advice: update message to suggest '--sparse'

The previous changes modified the behavior of 'git add', 'git rm', and
'git mv' to not adjust paths outside the sparse-checkout cone, even if
they exist in the working tree and their cache entries lack the
SKIP_WORKTREE bit. The intention is to warn users that they are doing
something potentially dangerous. The '--sparse' option was added to each
command to allow careful users the same ability they had before.

To improve the discoverability of this new functionality, add a message
to advice.updateSparsePath that mentions the existence of the option.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>

advice.c

@@ -300,7 +300,8 @@ void advise_on_updating_sparse_paths(struct string_list *pathspec_list)
 		fprintf(stderr, "%s\n", item->string);
 
 	advise_if_enabled(ADVICE_UPDATE_SPARSE_PATH,
-			  _("Disable or modify the sparsity rules if you intend"
+			  _("Disable or modify the sparsity rules or"
+			    " use the --sparse option if you intend"
 			    " to update such entries."));
 }
 

t/t3602-rm-sparse-checkout.sh

@@ -16,7 +16,7 @@ test_expect_success 'setup' "
 	EOF
 
 	cat >sparse_hint <<-EOF &&
-	hint: Disable or modify the sparsity rules if you intend to update such entries.
+	hint: Disable or modify the sparsity rules or use the --sparse option if you intend to update such entries.
 	hint: Disable this message with \"git config advice.updateSparsePath false\"
 	EOF
 

t/t3705-add-sparse-checkout.sh

@@ -43,7 +43,7 @@ test_expect_success 'setup' "
 	EOF
 
 	cat >sparse_hint <<-EOF &&
-	hint: Disable or modify the sparsity rules if you intend to update such entries.
+	hint: Disable or modify the sparsity rules or use the --sparse option if you intend to update such entries.
 	hint: Disable this message with \"git config advice.updateSparsePath false\"
 	EOF
 

t/t7002-mv-sparse-checkout.sh

@@ -16,7 +16,7 @@ test_expect_success 'setup' "
 	EOF
 
 	cat >sparse_hint <<-EOF
-	hint: Disable or modify the sparsity rules if you intend to update such entries.
+	hint: Disable or modify the sparsity rules or use the --sparse option if you intend to update such entries.
 	hint: Disable this message with \"git config advice.updateSparsePath false\"
 	EOF
 "