Merge branch 'jh/verify-index-checksum-only-in-fsck'

The index file has a trailing SHA-1 checksum to detect file
corruption, and historically we checked it every time the index
file is used.  Omit the validation during normal use, and instead
verify only in "git fsck".

* jh/verify-index-checksum-only-in-fsck:
read-cache: force_verify_index_checksum

diff --combined cache.h
index 75cce814bd656b3305666ef08fd1dc709babb537,ed3c5927cc5a3fdb6897903433327bde88656ae8..ef0fe43a9df9437bac8e1f78cc1a908798b290fc
--- 1/cache.h
--- 2/cache.h
+++ b/cache.h
@@@ -66,12 -66,8 +66,12 @@@ unsigned long git_deflate_bound(git_zst
  #define GIT_SHA1_RAWSZ 20
  #define GIT_SHA1_HEXSZ (2 * GIT_SHA1_RAWSZ)
  
 +/* The length in byte and in hex digits of the largest possible hash value. */
 +#define GIT_MAX_RAWSZ GIT_SHA1_RAWSZ
 +#define GIT_MAX_HEXSZ GIT_SHA1_HEXSZ
 +
  struct object_id {
 -      unsigned char hash[GIT_SHA1_RAWSZ];
 +      unsigned char hash[GIT_MAX_RAWSZ];
  };
  
  #if defined(DT_UNKNOWN) && !defined(NO_D_TYPE_IN_DIRENT)
@@@ -415,7 -411,6 +415,7 @@@ static inline enum object_type object_t
  #define GIT_WORK_TREE_ENVIRONMENT "GIT_WORK_TREE"
  #define GIT_PREFIX_ENVIRONMENT "GIT_PREFIX"
  #define GIT_SUPER_PREFIX_ENVIRONMENT "GIT_INTERNAL_SUPER_PREFIX"
 +#define GIT_TOPLEVEL_PREFIX_ENVIRONMENT "GIT_INTERNAL_TOPLEVEL_PREFIX"
  #define DEFAULT_GIT_DIR_ENVIRONMENT ".git"
  #define DB_ENVIRONMENT "GIT_OBJECT_DIRECTORY"
  #define INDEX_ENVIRONMENT "GIT_INDEX_FILE"
@@@ -710,6 -705,8 +710,8 @@@ extern void update_index_if_able(struc
  extern int hold_locked_index(struct lock_file *, int);
  extern void set_alternate_index_output(const char *);
  
+ extern int verify_index_checksum;
+ 
  /* Environment bits from configuration mechanism */
  extern int trust_executable_bit;
  extern int trust_ctime;
@@@ -982,7 -979,7 +984,7 @@@ extern char *sha1_pack_index_name(cons
  extern const char *find_unique_abbrev(const unsigned char *sha1, int len);
  extern int find_unique_abbrev_r(char *hex, const unsigned char *sha1, int len);
  
 -extern const unsigned char null_sha1[GIT_SHA1_RAWSZ];
 +extern const unsigned char null_sha1[GIT_MAX_RAWSZ];
  extern const struct object_id null_oid;
  
  static inline int hashcmp(const unsigned char *sha1, const unsigned char *sha2)
@@@ -1164,7 -1161,7 +1166,7 @@@ typedef int create_file_fn(const char *
  int raceproof_create_file(const char *path, create_file_fn fn, void *cb);
  
  int mkdir_in_gitdir(const char *path);
 -extern char *expand_user_path(const char *path);
 +extern char *expand_user_path(const char *path, int real_home);
  const char *enter_repo(const char *path, int strict);
  static inline int is_absolute_path(const char *path)
  {
@@@ -1364,7 -1361,7 +1366,7 @@@ extern int get_sha1_with_context(const 
  
  extern int get_oid(const char *str, struct object_id *oid);
  
 -typedef int each_abbrev_fn(const unsigned char *sha1, void *);
 +typedef int each_abbrev_fn(const struct object_id *oid, void *);
  extern int for_each_abbrev(const char *prefix, each_abbrev_fn, void *);
  
  extern int set_disambiguate_hint_config(const char *var, const char *value);
@@@ -1679,12 -1676,9 +1681,12 @@@ extern struct packed_git *find_sha1_pac
  extern void pack_report(void);
  
  /*
 - * Create a temporary file rooted in the object database directory.
 + * Create a temporary file rooted in the object database directory, or
 + * die on failure. The filename is taken from "pattern", which should have the
 + * usual "XXXXXX" trailer, and the resulting filename is written into the
 + * "template" buffer. Returns the open descriptor.
   */
 -extern int odb_mkstemp(char *template, size_t limit, const char *pattern);
 +extern int odb_mkstemp(struct strbuf *template, const char *pattern);
  
  /*
   * Generate the filename to be used for a pack file with checksum "sha1" and
@@@ -1908,7 -1902,6 +1910,7 @@@ extern int git_parse_maybe_bool(const c
  extern int git_config_int(const char *, const char *);
  extern int64_t git_config_int64(const char *, const char *);
  extern unsigned long git_config_ulong(const char *, const char *);
 +extern ssize_t git_config_ssize_t(const char *, const char *);
  extern int git_config_bool_or_int(const char *, const char *, int *);
  extern int git_config_bool(const char *, const char *);
  extern int git_config_maybe_bool(const char *, const char *);