towctrans() should return the input and set errno on failure.

POSIX says that towctrans() and towctrans_l() "return wc unchanged" on failure. We were returning 0 instead.

Technically, POSIX says that errno _may_ be set if the wctrans_t argument is invalid, which is presumably why musl/glibc do nothing. But FreeBSD (and thus iOS) set errno to EINVAL, and bionic was already setting errno to EINVAL for wctrans(), so let's be consistent with ourselves and the OS that folks are most likely to be porting code to/from.

(Noticed by inspection.)

Change-Id: I63e252d588ddfb7c6ead58d04c690d7b85f23374

Author: enh-google

libc/bionic/wctype.cpp

@@ -158,6 +158,7 @@ static wctrans_t wctrans_toupper = wctrans_t(2);
 wctrans_t wctrans(const char* name) {
   if (strcmp(name, "tolower") == 0) return wctrans_tolower;
   if (strcmp(name, "toupper") == 0) return wctrans_toupper;
+  errno = EINVAL;
   return nullptr;
 }
 
@@ -169,7 +170,7 @@ wint_t towctrans(wint_t c, wctrans_t t) {
   if (t == wctrans_tolower) return towlower(c);
   if (t == wctrans_toupper) return towupper(c);
   errno = EINVAL;
-  return 0;
+  return c;
 }
 
 wint_t towctrans_l(wint_t c, wctrans_t t, locale_t) {

tests/wctype_test.cpp

@@ -218,34 +218,64 @@ TEST(wctype, iswctype_l) {
   EXPECT_EQ(0, iswctype_l(WEOF, wctype_l("alnum", l.l), l.l));
 }
 
-TEST(wctype, towctrans) {
+TEST(wctype, wctrans) {
   EXPECT_TRUE(wctrans("tolower") != nullptr);
   EXPECT_TRUE(wctrans("toupper") != nullptr);
 
+  errno = 0;
   EXPECT_TRUE(wctrans("monkeys") == nullptr);
+  #if defined(__BIONIC__)
+  // Android/FreeBSD/iOS set errno, but musl/glibc don't.
+  EXPECT_ERRNO(EINVAL);
+  #endif
 }
 
-TEST(wctype, towctrans_l) {
+TEST(wctype, wctrans_l) {
   UtfLocale l;
   EXPECT_TRUE(wctrans_l("tolower", l.l) != nullptr);
   EXPECT_TRUE(wctrans_l("toupper", l.l) != nullptr);
 
+  errno = 0;
   EXPECT_TRUE(wctrans_l("monkeys", l.l) == nullptr);
+  #if defined(__BIONIC__)
+  // Android/FreeBSD/iOS set errno, but musl/glibc don't.
+  EXPECT_ERRNO(EINVAL);
+  #endif
 }
 
-TEST(wctype, wctrans) {
-  EXPECT_EQ(wint_t('a'), towctrans(L'A', wctrans("tolower")));
-  EXPECT_EQ(WEOF, towctrans(WEOF, wctrans("tolower")));
-
-  EXPECT_EQ(wint_t('A'), towctrans(L'a', wctrans("toupper")));
-  EXPECT_EQ(WEOF, towctrans(WEOF, wctrans("toupper")));
+TEST(wctype, towctrans) {
+  wctrans_t lower = wctrans("tolower");
+  EXPECT_EQ(wint_t('a'), towctrans(L'A', lower));
+  EXPECT_EQ(WEOF, towctrans(WEOF, lower));
+
+  wctrans_t upper = wctrans("toupper");
+  EXPECT_EQ(wint_t('A'), towctrans(L'a', upper));
+  EXPECT_EQ(WEOF, towctrans(WEOF, upper));
+
+  wctrans_t invalid = wctrans("monkeys");
+  errno = 0;
+  EXPECT_EQ(wint_t('a'), towctrans(L'a', invalid));
+  #if defined(__BIONIC__)
+  // Android/FreeBSD/iOS set errno, but musl/glibc don't.
+  EXPECT_ERRNO(EINVAL);
+  #endif
 }
 
-TEST(wctype, wctrans_l) {
+TEST(wctype, towctrans_l) {
   UtfLocale l;
-  EXPECT_EQ(wint_t('a'), towctrans_l(L'A', wctrans_l("tolower", l.l), l.l));
-  EXPECT_EQ(WEOF, towctrans_l(WEOF, wctrans_l("tolower", l.l), l.l));
-
-  EXPECT_EQ(wint_t('A'), towctrans_l(L'a', wctrans_l("toupper", l.l), l.l));
-  EXPECT_EQ(WEOF, towctrans_l(WEOF, wctrans_l("toupper", l.l), l.l));
+  wctrans_t lower = wctrans_l("tolower", l.l);
+  EXPECT_EQ(wint_t('a'), towctrans_l(L'A', lower, l.l));
+  EXPECT_EQ(WEOF, towctrans_l(WEOF, lower, l.l));
+
+  wctrans_t upper = wctrans_l("toupper", l.l);
+  EXPECT_EQ(wint_t('A'), towctrans_l(L'a', upper, l.l));
+  EXPECT_EQ(WEOF, towctrans_l(WEOF, upper, l.l));
+
+  wctrans_t invalid = wctrans_l("monkeys", l.l);
+  errno = 0;
+  EXPECT_EQ(wint_t('a'), towctrans_l(L'a', invalid, l.l));
+  #if defined(__BIONIC__)
+  // Android/FreeBSD/iOS set errno, but musl/glibc don't.
+  EXPECT_ERRNO(EINVAL);
+  #endif
 }