[PATCH v4 1/5] advice: add stashBeforeCheckout advice for dirty branch switches

["Arsh Srivastava via GitGitGadget" <gitgitgadget@gmail.com>]

From: Arsh Srivastava <arshsrivastava00@gmail.com>

Add a new advice type ADVICE_STASH_BEFORE_CHECKOUT to guide users
when they attempt to switch branches with local modifications that
would be overwritten by the operation.

This includes:
> New ADVICE_STASH_BEFORE_CHECKOUT enum value in advice.h
> Corresponding "stashBeforeCheckout" entry in advice_setting[]
> New advise_on_checkout_dirty_files() function that lists the
  affected files and suggests using git stash push/pop
> Documentation entry in Documentation/config/advice.txt

The advice follows existing patterns established by
advise_on_updating_sparse_paths() and can be silenced with:

  git config set advice.stashBeforeCheckout false

Signed-off-by: Arsh Srivastava <arshsrivastava00@gmail.com>
---
 Documentation/config/advice.adoc |  5 +++++
 advice.c                         | 27 +++++++++++++++++++++++++++
 advice.h                         |  2 ++
 3 files changed, 34 insertions(+)

diff --git a/Documentation/config/advice.adoc b/Documentation/config/advice.adoc
index 257db58918..8752e05636 100644
--- a/Documentation/config/advice.adoc
+++ b/Documentation/config/advice.adoc
@@ -126,6 +126,11 @@ all advice messages.
 		Shown when a sparse index is expanded to a full index, which is likely
 		due to an unexpected set of files existing outside of the
 		sparse-checkout.
+	stashBeforeCheckout::
+		Shown when the user attempts to switch branches but has
+		local modifications that would be overwritten by the
+		operation, to suggest using linkgit:git-stash[1] to
+		save changes before switching.
 	statusAheadBehind::
 		Shown when linkgit:git-status[1] computes the ahead/behind
 		counts for a local ref compared to its remote tracking ref,
diff --git a/advice.c b/advice.c
index 0018501b7b..e1264f525c 100644
--- a/advice.c
+++ b/advice.c
@@ -81,6 +81,7 @@ static struct {
 	[ADVICE_SET_UPSTREAM_FAILURE]			= { "setUpstreamFailure" },
 	[ADVICE_SKIPPED_CHERRY_PICKS]			= { "skippedCherryPicks" },
 	[ADVICE_SPARSE_INDEX_EXPANDED]			= { "sparseIndexExpanded" },
+	[ADVICE_STASH_BEFORE_CHECKOUT] = { "stashBeforeCheckout" },
 	[ADVICE_STATUS_AHEAD_BEHIND_WARNING]		= { "statusAheadBehindWarning" },
 	[ADVICE_STATUS_HINTS]				= { "statusHints" },
 	[ADVICE_STATUS_U_OPTION]			= { "statusUoption" },
@@ -312,3 +313,29 @@ void advise_on_moving_dirty_path(struct string_list *pathspec_list)
 			    "* Use \"git add --sparse <paths>\" to update the index\n"
 			    "* Use \"git sparse-checkout reapply\" to apply the sparsity rules"));
 }
+
+void advise_on_checkout_dirty_files(struct string_list *file_list)
+{
+    struct string_list_item *item;
+
+    if (!file_list->nr)
+	return;
+
+    fprintf(stderr, _("The following files have local modifications that would\n"
+		      "be overwritten by switching branches:\n"));
+    for_each_string_list_item(item, file_list)
+	fprintf(stderr, "\t%s\n", item->string);
+
+    advise_if_enabled(ADVICE_STASH_BEFORE_CHECKOUT,
+		      _("You can save your local changes before switching by running:\n"
+			"\n"
+			"\tgit stash push\n"
+			"\n"
+			"Then restore them after switching with:\n"
+			"\n"
+			"\tgit stash pop\n"
+			"\n"
+			"Or to discard your local changes, use:\n"
+			"\n"
+			"\tgit checkout -- <file>"));
+}
diff --git a/advice.h b/advice.h
index 8def280688..c035b5d8e3 100644
--- a/advice.h
+++ b/advice.h
@@ -48,6 +48,7 @@ enum advice_type {
 	ADVICE_SET_UPSTREAM_FAILURE,
 	ADVICE_SKIPPED_CHERRY_PICKS,
 	ADVICE_SPARSE_INDEX_EXPANDED,
+	ADVICE_STASH_BEFORE_CHECKOUT,
 	ADVICE_STATUS_AHEAD_BEHIND_WARNING,
 	ADVICE_STATUS_HINTS,
 	ADVICE_STATUS_U_OPTION,
@@ -83,5 +84,6 @@ void NORETURN die_ff_impossible(void);
 void advise_on_updating_sparse_paths(struct string_list *pathspec_list);
 void detach_advice(const char *new_name);
 void advise_on_moving_dirty_path(struct string_list *pathspec_list);
+void advise_on_checkout_dirty_files(struct string_list *file_list);
 
 #endif /* ADVICE_H */
-- 
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