Add a primop for regular expression pattern matching

The function ‘builtins.match’ takes a POSIX extended regular
expression and an arbitrary string. It returns ‘null’ if the string
does not match the regular expression. Otherwise, it returns a list
containing substring matches corresponding to parenthesis groups in
the regex. The regex must match the entire string (i.e. there is an
implied "^<pat>$" around the regex).  For example:

  match "foo" "foobar" => null
  match "foo" "foo" => []
  match "f(o+)(.*)" "foooobar" => ["oooo" "bar"]
  match "(.*/)?([^/]*)" "/dir/file.nix" => ["/dir/" "file.nix"]
  match "(.*/)?([^/]*)" "file.nix" => [null "file.nix"]

The following example finds all regular files with extension .nix or
.patch underneath the current directory:

  let

    findFiles = pat: dir: concatLists (mapAttrsToList (name: type:
      if type == "directory" then
        findFiles pat (dir + "/" + name)
      else if type == "regular" && match pat name != null then
        [(dir + "/" + name)]
      else []) (readDir dir));

  in findFiles ".*\\.(nix|patch)" (toString ./.)
This commit is contained in:
Eelco Dolstra 2014-11-25 11:47:06 +01:00
parent 4e340a983f
commit 976df480c9
5 changed files with 84 additions and 5 deletions

View file

@ -1430,7 +1430,34 @@ static void prim_hashString(EvalState & state, const Pos & pos, Value * * args,
string s = state.forceString(*args[1], context, pos);
mkString(v, printHash(hashString(ht, s)), context);
};
}
/* Match a regular expression against a string and return either
null or a list containing substring matches. */
static void prim_match(EvalState & state, const Pos & pos, Value * * args, Value & v)
{
Regex regex(state.forceStringNoCtx(*args[0], pos), true);
PathSet context;
string s = state.forceString(*args[1], context, pos);
Regex::Subs subs;
if (!regex.matches(s, subs)) {
mkNull(v);
return;
}
unsigned int len = subs.empty() ? 0 : subs.rbegin()->first + 1;
state.mkList(v, len);
for (unsigned int n = 0; n < len; ++n) {
auto i = subs.find(n);
if (i == subs.end())
mkNull(*(v.list.elems[n] = state.allocValue()));
else
mkString(*(v.list.elems[n] = state.allocValue()), i->second);
}
}
/*************************************************************
@ -1584,6 +1611,7 @@ void EvalState::createBaseEnv()
addPrimOp("__unsafeDiscardStringContext", 1, prim_unsafeDiscardStringContext);
addPrimOp("__unsafeDiscardOutputDependency", 1, prim_unsafeDiscardOutputDependency);
addPrimOp("__hashString", 2, prim_hashString);
addPrimOp("__match", 2, prim_match);
// Versions
addPrimOp("__parseDrvName", 1, prim_parseDrvName);

View file

@ -1,13 +1,16 @@
#include "regex.hh"
#include "types.hh"
#include <algorithm>
namespace nix {
Regex::Regex(const string & pattern)
Regex::Regex(const string & pattern, bool subs)
{
/* Patterns must match the entire string. */
int err = regcomp(&preg, ("^(" + pattern + ")$").c_str(), REG_NOSUB | REG_EXTENDED);
if (err) throw Error(format("compiling pattern %1%: %2%") % pattern % showError(err));
int err = regcomp(&preg, ("^(" + pattern + ")$").c_str(), (subs ? 0 : REG_NOSUB) | REG_EXTENDED);
if (err) throw RegexError(format("compiling pattern %1%: %2%") % pattern % showError(err));
nrParens = subs ? std::count(pattern.begin(), pattern.end(), '(') : 0;
}
Regex::~Regex()
@ -23,6 +26,20 @@ bool Regex::matches(const string & s)
throw Error(format("matching string %1%: %2%") % s % showError(err));
}
bool Regex::matches(const string & s, Subs & subs)
{
regmatch_t pmatch[nrParens + 2];
int err = regexec(&preg, s.c_str(), nrParens + 2, pmatch, 0);
if (err == 0) {
for (unsigned int n = 2; n < nrParens + 2; ++n)
if (pmatch[n].rm_eo != -1)
subs[n - 2] = string(s, pmatch[n].rm_so, pmatch[n].rm_eo - pmatch[n].rm_so);
return true;
}
else if (err == REG_NOMATCH) return false;
throw Error(format("matching string %1%: %2%") % s % showError(err));
}
string Regex::showError(int err)
{
char buf[256];

View file

@ -5,16 +5,23 @@
#include <sys/types.h>
#include <regex.h>
#include <map>
namespace nix {
MakeError(RegexError, Error)
class Regex
{
public:
Regex(const string & pattern);
Regex(const string & pattern, bool subs = false);
~Regex();
bool matches(const string & s);
typedef std::map<unsigned int, string> Subs;
bool matches(const string & s, Subs & subs);
private:
unsigned nrParens;
regex_t preg;
string showError(int err);
};

View file

@ -0,0 +1 @@
true

View file

@ -0,0 +1,26 @@
with builtins;
let
matches = pat: s: match pat s != null;
splitFN = match "((.*)/)?([^/]*)\\.(nix|cc)";
in
assert matches "foobar" "foobar";
assert matches "fo*" "f";
assert !matches "fo+" "f";
assert matches "fo*" "fo";
assert matches "fo*" "foo";
assert matches "fo+" "foo";
assert matches "fo{1,2}" "foo";
assert !matches "fo{1,2}" "fooo";
assert !matches "fo*" "foobar";
assert match "(.*)\\.nix" "foobar.nix" == [ "foobar" ];
assert splitFN "/path/to/foobar.nix" == [ "/path/to/" "/path/to" "foobar" "nix" ];
assert splitFN "foobar.cc" == [ null null "foobar" "cc" ];
true