fix(init): bound the LocalHostName cache and don't cache lookup failures

Keying the cache on $HOST alone can't notice a LocalHostName rename
while HostName stays fixed, which would pin a stale identity forever.
Expire the entry after a day, like lib/grep.zsh does, so a rename is
picked up without giving up the fork on almost every start.

Only write the cache when scutil actually answered, so a transient
failure falls back to ${HOST/.*/} for that shell instead of pinning the
fallback name for the next day.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

lib/vcs_info.zsh

@@ -38,47 +38,16 @@
 # due to malicious input as a consequence of CVE-2021-45444, which affects
 # zsh versions from 5.0.3 to 5.8.
 #
-# The patch is applied when VCS_INFO_formats is first called, since loading
-# and patching it on every startup costs time in shells that never use
-# vcs_info. `autoload` doesn't replace an already defined function, so this
-# wrapper survives a later `autoload -Uz vcs_info` in a theme or .zshrc, and
-# vcs_info's own `autoload -Uz VCS_INFO_formats`.
-if (( $+functions[VCS_INFO_formats] )); then
-  () {
-    autoload -Uz +X regexp-replace 2>/dev/null || return 1
+autoload -Uz +X regexp-replace VCS_INFO_formats 2>/dev/null || return 0
 
-    # We use $tmp here because it's already a local variable in VCS_INFO_formats
-    local PATCH='for tmp (base base-name branch misc revision subdir) hook_com[$tmp]="${hook_com[$tmp]//\%/%%}"'
-    # Unique string to avoid reapplying the patch if this code gets called twice
-    local PATCH_ID=vcs_info-patch-9b9840f2-91e5-4471-af84-9e9a0dc68c1b
-    # Only patch the VCS_INFO_formats function if not already patched
-    if [[ "$functions[VCS_INFO_formats]" != *$PATCH_ID* ]]; then
-      regexp-replace 'functions[VCS_INFO_formats]' \
-        "VCS_INFO_hook 'post-backend'" \
-        ': ${PATCH_ID}; ${PATCH}; ${MATCH}'
-    fi
-  }
-else
-  function VCS_INFO_formats {
-    local loaded_function="$(
-      unfunction VCS_INFO_formats 2>/dev/null
-      autoload -Uz +X VCS_INFO_formats 2>/dev/null || return 1
-      print -r -- "$functions[VCS_INFO_formats]"
-    )" || return 1
-    functions[VCS_INFO_formats]="$loaded_function"
-    autoload -Uz +X regexp-replace 2>/dev/null || return 1
-
-    # We use $tmp here because it's already a local variable in VCS_INFO_formats
-    local PATCH='for tmp (base base-name branch misc revision subdir) hook_com[$tmp]="${hook_com[$tmp]//\%/%%}"'
-    # Unique string to avoid reapplying the patch if this code gets called twice
-    local PATCH_ID=vcs_info-patch-9b9840f2-91e5-4471-af84-9e9a0dc68c1b
-    # Only patch the VCS_INFO_formats function if not already patched
-    if [[ "$functions[VCS_INFO_formats]" != *$PATCH_ID* ]]; then
-      regexp-replace 'functions[VCS_INFO_formats]' \
-        "VCS_INFO_hook 'post-backend'" \
-        ': ${PATCH_ID}; ${PATCH}; ${MATCH}'
-    fi
-
-    VCS_INFO_formats "$@"
-  }
+# We use $tmp here because it's already a local variable in VCS_INFO_formats
+typeset PATCH='for tmp (base base-name branch misc revision subdir) hook_com[$tmp]="${hook_com[$tmp]//\%/%%}"'
+# Unique string to avoid reapplying the patch if this code gets called twice
+typeset PATCH_ID=vcs_info-patch-9b9840f2-91e5-4471-af84-9e9a0dc68c1b
+# Only patch the VCS_INFO_formats function if not already patched
+if [[ "$functions[VCS_INFO_formats]" != *$PATCH_ID* ]]; then
+  regexp-replace 'functions[VCS_INFO_formats]' \
+    "VCS_INFO_hook 'post-backend'" \
+    ': ${PATCH_ID}; ${PATCH}; ${MATCH}'
 fi
+unset PATCH PATCH_ID

oh-my-zsh.sh

@@ -100,7 +100,23 @@ done
 # Figure out the SHORT hostname
 if [[ "$OSTYPE" = darwin* ]]; then
   # macOS's $HOST changes with dhcp, etc. Use LocalHostName if possible.
-  SHORT_HOST=$(scutil --get LocalHostName 2>/dev/null) || SHORT_HOST="${HOST/.*/}"
+  # scutil costs a fork on every start, so remember its answer for a day
+  # (like lib/grep.zsh) and re-check sooner if $HOST changes.
+  __omz_host_cache="$ZSH_CACHE_DIR/localhostname"
+  __omz_host_cached=("$__omz_host_cache"(Nm-1))
+  if [[ -n "$__omz_host_cached" ]]; then
+    { read -r __omz_host_key && read -r SHORT_HOST } < "$__omz_host_cache"
+  fi
+  if [[ "$__omz_host_key" != "$HOST" || -z "$SHORT_HOST" ]]; then
+    # only cache what scutil actually answered, so a transient failure
+    # doesn't pin the fallback name for a day
+    if SHORT_HOST=$(scutil --get LocalHostName 2>/dev/null) && [[ -n "$SHORT_HOST" ]]; then
+      [[ ! -w "$ZSH_CACHE_DIR" ]] || print -rl -- "$HOST" "$SHORT_HOST" >| "$__omz_host_cache"
+    else
+      SHORT_HOST="${HOST/.*/}"
+    fi
+  fi
+  unset __omz_host_cache __omz_host_cached __omz_host_key
 else
   SHORT_HOST="${HOST/.*/}"
 fi