userdiff.c

#define USE_THE_REPOSITORY_VARIABLE
#define DISABLE_SIGN_COMPARE_WARNINGS

#include "git-compat-util.h"
#include "config.h"
#include "userdiff.h"
#include "attr.h"
#include "strbuf.h"
#include "environment.h"

static struct userdiff_driver *drivers;
static int ndrivers;
static int drivers_alloc;

#define PATTERNS(lang, rx, wrx) { \
	.name = lang, \
	.binary = -1, \
	.funcname = { \
		.pattern = rx, \
		.cflags = REG_EXTENDED, \
	}, \
	.word_regex = wrx "|[^[:space:]]|[\xc0-\xff][\x80-\xbf]+", \
	.word_regex_multi_byte = wrx "|[^[:space:]]", \
}
#define IPATTERN(lang, rx, wrx) { \
	.name = lang, \
	.binary = -1, \
	.funcname = { \
		.pattern = rx, \
		.cflags = REG_EXTENDED | REG_ICASE, \
	}, \
	.word_regex = wrx "|[^[:space:]]|[\xc0-\xff][\x80-\xbf]+", \
	.word_regex_multi_byte = wrx "|[^[:space:]]", \
}

/*
 * Built-in drivers for various languages, sorted by their names
 * (except that the "default" is left at the end).
 *
 * When writing or updating patterns, assume that the contents these
 * patterns are applied to are syntactically correct.  The patterns
 * can be simple without implementing all syntactical corner cases, as
 * long as they are sufficiently permissive.
 */
static struct userdiff_driver builtin_drivers[] = {
IPATTERN("ada",
	 "!^(.*[ \t])?(is[ \t]+new|renames|is[ \t]+separate)([ \t].*)?$\n"
	 "!^[ \t]*with[ \t].*$\n"
	 "^[ \t]*((procedure|function)[ \t]+.*)$\n"
	 "^[ \t]*((package|protected|task)[ \t]+.*)$",
	 /* -- */
	 "[a-zA-Z][a-zA-Z0-9_]*"
	 "|[-+]?[0-9][0-9#_.aAbBcCdDeEfF]*([eE][+-]?[0-9_]+)?"
	 "|=>|\\.\\.|\\*\\*|:=|/=|>=|<=|<<|>>|<>"),
PATTERNS("bash",
	 /* Optional leading indentation */
	 "^[ \t]*"
	 /* Start of captured text */
	 "("
	 "("
	     /* POSIX identifier with mandatory parentheses */
	     "[a-zA-Z_][a-zA-Z0-9_]*[ \t]*\\([ \t]*\\))"
	 "|"
	     /* Bashism identifier with optional parentheses */
	     "(function[ \t]+[a-zA-Z_][a-zA-Z0-9_]*(([ \t]*\\([ \t]*\\))|([ \t]+))"
	 ")"
	 /* Optional whitespace */
	 "[ \t]*"
	 /* Compound command starting with `{`, `(`, `((` or `[[` */
	 "(\\{|\\(\\(?|\\[\\[)"
	 /* End of captured text */
	 ")",
	 /* -- */
	 /* Characters not in the default $IFS value */
	 "[^ \t]+"),
PATTERNS("bibtex",
	 "(@[a-zA-Z]{1,}[ \t]*\\{{0,1}[ \t]*[^ \t\"@',\\#}{~%]*).*$",
	 /* -- */
	 "[={}\"]|[^={}\" \t]+"),
PATTERNS("cpp",
	 /* Jump targets or access declarations */
	 "!^[ \t]*[A-Za-z_][A-Za-z_0-9]*:[[:space:]]*($|/[/*])\n"
	 /* functions/methods, variables, and compounds at top level */
	 "^((::[[:space:]]*)?[A-Za-z_].*)$",
	 /* -- */
	 /* identifiers and keywords */
	 "[a-zA-Z_][a-zA-Z0-9_]*"
	 /* decimal and octal integers as well as floatingpoint numbers */
	 "|[0-9][0-9.]*([Ee][-+]?[0-9]+)?[fFlLuU]*"
	 /* hexadecimal and binary integers */
	 "|0[xXbB][0-9a-fA-F]+[lLuU]*"
	 /* floatingpoint numbers that begin with a decimal point */
	 "|\\.[0-9][0-9]*([Ee][-+]?[0-9]+)?[fFlL]?"
	 "|[-+*/<>%&^|=!]=|--|\\+\\+|<<=?|>>=?|&&|\\|\\||::|->\\*?|\\.\\*|<=>"),
PATTERNS("csharp",
	 /*
	  * Jump over reserved keywords which are illegal method names, but which
	  * can be followed by parentheses without special characters in between,
	  * making them look like methods.
	  */
	 "!(^|[ \t]+)" /* Start of line or whitespace. */
		"(do|while|for|foreach|if|else|new|default|return|switch|case|throw"
		"|catch|using|lock|fixed)"
		"([ \t(]+|$)\n" /* Whitespace, "(", or end of line. */
	 /*
	  * Methods/constructors:
	  * The strategy is to identify a minimum of two groups (any combination
	  * of keywords/type/name) before the opening parenthesis, and without
	  * final unexpected characters, normally only used in ordinary statements.
	  */
	 "^[ \t]*" /* Remove leading whitespace. */
		"(" /* Start chunk header capture. */
		"(" /* First group. */
			"[][[:alnum:]@_.]" /* Name. */
			"(<[][[:alnum:]@_, \t<>]+>)?" /* Optional generic parameters. */
		")+"
		"([ \t]+" /* Subsequent groups, prepended with space. */
			"([][[:alnum:]@_.](<[][[:alnum:]@_, \t<>]+>)?)+"
		")+"
		"[ \t]*" /* Optional space before parameters start. */
		"\\(" /* Start of method parameters. */
		"[^;]*" /* Allow complex parameters, but exclude statements (;). */
		")$\n" /* Close chunk header capture. */
	 /*
	  * Properties:
	  * As with methods, expect a minimum of two groups. But, more trivial than
	  * methods, the vast majority of properties long enough to be worth
	  * showing a chunk header for don't include "=:;,()" on the line they are
	  * defined, since they don't have a parameter list.
	  */
	 "^[ \t]*("
		"([][[:alnum:]@_.](<[][[:alnum:]@_, \t<>]+>)?)+"
		"([ \t]+"
			"([][[:alnum:]@_.](<[][[:alnum:]@_, \t<>]+>)?)+"
		")+" /* Up to here, same as methods regex. */
		"[^;=:,()]*" /* Compared to methods, no parameter list allowed. */
		")$\n"
	 /* Type definitions */
	 "^[ \t]*(((static|public|internal|private|protected|new|unsafe|sealed|abstract|partial)[ \t]+)*(class|enum|interface|struct|record)[ \t]+.*)$\n"
	 /* Namespace */
	 "^[ \t]*(namespace[ \t]+.*)$",
	 /* -- */
	 "[a-zA-Z_][a-zA-Z0-9_]*"
	 "|[-+0-9.e]+[fFlL]?|0[xXbB]?[0-9a-fA-F]+[lL]?"
	 "|[-+*/<>%&^|=!]=|--|\\+\\+|<<=?|>>=?|&&|\\|\\||::|->"),
IPATTERN("css",
	 "![:;][[:space:]]*$\n"
	 "^[:[@.#]?[_a-z0-9].*$",
	 /* -- */
	 /*
	  * This regex comes from W3C CSS specs. Should theoretically also
	  * allow ISO 10646 characters U+00A0 and higher,
	  * but they are not handled in this regex.
	  */
	 "-?[_a-zA-Z][-_a-zA-Z0-9]*" /* identifiers */
	 "|-?[0-9]+|\\#[0-9a-fA-F]+" /* numbers */
),
PATTERNS("dts",
	 "!;\n"
	 "!=\n"
	 /* lines beginning with a word optionally preceded by '&' or the root */
	 "^[ \t]*((/[ \t]*\\{|&?[a-zA-Z_]).*)",
	 /* -- */
	 /* Property names and math operators */
	 "[a-zA-Z0-9,._+?#-]+"
	 "|[-+*/%&^|!~]|>>|<<|&&|\\|\\|"),
PATTERNS("elixir",
	 "^[ \t]*((def(macro|module|impl|protocol|p)?|test)[ \t].*)$",
	 /* -- */
	 /* Atoms, names, and module attributes */
	 "[@:]?[a-zA-Z0-9@_?!]+"
	 /* Numbers with specific base */
	 "|[-+]?0[xob][0-9a-fA-F]+"
	 /* Numbers */
	 "|[-+]?[0-9][0-9_.]*([eE][-+]?[0-9_]+)?"
	 /* Operators and atoms that represent them */
	 "|:?(\\+\\+|--|\\.\\.|~~~|<>|\\^\\^\\^|<?\\|>|<<<?|>?>>|<<?~|~>?>|<~>|<=|>=|===?|!==?|=~|&&&?|\\|\\|\\|?|=>|<-|\\\\\\\\|->)"
	 /* Not real operators, but should be grouped */
	 "|:?%[A-Za-z0-9_.]\\{\\}?"),
IPATTERN("fortran",
	 /* Don't match comment lines */
	 "!^([C*]|[ \t]*!)\n"
	 /* Don't match 'module procedure' lines */
	 "!^[ \t]*MODULE[ \t]+PROCEDURE[ \t]\n"
	 /* Program, module, block data */
	 "^[ \t]*((END[ \t]+)?(PROGRAM|MODULE|BLOCK[ \t]+DATA"
		/* Subroutines and functions */
		"|([^!'\" \t]+[ \t]+)*(SUBROUTINE|FUNCTION))[ \t]+[A-Z].*)$",
	 /* -- */
	 "[a-zA-Z][a-zA-Z0-9_]*"
	 "|\\.([Ee][Qq]|[Nn][Ee]|[Gg][TtEe]|[Ll][TtEe]|[Tt][Rr][Uu][Ee]|[Ff][Aa][Ll][Ss][Ee]|[Aa][Nn][Dd]|[Oo][Rr]|[Nn]?[Ee][Qq][Vv]|[Nn][Oo][Tt])\\."
	 /* numbers and format statements like 2E14.4, or ES12.6, 9X.
	  * Don't worry about format statements without leading digits since
	  * they would have been matched above as a variable anyway. */
	 "|[-+]?[0-9.]+([AaIiDdEeFfLlTtXx][Ss]?[-+]?[0-9.]*)?(_[a-zA-Z0-9][a-zA-Z0-9_]*)?"
	 "|//|\\*\\*|::|[/<>=]="),
IPATTERN("fountain",
	 "^((\\.[^.]|(int|ext|est|int\\.?/ext|i/e)[. ]).*)$",
	 /* -- */
	 "[^ \t-]+"),
PATTERNS("golang",
	 /* Functions */
	 "^[ \t]*(func[ \t]*.*(\\{[ \t]*)?)\n"
	 /* Structs and interfaces */
	 "^[ \t]*(type[ \t].*(struct|interface)[ \t]*(\\{[ \t]*)?)",
	 /* -- */
	 "[a-zA-Z_][a-zA-Z0-9_]*"
	 "|[-+0-9.eE]+i?|0[xX]?[0-9a-fA-F]+i?"
	 "|[-+*/<>%&^|=!:]=|--|\\+\\+|<<=?|>>=?|&\\^=?|&&|\\|\\||<-|\\.{3}"),
PATTERNS("html",
	 "^[ \t]*(<[Hh][1-6]([ \t].*)?>.*)$",
	 /* -- */
	 "[^<>= \t]+"),
PATTERNS("java",
	 "!^[ \t]*(catch|do|for|if|instanceof|new|return|switch|throw|while)\n"
	 /* Class, enum, interface, and record declarations */
	 "^[ \t]*(([a-z-]+[ \t]+)*(class|enum|interface|record)[ \t]+.*)$\n"
	 /* Method definitions; note that constructor signatures are not */
	 /* matched because they are indistinguishable from method calls. */
	 "^[ \t]*(([A-Za-z_<>&][][?&<>.,A-Za-z_0-9]*[ \t]+)+[A-Za-z_][A-Za-z_0-9]*[ \t]*\\([^;]*)$",
	 /* -- */
	 "[a-zA-Z_][a-zA-Z0-9_]*"
	 "|[-+0-9.e]+[fFlL]?|0[xXbB]?[0-9a-fA-F]+[lL]?"
	 "|[-+*/<>%&^|=!]="
	 "|--|\\+\\+|<<=?|>>>?=?|&&|\\|\\|"),
PATTERNS("kotlin",
	 "^[ \t]*(([a-z]+[ \t]+)*(fun|class|interface)[ \t]+.*)$",
	 /* -- */
	 "[a-zA-Z_][a-zA-Z0-9_]*"
	 /* hexadecimal and binary numbers */
	 "|0[xXbB][0-9a-fA-F_]+[lLuU]*"
	 /* integers and floats */
	 "|[0-9][0-9_]*([.][0-9_]*)?([Ee][-+]?[0-9]+)?[fFlLuU]*"
	 /* floating point numbers beginning with decimal point */
	 "|[.][0-9][0-9_]*([Ee][-+]?[0-9]+)?[fFlLuU]?"
	 /* unary and binary operators */
	 "|[-+*/<>%&^|=!]==?|--|\\+\\+|<<=|>>=|&&|\\|\\||->|\\.\\*|!!|[?:.][.:]"),
PATTERNS("markdown",
	 "^ {0,3}#{1,6}[ \t].*",
	 /* -- */
	 "[^<>= \t]+"),
PATTERNS("matlab",
	 /*
	  * Octave pattern is mostly the same as matlab, except that '%%%' and
	  * '##' can also be used to begin code sections, in addition to '%%'
	  * that is understood by both.
	  */
	 "^[[:space:]]*((classdef|function)[[:space:]].*)$|^(%%%?|##)[[:space:]].*$",
	 /* -- */
	 "[a-zA-Z_][a-zA-Z0-9_]*|[-+0-9.e]+|[=~<>]=|\\.[*/\\^']|\\|\\||&&"),
PATTERNS("objc",
	 /* Negate C statements that can look like functions */
	 "!^[ \t]*(do|for|if|else|return|switch|while)\n"
	 /* Objective-C methods */
	 "^[ \t]*([-+][ \t]*\\([ \t]*[A-Za-z_][A-Za-z_0-9* \t]*\\)[ \t]*[A-Za-z_].*)$\n"
	 /* C functions */
	 "^[ \t]*(([A-Za-z_][A-Za-z_0-9]*[ \t]+)+[A-Za-z_][A-Za-z_0-9]*[ \t]*\\([^;]*)$\n"
	 /* Objective-C class/protocol definitions */
	 "^(@(implementation|interface|protocol)[ \t].*)$",
	 /* -- */
	 "[a-zA-Z_][a-zA-Z0-9_]*"
	 "|[-+0-9.e]+[fFlL]?|0[xXbB]?[0-9a-fA-F]+[lL]?"
	 "|[-+*/<>%&^|=!]=|--|\\+\\+|<<=?|>>=?|&&|\\|\\||::|->"),
PATTERNS("pascal",
	 "^(((class[ \t]+)?(procedure|function)|constructor|destructor|interface"
	 "|implementation|initialization|finalization)[ \t]*.*)$\n"
	 "^(.*=[ \t]*(class|record).*)$",
	 /* -- */
	 "[a-zA-Z_][a-zA-Z0-9_]*"
	 "|[-+0-9.e]+|0[xXbB]?[0-9a-fA-F]+"
	 "|<>|<=|>=|:=|\\.\\."),
PATTERNS("perl",
	 "^package .*\n"
	 "^sub [[:alnum:]_':]+[ \t]*"
		"(\\([^)]*\\)[ \t]*)?" /* prototype */
		/*
		 * Attributes.  A regex can't count nested parentheses,
		 * so just slurp up whatever we see, taking care not
		 * to accept lines like "sub foo; # defined elsewhere".
		 *
		 * An attribute could contain a semicolon, but at that
		 * point it seems reasonable enough to give up.
		 */
		"(:[^;#]*)?"
		"(\\{[ \t]*)?" /* brace can come here or on the next line */
		"(#.*)?$\n" /* comment */
	 "^(BEGIN|END|INIT|CHECK|UNITCHECK|AUTOLOAD|DESTROY)[ \t]*"
		"(\\{[ \t]*)?" /* brace can come here or on the next line */
		"(#.*)?$\n"
	 "^=head[0-9] .*",	/* POD */
	 /* -- */
	 "[[:alpha:]_'][[:alnum:]_']*"
	 "|0[xb]?[0-9a-fA-F_]*"
	 /* taking care not to interpret 3..5 as (3.)(.5) */
	 "|[0-9a-fA-F_]+(\\.[0-9a-fA-F_]+)?([eE][-+]?[0-9_]+)?"
	 "|=>|-[rwxoRWXOezsfdlpSugkbctTBMAC>]|~~|::"
	 "|&&=|\\|\\|=|//=|\\*\\*="
	 "|&&|\\|\\||//|\\+\\+|--|\\*\\*|\\.\\.\\.?"
	 "|[-+*/%.^&<>=!|]="
	 "|=~|!~"
	 "|<<|<>|<=>|>>"),
PATTERNS("php",
	 "^[\t ]*(((public|protected|private|static|abstract|final)[\t ]+)*function.*)$\n"
	 "^[\t ]*((((final|abstract)[\t ]+)?class|enum|interface|trait).*)$",
	 /* -- */
	 "[a-zA-Z_][a-zA-Z0-9_]*"
	 "|[-+0-9.e]+|0[xXbB]?[0-9a-fA-F]+"
	 "|[-+*/<>%&^|=!.]=|--|\\+\\+|<<=?|>>=?|===|&&|\\|\\||::|->"),
PATTERNS("python",
	 "^[ \t]*((class|(async[ \t]+)?def)[ \t].*)$",
	 /* -- */
	 "[a-zA-Z_][a-zA-Z0-9_]*"
	 "|[-+0-9.e]+[jJlL]?|0[xX]?[0-9a-fA-F]+[lL]?"
	 "|[-+*/<>%&^|=!]=|//=?|<<=?|>>=?|\\*\\*=?"),
	 /* -- */
PATTERNS("ruby",
	 "^[ \t]*((class|module|def)[ \t].*)$",
	 /* -- */
	 "(@|@@|\\$)?[a-zA-Z_][a-zA-Z0-9_]*"
	 "|[-+0-9.e]+|0[xXbB]?[0-9a-fA-F]+|\\?(\\\\C-)?(\\\\M-)?."
	 "|//=?|[-+*/<>%&^|=!]=|<<=?|>>=?|===|\\.{1,3}|::|[!=]~"),
PATTERNS("rust",
	 "^[\t ]*((pub(\\([^\\)]+\\))?[\t ]+)?((async|const|unsafe|extern([\t ]+\"[^\"]+\"))[\t ]+)?(struct|enum|union|mod|trait|fn|impl|macro_rules!)[< \t]+[^;]*)$",
	 /* -- */
	 "[a-zA-Z_][a-zA-Z0-9_]*"
	 "|[0-9][0-9_a-fA-Fiosuxz]*(\\.([0-9]*[eE][+-]?)?[0-9_fF]*)?"
	 "|[-+*\\/<>%&^|=!:]=|<<=?|>>=?|&&|\\|\\||->|=>|\\.{2}=|\\.{3}|::"),
PATTERNS("scheme",
	 "^[\t ]*(\\(((define|def(struct|syntax|class|method|rules|record|proto|alias)?)[-*/ \t]|(library|module|struct|class)[*+ \t]).*)$",
	 /*
	  * R7RS valid identifiers include any sequence enclosed
	  * within vertical lines having no backslashes
	  */
	 "\\|([^\\\\]*)\\|"
	 /* All other words should be delimited by spaces or parentheses */
	 "|([^][)(}{[ \t])+"),
PATTERNS("tex", "^(\\\\((sub)*section|chapter|part)\\*{0,1}\\{.*)$",
	 "\\\\[a-zA-Z@]+|\\\\.|([a-zA-Z0-9]|[^\x01-\x7f])+"),
{ .name = "default", .binary = -1 },
};
#undef PATTERNS
#undef IPATTERN

static struct userdiff_driver driver_true = {
	.name = "diff=true",
	.binary = 0,
};

static struct userdiff_driver driver_false = {
	.name = "!diff",
	.binary = 1,
};

struct find_by_namelen_data {
	const char *name;
	size_t len;
	struct userdiff_driver *driver;
};

static int userdiff_find_by_namelen_cb(struct userdiff_driver *driver,
				       enum userdiff_driver_type type UNUSED,
				       void *priv)
{
	struct find_by_namelen_data *cb_data = priv;

	if (!xstrncmpz(driver->name, cb_data->name, cb_data->len)) {
		cb_data->driver = driver;
		return 1; /* tell the caller to stop iterating */
	}
	return 0;
}

static int regexec_supports_multi_byte_chars(void)
{
	static const char not_space[] = "[^[:space:]]";
	static const char utf8_multi_byte_char[] = "\xc2\xa3";
	regex_t re;
	regmatch_t match;
	static int result = -1;

	if (result != -1)
		return result;
	if (regcomp(&re, not_space, REG_EXTENDED))
		BUG("invalid regular expression: %s", not_space);
	result = !regexec(&re, utf8_multi_byte_char, 1, &match, 0) &&
		match.rm_so == 0 &&
		match.rm_eo == strlen(utf8_multi_byte_char);
	regfree(&re);
	return result;
}

static struct userdiff_driver *userdiff_find_by_namelen(const char *name, size_t len)
{
	struct find_by_namelen_data udcbdata = {
		.name = name,
		.len = len,
	};
	for_each_userdiff_driver(userdiff_find_by_namelen_cb, &udcbdata);
	return udcbdata.driver;
}

static int parse_funcname(struct userdiff_funcname *f, const char *k,
		const char *v, int cflags)
{
	f->pattern = NULL;
	FREE_AND_NULL(f->pattern_owned);
	if (git_config_string(&f->pattern_owned, k, v) < 0)
		return -1;
	f->pattern = f->pattern_owned;
	f->cflags = cflags;
	return 0;
}

static int parse_tristate(int *b, const char *k, const char *v)
{
	if (v && !strcasecmp(v, "auto"))
		*b = -1;
	else
		*b = git_config_bool(k, v);
	return 0;
}

static int parse_bool(int *b, const char *k, const char *v)
{
	*b = git_config_bool(k, v);
	return 0;
}

int userdiff_config(const char *k, const char *v)
{
	struct userdiff_driver *drv;
	const char *name, *type;
	size_t namelen;

	if (parse_config_key(k, "diff", &name, &namelen, &type) || !name)
		return 0;

	drv = userdiff_find_by_namelen(name, namelen);
	if (!drv) {
		ALLOC_GROW(drivers, ndrivers+1, drivers_alloc);
		drv = &drivers[ndrivers++];
		memset(drv, 0, sizeof(*drv));
		drv->name = xmemdupz(name, namelen);
		drv->binary = -1;
	}

	if (!strcmp(type, "funcname"))
		return parse_funcname(&drv->funcname, k, v, 0);
	if (!strcmp(type, "xfuncname"))
		return parse_funcname(&drv->funcname, k, v, REG_EXTENDED);
	if (!strcmp(type, "binary"))
		return parse_tristate(&drv->binary, k, v);
	if (!strcmp(type, "command")) {
		FREE_AND_NULL(drv->external.cmd);
		return git_config_string(&drv->external.cmd, k, v);
	}
	if (!strcmp(type, "trustexitcode")) {
		drv->external.trust_exit_code = git_config_bool(k, v);
		return 0;
	}
	if (!strcmp(type, "textconv")) {
		int ret;
		FREE_AND_NULL(drv->textconv_owned);
		ret = git_config_string(&drv->textconv_owned, k, v);
		drv->textconv = drv->textconv_owned;
		return ret;
	}
	if (!strcmp(type, "cachetextconv"))
		return parse_bool(&drv->textconv_want_cache, k, v);
	if (!strcmp(type, "wordregex")) {
		int ret;
		FREE_AND_NULL(drv->word_regex_owned);
		ret = git_config_string(&drv->word_regex_owned, k, v);
		drv->word_regex = drv->word_regex_owned;
		return ret;
	}
	if (!strcmp(type, "algorithm")) {
		int ret;
		FREE_AND_NULL(drv->algorithm_owned);
		ret = git_config_string(&drv->algorithm_owned, k, v);
		drv->algorithm = drv->algorithm_owned;
		return ret;
	}

	return 0;
}

struct userdiff_driver *userdiff_find_by_name(const char *name)
{
	int len = strlen(name);
	struct userdiff_driver *driver = userdiff_find_by_namelen(name, len);
	if (driver && driver->word_regex_multi_byte) {
		if (regexec_supports_multi_byte_chars())
			driver->word_regex = driver->word_regex_multi_byte;
		driver->word_regex_multi_byte = NULL;
	}
	return driver;
}

struct userdiff_driver *userdiff_find_by_path(struct index_state *istate,
					      const char *path)
{
	static struct attr_check *check;

	if (!check)
		check = attr_check_initl("diff", NULL);
	if (!path)
		return NULL;
	git_check_attr(istate, path, check);

	if (ATTR_TRUE(check->items[0].value))
		return &driver_true;
	if (ATTR_FALSE(check->items[0].value))
		return &driver_false;
	if (ATTR_UNSET(check->items[0].value))
		return NULL;
	return userdiff_find_by_name(check->items[0].value);
}

struct userdiff_driver *userdiff_get_textconv(struct repository *r,
					      struct userdiff_driver *driver)
{
	if (!driver->textconv)
		return NULL;

	if (driver->textconv_want_cache && !driver->textconv_cache &&
	    have_git_dir()) {
		struct notes_cache *c = xmalloc(sizeof(*c));
		struct strbuf name = STRBUF_INIT;

		strbuf_addf(&name, "textconv/%s", driver->name);
		notes_cache_init(r, c, name.buf, driver->textconv);
		driver->textconv_cache = c;
		strbuf_release(&name);
	}

	return driver;
}

static int for_each_userdiff_driver_list(each_userdiff_driver_fn fn,
					 enum userdiff_driver_type type, void *cb_data,
					 struct userdiff_driver *drv,
					 int drv_size)
{
	int i;
	int ret;
	for (i = 0; i < drv_size; i++) {
		struct userdiff_driver *item = drv + i;
		if ((ret = fn(item, type, cb_data)))
			return ret;
	}
	return 0;
}

int for_each_userdiff_driver(each_userdiff_driver_fn fn, void *cb_data)
{
	int ret;

	ret = for_each_userdiff_driver_list(fn, USERDIFF_DRIVER_TYPE_CUSTOM,
					    cb_data, drivers, ndrivers);
	if (ret)
		return ret;

	ret = for_each_userdiff_driver_list(fn, USERDIFF_DRIVER_TYPE_BUILTIN,
					    cb_data, builtin_drivers,
					    ARRAY_SIZE(builtin_drivers));
	if (ret)
		return ret;

	return 0;
}