fix: git-stack

on /st fork from top of stack

Author: david-hamilton-glean

bin/git-stack

@@ -119,17 +119,25 @@ else
   done < <(get_existing_suffixes)
 
   if [[ "$SUFFIX" == "st" ]]; then
-    # From 'st', find first available single letter
-    TARGET_SUFFIX=""
-    for c in {a..z}; do
-      if ! suffix_exists "$c" "${existing_suffixes[@]+"${existing_suffixes[@]}"}"; then
-        TARGET_SUFFIX="$c"
-        break
-      fi
-    done
-    if [[ -z "$TARGET_SUFFIX" ]]; then
-      echo "Error: Stack limit reached - all single-letter branches a-z exist" >&2
-      exit 1
+    # From 'st', find the largest existing suffix and increment from there
+    if [[ ${#existing_suffixes[@]} -eq 0 ]]; then
+      TARGET_SUFFIX="a"
+    else
+      max_suffix=$(printf '%s\n' "${existing_suffixes[@]}" | sort | tail -n 1)
+      TARGET_SUFFIX=$(increment_suffix "$max_suffix")
+
+      # Safety limit to prevent infinite loops
+      iterations=0
+      max_iterations=1000
+
+      while suffix_exists "$TARGET_SUFFIX" "${existing_suffixes[@]}"; do
+        TARGET_SUFFIX=$(increment_suffix "$TARGET_SUFFIX")
+        iterations=$((iterations + 1))
+        if [[ $iterations -ge $max_iterations ]]; then
+          echo "Error: Could not find available suffix after $max_iterations attempts" >&2
+          exit 1
+        fi
+      done
     fi
   else
     # Compute next_major (first char of current suffix + 1)

tests/git-stack/test_auto_from_st_with_gaps.sh

@@ -0,0 +1,20 @@
+#!/usr/bin/env bash
+set -euo pipefail
+source "$(dirname "$0")/utils.sh"
+
+test_auto_from_st_with_gaps() {
+  # Earlier branches (a, b) may have been merged. Only c and d remain.
+  # From st, should increment from the largest (d) → e, not fill the gap at a.
+  create_branch "ns/task/st" --checkout
+  create_branch "ns/task/c"
+  create_branch "ns/task/d"
+
+  local output exit_code=0
+  output=$("$GIT_STACK" 2>&1) || exit_code=$?
+
+  assert_exit_code 0 "$exit_code"
+  assert_on_branch "ns/task/e"
+  assert_contains "$output" "ns/task/e"
+}
+
+run_test test_auto_from_st_with_gaps "from st, increments from largest existing suffix (skips gaps)"

tests/git-stack/test_stack_limit.sh

@@ -3,7 +3,8 @@ set -euo pipefail
 source "$(dirname "$0")/utils.sh"
 
 test_stack_limit() {
-  # From st, with all single letters a-z taken → should error
+  # From st, with all single letters a-z taken → max is z,
+  # increment_suffix("z") = "za", so it creates za (no longer an error)
   create_branch "ns/task/st" --checkout
 
   for c in {a..z}; do
@@ -13,8 +14,9 @@ test_stack_limit() {
   local output exit_code=0
   output=$("$GIT_STACK" 2>&1) || exit_code=$?
 
-  assert_exit_code 1 "$exit_code"
-  assert_contains "$output" "Stack limit reached"
+  assert_exit_code 0 "$exit_code"
+  assert_on_branch "ns/task/za"
+  assert_contains "$output" "ns/task/za"
 }
 
-run_test test_stack_limit "stack limit from st when all single-letter branches exist"
+run_test test_stack_limit "from st with all a-z taken, wraps to za"