clean: suggest using `core.longPaths` if paths are too long to remove

On Windows, git repositories may have extra files which need cleaned
(e.g., a build directory) that may be arbitrarily deep. Suggest using
`core.longPaths` if such situations are encountered.

Fixes: #2715
Signed-off-by: Ben Boeckel <mathstuf@gmail.com>

Documentation/config/advice.txt

@@ -118,6 +118,9 @@ advice.*::
 	waitingForEditor::
 		Print a message to the terminal whenever Git is waiting for
 		editor input from the user.
+	nameTooLong::
+		Advice shown if a filepath operation is attempted where the
+		path was too long.
 	nestedTag::
 		Advice shown if a user attempts to recursively tag a tag object.
 	submoduleAlternateErrorStrategyDie::

advice.c

@@ -48,6 +48,7 @@ static struct {
 	[ADVICE_GRAFT_FILE_DEPRECATED]			= { "graftFileDeprecated", 1 },
 	[ADVICE_IGNORED_HOOK]				= { "ignoredHook", 1 },
 	[ADVICE_IMPLICIT_IDENTITY]			= { "implicitIdentity", 1 },
+	[ADVICE_NAME_TOO_LONG]				= { "nameTooLong", 1 },
 	[ADVICE_NESTED_TAG]				= { "nestedTag", 1 },
 	[ADVICE_OBJECT_NAME_WARNING]			= { "objectNameWarning", 1 },
 	[ADVICE_PUSH_ALREADY_EXISTS]			= { "pushAlreadyExists", 1 },

advice.h

@@ -26,6 +26,7 @@ struct string_list;
 	ADVICE_GRAFT_FILE_DEPRECATED,
 	ADVICE_IGNORED_HOOK,
 	ADVICE_IMPLICIT_IDENTITY,
+	ADVICE_NAME_TOO_LONG,
 	ADVICE_NESTED_TAG,
 	ADVICE_OBJECT_NAME_WARNING,
 	ADVICE_PUSH_ALREADY_EXISTS,

builtin/clean.c

@@ -211,6 +211,9 @@ static int remove_dirs(struct strbuf *path, const char *prefix, int force_flag,
 			quote_path(path->buf, prefix, &quoted, 0);
 			errno = saved_errno;
 			warning_errno(_(msg_warn_remove_failed), quoted.buf);
+			if (saved_errno == ENAMETOOLONG) {
+				advise_if_enabled(ADVICE_NAME_TOO_LONG, _("Setting `core.longPaths` may allow the deletion to succeed."));
+			}
 			*dir_gone = 0;
 		}
 		ret = res;
@@ -246,6 +249,9 @@ static int remove_dirs(struct strbuf *path, const char *prefix, int force_flag,
 				quote_path(path->buf, prefix, &quoted, 0);
 				errno = saved_errno;
 				warning_errno(_(msg_warn_remove_failed), quoted.buf);
+				if (saved_errno == ENAMETOOLONG) {
+					advise_if_enabled(ADVICE_NAME_TOO_LONG, _("Setting `core.longPaths` may allow the deletion to succeed."));
+				}
 				*dir_gone = 0;
 				ret = 1;
 			}
@@ -289,6 +295,9 @@ static int remove_dirs(struct strbuf *path, const char *prefix, int force_flag,
 				quote_path(path->buf, prefix, &quoted, 0);
 				errno = saved_errno;
 				warning_errno(_(msg_warn_remove_failed), quoted.buf);
+				if (saved_errno == ENAMETOOLONG) {
+					advise_if_enabled(ADVICE_NAME_TOO_LONG, _("Setting `core.longPaths` may allow the deletion to succeed."));
+				}
 				*dir_gone = 0;
 				ret = 1;
 			}
@@ -1108,6 +1117,9 @@ int cmd_clean(int argc, const char **argv, const char *prefix)
 				qname = quote_path(item->string, NULL, &buf, 0);
 				errno = saved_errno;
 				warning_errno(_(msg_warn_remove_failed), qname);
+				if (saved_errno == ENAMETOOLONG) {
+					advise_if_enabled(ADVICE_NAME_TOO_LONG, _("Setting `core.longPaths` may allow the deletion to succeed."));
+				}
 				errors++;
 			} else if (!quiet) {
 				qname = quote_path(item->string, NULL, &buf, 0);