNotInStack)
 	assert.Contains(t, output, "not part of a stack")
+	assert.Contains(t, output, "Checkout a stack first, or specify which stack or pull request to merge with")
+	assert.Contains(t, output, "gh stack merge [number]")
 }
 
 func TestRunMerge_DefaultMethodFallsBackToAllowed(t *testing.T) {