bug#24603: [PATCHv5 11/11] Implement Irish casing rules (bug#24603)

[Michal Nazarewicz <mina86@mina86.com>]

Add rules for casing Irish words whose rules are quite complicated
and require some letters to remain lower case when upper casing,
involve insertion of dashes and various other transformations.

* src/casefiddle.c (struct casing_context): Add flags for denoting
Irish casing rules are in effect.
(prepare_casing_context): Detect Irish language and set ctx->special
accordingly.
(irish_upcase, irish_downcase): New functions for upcasing and
downcasing Irish letters.
(is_irish_vowel, is_irish_uc_vowel, is_irish_lc_vowel): New functions
detecting whether a letter is an Irish vowel.
(maybe_case_irish): New function implementing Irish casing rules.
(case_characters): Make use of maybe_case_irish.

* test/src/casefiddle-resources/irish-lowercase-1.txt,
test/src/casefiddle-resources/irish-lowercase-1-ref.txt,
test/src/casefiddle-resources/irish-uppercase-1.txt,
test/src/casefiddle-resources/irish-uppercase-1-ref.txt: New files
with test cases for Irish capitalisation.  The files are copied from
Mozilla’s test suite.

* test/src/casefiddle-tests.el (casefiddle-tests--resources-dir): New
variable to point to aforementioned test case files.
(casefiddle-tests--test-casing): Support missing expected strings.
(casefiddle--read-lines): New helper functions for reading lines from
a file.
(casefiddle-test-irish): Apply test cases reada from the Irish test
case files.
---
 src/casefiddle.c                                   | 313 +++++++++++++++++++++
 .../casefiddle-resources/irish-lowercase-1-ref.txt | 211 ++++++++++++++
 .../src/casefiddle-resources/irish-lowercase-1.txt | 211 ++++++++++++++
 .../casefiddle-resources/irish-uppercase-1-ref.txt | 105 +++++++
 .../src/casefiddle-resources/irish-uppercase-1.txt | 105 +++++++
 test/src/casefiddle-tests.el                       |  58 +++-
 6 files changed, 992 insertions(+), 11 deletions(-)
 create mode 100644 test/src/casefiddle-resources/irish-lowercase-1-ref.txt
 create mode 100644 test/src/casefiddle-resources/irish-lowercase-1.txt
 create mode 100644 test/src/casefiddle-resources/irish-uppercase-1-ref.txt
 create mode 100644 test/src/casefiddle-resources/irish-uppercase-1.txt

diff --git a/src/casefiddle.c b/src/casefiddle.c
index a33bac7d21e..3352fb6795a 100644
--- a/src/casefiddle.c
+++ b/src/casefiddle.c
@@ -86,6 +86,24 @@ struct casing_context {
     /* As above plus look out for diacritics combining above because
        we may need to inject dot above before them. */
     SPECIAL_LT_INS_DOT_ABOVE,
+
+    /* Flags for Irish word capitalising rules.  Those are insane, see
+       https://bugzilla.mozilla.org/show_bug.cgi?id=1018805 and
+       https://bugzilla.mozilla.org/show_bug.cgi?id=1014639 for reference. */
+    /* Irish handling enabled; we are lower-casing words. */
+    SPECIAL_GA_LC,
+    /* Irish handling enabled; we are upper-casing words or capitalising. */
+    SPECIAL_GA_UC,
+    /* Upper-case next character. */
+    SPECIAL_GA_UC_NEXT,
+    /* We’re in the middle of a potential ‘bhf’ or ‘bhF’ triplet. */
+    SPECIAL_GA_TRIPLET_B = 'b',
+    /* We’re in the middle of a potential ‘n-{v}’ triplet. */
+    SPECIAL_GA_TRIPLET_N = 'n',
+    /* We’re in the middle of a potential triplet starting with ‘ts’ or ‘tS’. */
+    SPECIAL_GA_TRIPLET_T = 't'
+    /* Yes, it matters that the last three flags equal the characters for b,
+       n or t. */
   } special;
 };
 
@@ -127,6 +145,9 @@ prepare_casing_context (struct casing_context *ctx,
       break;
     case ('l' << 8) | 't':  /* Lithuania */
       ctx->special = SPECIAL_LT;
+      break;
+    case ('g' << 8) | 'a':  /* Irish */
+      ctx->special = flag == CASE_DOWN ? SPECIAL_GA_LC : SPECIAL_GA_UC;
     }
 }
 
@@ -509,6 +530,289 @@ maybe_case_lithuanian (struct casing_str_buf *buf, struct casing_context *ctx,
   return RES_NOT_TOUCHED;
 }
 \f
+/* The naïve method works for ASCII letters but also non-ASCII Irish
+   vowels and second byte in UTF-8 representation of those vowels. */
+static int irish_upcase(int ch) { return ch & ~('a' ^ 'A'); }
+static int irish_downcase(int ch) { return ch | ('a' ^ 'A'); }
+
+/* A byte starting two-byte sequence of non-ASCII Irish vowels. */
+#define GA_UTF8_FIRST_BYTE 0xC3
+
+/* Classifies UTF-8 encoded character at *CH as Irish vowel or not. */
+static enum {
+  GA_NOT_VOWEL = 0,
+  GA_UC_VOWEL = 1,
+  GA_LC_VOWEL = 2
+} is_irish_vowel(const unsigned char *ch) {
+  switch (*ch) {
+  case 'A': case 'E': case 'I': case 'O': case 'U':
+    return GA_UC_VOWEL;
+  case 'a': case 'e': case 'i': case 'o': case 'u':
+    return GA_LC_VOWEL;
+  case GA_UTF8_FIRST_BYTE:
+    switch (ch[1]) {
+    case 0x81:  /* C3 81 → U+00C1 → Á */
+    case 0x89:  /* C3 89 → U+00C9 → É */
+    case 0x8D:  /* C3 8D → U+00CD → Í */
+    case 0x93:  /* C3 93 → U+00D3 → Ó */
+    case 0x9A:  /* C3 9A → U+00DA → Ú */
+      return GA_UC_VOWEL;
+    case 0xA1:  /* C3 A1 → U+00E1 → á */
+    case 0xA9:  /* C3 A9 → U+00E9 → é */
+    case 0xAD:  /* C3 AD → U+00ED → í */
+    case 0xB3:  /* C3 B3 → U+00F3 → ó */
+    case 0xBA:  /* C3 BA → U+00FA → ú */
+      return GA_LC_VOWEL;
+    }
+  }
+  return GA_NOT_VOWEL;
+}
+
+/* Return whether *CH is an upper-case Irish vowel encoded in UTF-8. */
+static bool
+is_irish_uc_vowel(const char *ch) {
+  return is_irish_vowel(ch) == GA_UC_VOWEL;
+}
+
+/* Return whether *CH is an lower-case Irish vowel encoded in UTF-8. */
+static bool
+is_irish_lc_vowel(const char *ch) {
+  return is_irish_vowel(ch) == GA_LC_VOWEL;
+}
+
+/* Save in BUF result of casing character CH if Irish casing rules apply.
+
+   If not-NULL, NEXT points to the next character in the cased string.  If NULL,
+   it is assumed current character is the last one being cased.  This is used to
+   apply some rules which depend on proceeding state.
+
+   FLAG is a normalised flag (as returned by normalise_flag function).
+
+   Return -2 (RES_NOT_TOUCHED) if Irish rules did not apply, no changes
+   were made and other casing rules should be tried.  Otherwise, meaning of
+   return values is the same as in case_characters function. */
+static int
+maybe_case_irish (struct casing_str_buf *buf, struct casing_context *ctx,
+		  enum case_action flag, int ch, const unsigned char *next) {
+  unsigned n;
+
+  switch (ctx->special) {
+  case SPECIAL_GA_LC:
+    /* We are lower-casing words and Irish rules are enabled.  See
+       https://bugzilla.mozilla.org/show_bug.cgi?id=1018805 for reference.  The
+       rules are:
+
+         t{V} → t-{v}
+         n{V} → n-{v}
+
+       {V} denotes upper-case Irish vowel and {v} denotes a lower-case one. */
+
+    if (!next ||
+	ctx->inword ||
+	(ch != 't' && ch != 'n') ||
+	!is_irish_uc_vowel(next))
+      return RES_NOT_TOUCHED;
+
+    ctx->inword = true;
+    buf->len_chars = 3;
+    buf->data[0] = ch;
+    buf->data[1] = '-';
+    if (*next < 0x80) {
+      buf->data[2] = irish_downcase(next[0]);
+      buf->len_bytes = 3;
+      return 1;
+    } else {
+      buf->data[2] = next[0];
+      buf->data[3] = irish_downcase(next[1]);
+      buf->len_bytes = 4;
+      return 2;
+    }
+
+  case SPECIAL_GA_UC:
+    /* We are upper-casing or capitalising words and Irish rules are enabled.
+       See https://bugzilla.mozilla.org/show_bug.cgi?id=1014639 for
+       reference. The rules are:
+
+	 h{V}  → h{V}
+	 n{V}  → n{V}
+	 t{V}  → t{V}
+
+	 bp    → bP
+	 bP    → bP
+	 dt    → dT
+	 dT    → dT
+	 gc    → gC
+	 gC    → gC
+	 mb    → mB
+	 mB    → mB
+	 nd    → nD
+	 nD    → nD
+	 ng    → nG
+	 nG    → nG
+
+	 bhf   → bhF
+	 bhF   → bhF
+
+	 n-{v} → n{V}
+	 t-{v} → t{V}
+
+	 tSL   → tSL
+	 tSl   → tSL
+	 tsl   → tSL
+	 tSN   → tSN
+	 tsn   → tSN
+	 tSn   → tSN
+	 tSR   → tSR
+	 tSr   → tSR
+	 tsr   → tSR
+	 tS{V} → tS{V}
+	 tS{v} → tS{V}
+	 ts{v} → tS{V}
+
+       {V} denotes upper-case Irish vowel and {v} denotes a lower-case one. */
+
+    if (!next || ctx->inword || ch < 'a' || ch > 'z')
+      return RES_NOT_TOUCHED;
+
+    n = irish_upcase(*next);
+    if (((ch == 'h' || ch == 'n' || ch == 't') && is_irish_uc_vowel(next)) ||
+	(ch == 'b' && n == 'P') ||
+	(ch == 'd' && n == 'T') ||
+	(ch == 'g' && n == 'C') ||
+	(ch == 'm' && n == 'B') ||
+	(ch == 'n' && n == 'D') ||
+	(ch == 'n' && n == 'G'))
+      {
+	ctx->inword = true;
+	ctx->special = SPECIAL_GA_UC_NEXT;
+	buf->data[0] = ch;
+	buf->len_chars = 1;
+	buf->len_bytes = 1;
+	return RES_NO_CHANGE;
+      }
+
+    if ((ch == 'b' && *next == 'h') || (ch == 't' && n == 'S') ||
+	(ch == 't' && *next == '-') || (ch == 'n' && *next == '-'))
+      {
+	/* We can only look at two characters at a time but here we need to make
+	   a decision based on a 3-character sequence.
+
+	   Let’s return empty string for now, remember the current character and
+	   when we’ll be dealing with the next character we’ll be able to see
+	   three characters.
+
+	   Downside of this approach is that we cannot always correctly mark
+	   buffer as changed.  Namely, ‘bhF’ triplet does not need to be changed
+	   but sadly we'll mark this as modified. */
+	ctx->inword = true;
+	ctx->special = ch;
+	buf->len_chars = 0;
+	buf->len_bytes = 0;
+	return RES_CHANGED;
+      }
+
+    return RES_NOT_TOUCHED;
+
+  case SPECIAL_GA_UC_NEXT:
+    ctx->special = SPECIAL_GA_UC;
+    n = irish_upcase(ch);
+    buf->len_bytes = CHAR_STRING (n, buf->data);
+    buf->len_chars = 1;
+    return n == ch ? RES_NO_CHANGE : RES_CHANGED;
+
+  case SPECIAL_GA_TRIPLET_B:
+  case SPECIAL_GA_TRIPLET_N:
+  case SPECIAL_GA_TRIPLET_T:
+    /* We’re here after encountering a possible beginning of a three-character
+       sequence that needs to be handled.  Those are:
+
+	 bhf   → bhF
+	 bhF   → bhF
+
+	 n-{v} → n{V}
+	 t-{v} → t{V}
+
+	 tSL   → tSL
+	 tSl   → tSL
+	 tsl   → tSL
+	 tSN   → tSN
+	 tsn   → tSN
+	 tSn   → tSN
+	 tSR   → tSR
+	 tSr   → tSR
+	 tsr   → tSR
+	 tS{V} → tS{V}
+	 tS{v} → tS{V}
+	 ts{v} → tS{V} */
+
+    if (*next)
+      switch (ch) {
+      case '-':  /* ‘n-’ or ‘t-’ prefix. */
+	if (is_irish_lc_vowel(next))
+	  {
+	    buf->data[0] = ctx->special;
+	    buf->len_chars = 1;
+	    buf->len_bytes = 1;
+	    ctx->special = SPECIAL_GA_UC_NEXT;
+	    return RES_CHANGED;
+	  }
+	break;
+
+      case 'h':  /* ‘bh’ prefix */
+	if (irish_upcase(*next) == 'F') {
+	  ctx->special = SPECIAL_GA_UC;
+	  buf->data[0] = 'b';
+	  buf->data[1] = 'h';
+	  buf->data[2] = 'F';
+	  buf->len_chars = 3;
+	  buf->len_bytes = 3;
+	  return 1;
+	}
+	break;
+
+      case 's':  /* ‘ts’ prefix. */
+	if (*next == 'l' || *next == 'n' || *next == 'r' ||
+	    is_irish_lc_vowel(next))
+	  goto tSU;
+	break;
+
+      case 'S':  /* ‘tS’ prefix. */
+	if (*next == 'l' || *next == 'n' || *next == 'r' ||
+	    *next == 'L' || *next == 'N' || *next == 'R' ||
+	    is_irish_vowel(next))
+	  {
+	  tSU:
+	    /* t{s}{x} → tS{X} */
+	    ctx->special = SPECIAL_GA_UC_NEXT;
+	    buf->data[0] = 't';
+	    buf->data[1] = 'S';
+	    buf->len_chars = 2;
+	    buf->len_bytes = 2;
+	    return RES_CHANGED;
+	  }
+	break;
+      }
+
+    /* Recover from a incorrect guess that it was a triplet. */
+    if (ch == '-') {
+      ctx->inword = false;
+    } else if (ctx->flag == CASE_UP) {
+      ch = irish_upcase(ch);
+    } else if (ctx->flag == CASE_CAPITALIZE) {
+      ch = irish_downcase(ch);
+    }
+
+    buf->data[0] = irish_upcase(ctx->special);
+    buf->data[1] = ch;
+    buf->len_chars = 2;
+    buf->len_bytes = 2;
+    ctx->special = SPECIAL_GA_UC;
+    return RES_CHANGED;
+  }
+
+  return RES_NOT_TOUCHED;
+}
+\f
 /* Save in BUF result of casing character CH.
 
    If not-NULL, NEXT points to the next character in the cased string.  If NULL,
@@ -543,6 +847,15 @@ case_characters (struct casing_str_buf *buf, struct casing_context *ctx,
   /* case SPECIAL_LT_DEL_DOT_ABOVE: */
   /* case SPECIAL_LT_INS_DOT_ABOVE: */
     ret = maybe_case_lithuanian (buf, ctx, flag, ch);
+    break;
+
+  case SPECIAL_GA_LC:
+  case SPECIAL_GA_UC:
+  case SPECIAL_GA_UC_NEXT:
+  case SPECIAL_GA_TRIPLET_B:
+  case SPECIAL_GA_TRIPLET_N:
+  case SPECIAL_GA_TRIPLET_T:
+    ret = maybe_case_irish (buf, ctx, flag, ch, next);
   }
 
   if (ret == RES_NOT_TOUCHED)
diff --git a/test/src/casefiddle-resources/irish-lowercase-1-ref.txt b/test/src/casefiddle-resources/irish-lowercase-1-ref.txt
new file mode 100644
index 00000000000..cbe9f601e9c
--- /dev/null
+++ b/test/src/casefiddle-resources/irish-lowercase-1-ref.txt
@@ -0,0 +1,211 @@
+ár n-acmhainní uisce
+ár n-acmhainní uisce
+ár n-acmhainní uisce
+ár n-acmhainní uisce
+ár n-acmhainní uisce
+ár nathair
+ár nathair
+ár nathair
+n-a shaighdiúir
+gan dul as aca ach le n-a chabhair
+eolaíocht na n-ábhar
+eolaíocht na n-ábhar
+eolaíocht na n-ábhar
+eolaíocht na n-ábhar
+eolaíocht na n-ábhar
+amhrán náisiúnta
+amhrán náisiúnta
+amhrán náisiúnta
+lucht na n-ealaíon
+lucht na n-ealaíon
+lucht na n-ealaíon
+lucht na n-ealaíon
+lucht na n-ealaíon
+neart daoine
+neart daoine
+neart daoine
+ceol na n-éan
+ceol na n-éan
+ceol na n-éan
+ceol na n-éan
+ceol na n-éan
+sa néal
+sa néal
+sa néal
+ord na n-imeachtaí
+ord na n-imeachtaí
+ord na n-imeachtaí
+ord na n-imeachtaí
+ord na n-imeachtaí
+nathair nimhe
+nathair nimhe
+nathair nimhe
+lucht adhartha na n-íomhánna
+lucht adhartha na n-íomhánna
+lucht adhartha na n-íomhánna
+lucht adhartha na n-íomhánna
+lucht adhartha na n-íomhánna
+níos measa
+níos measa
+níos measa
+gnéithe dár n-oidhreacht
+gnéithe dár n-oidhreacht
+gnéithe dár n-oidhreacht
+gnéithe dár n-oidhreacht
+gnéithe dár n-oidhreacht
+duine nochta
+duine nochta
+duine nochta
+cultúr na n-óg
+cultúr na n-óg
+cultúr na n-óg
+cultúr na n-óg
+cultúr na n-óg
+dhá nóiméad
+dhá nóiméad
+dhá nóiméad
+ocht n-uaire sa lá
+ocht n-uaire sa lá
+ocht n-uaire sa lá
+ocht n-uaire sa lá
+ocht n-uaire sa lá
+gúna nua
+gúna nua
+gúna nua
+formhór na n-údarás
+formhór na n-údarás
+formhór na n-údarás
+formhór na n-údarás
+formhór na n-údarás
+imoibreoir núicléach
+imoibreoir núicléach
+imoibreoir núicléach
+sean-airteagal
+seanairteagal
+bunioncaim
+bun-ioncaim
+buanorduithe
+buan-orduithe
+ár n-athair
+ár n-athair
+clár na n-ábhar
+clár na n-ábhar
+ceol na ndaoine
+ceol na ndaoine
+táim i ngrá leat
+táim i ngrá leat
+cén t-am é?
+cén t-am é?
+cén t-am é?
+cén t-am é?
+cén t-am é?
+tar ar ais!
+tar ar ais!
+tá an t-ádh orm inniu!
+tá an t-ádh orm inniu!
+tá an t-ádh orm inniu!
+tá an t-ádh orm inniu!
+tá an t-ádh orm inniu!
+rud tábhachtach
+rud tábhachtach
+rud tábhachtach
+den obair an t-eolas
+den obair an t-eolas
+den obair an t-eolas
+den obair an t-eolas
+den obair an t-eolas
+an t-éileamh a íoc
+an t-éileamh a íoc
+an t-éileamh a íoc
+an t-éileamh a íoc
+an t-éileamh a íoc
+an t-inneall cuardaigh is fearr
+an t-inneall cuardaigh is fearr
+an t-inneall cuardaigh is fearr
+an t-inneall cuardaigh is fearr
+an t-inneall cuardaigh is fearr
+an t-íochtar a chur in uachtar
+an t-íochtar a chur in uachtar
+an t-íochtar a chur in uachtar
+an t-íochtar a chur in uachtar
+an t-íochtar a chur in uachtar
+tabhair an t-ordú seo dó!
+tabhair an t-ordú seo dó!
+tabhair an t-ordú seo dó!
+tabhair an t-ordú seo dó!
+tabhair an t-ordú seo dó!
+tá an t-ór buí aige.
+tá an t-ór buí aige.
+tá an t-ór buí aige.
+tá an t-ór buí aige.
+tá an t-ór buí aige.
+an t-uisce beatha ar an tábla.
+an t-uisce beatha ar an tábla.
+an t-uisce beatha ar an tábla.
+an t-uisce beatha ar an tábla.
+an t-uisce beatha ar an tábla.
+an t-úrscéal is deireanaí
+an t-úrscéal is deireanaí
+an t-úrscéal is deireanaí
+an t-úrscéal is deireanaí
+an t-úrscéal is deireanaí
+dréacht-acht
+dréachtphlean
+dréacht-phlean
+dréacht-íocaíocht
+áitainmneacha
+áit-ainmneacha
+státurraithe
+stát-urraithe
+ar aon tslí
+ar aon tslí
+amach ón tsnáthaid
+amach ón tsnáthaid
+ar an tsráid
+ar an tsráid
+caint an tsráidbhaile
+caint an tsráidbhaile
+cora crua an tsaoil
+cora crua an tsaoil
+bholadh an tsáile
+bholadh an tsáile
+uair sa tseachtain
+uair sa tseachtain
+deireadh an tséasúir
+deireadh an tséasúir
+fear an tsiopa
+fear an tsiopa
+an tsíocháin a choimeád
+an tsíocháin a choimeád
+an tsochaí faisnéise
+an tsochaí faisnéise
+gaoth an tsóláis
+gaoth an tsóláis
+is beag an tsuim iad
+is beag an tsuim iad
+infheicthe ag an tsúil
+infheicthe ag an tsúil
+scríobhfaidh
+scríobhfaidh
+preabphas
+preabphas
+úsáidtear
+úsáidtear
+snagcheol
+snagcheol
+in-athnuaite agatsa
+in-athnuaite agatsa
+teanga dhomhanda
+teanga dhomhanda
+réaltsruth
+réaltsruth
+na hataí
+na hataí
+t-léine
+t-léine
+t-léine
+t-léine
+torc allta
+torc allta
+tsk tsk tsk a chara
+tsk tsk tsk a chara
diff --git a/test/src/casefiddle-resources/irish-lowercase-1.txt b/test/src/casefiddle-resources/irish-lowercase-1.txt
new file mode 100644
index 00000000000..dcb3454b96d
--- /dev/null
+++ b/test/src/casefiddle-resources/irish-lowercase-1.txt
@@ -0,0 +1,211 @@
+ÁR nACMHAINNÍ UISCE
+ÁR N-ACMHAINNÍ UISCE
+Ár nAcmhainní Uisce
+Ár n-Acmhainní Uisce
+ár n-acmhainní uisce
+Ár nathair
+ÁR NATHAIR
+Ár Nathair
+N-a shaighdiúir
+gan dul as aca ach le nA chabhair
+EOLAÍOCHT NA nÁBHAR
+EOLAÍOCHT NA n-ÁBHAR
+Eolaíocht na nÁbhar
+Eolaíocht na n-Ábhar
+eolaíocht na n-ábhar
+Amhrán náisiúnta
+Amhrán Náisiúnta
+AMHRÁN NÁISIÚNTA
+LUCHT NA nEALAÍON
+LUCHT NA n-EALAÍON
+Lucht na nEalaíon
+Lucht na n-Ealaíon
+lucht na n-ealaíon
+Neart Daoine
+neart daoine
+NEART DAOINE
+CEOL NA nÉAN
+CEOL NA n-ÉAN
+Ceol na nÉan
+Ceol na n-Éan
+ceol na n-éan
+Sa Néal
+Sa néal
+SA NÉAL
+ORD NA nIMEACHTAÍ
+ORD NA n-IMEACHTAÍ
+Ord na nImeachtaí
+Ord na n-Imeachtaí
+ord na n-imeachtaí
+Nathair Nimhe
+Nathair nimhe
+NATHAIR NIMHE
+LUCHT ADHARTHA NA nÍOMHÁNNA
+LUCHT ADHARTHA NA n-ÍOMHÁNNA
+Lucht Adhartha na nÍomhánna
+Lucht Adhartha na n-Íomhánna
+lucht adhartha na n-íomhánna
+Níos Measa
+níos measa
+NÍOS MEASA
+GNÉITHE DÁR nOIDHREACHT
+GNÉITHE DÁR n-OIDHREACHT
+Gnéithe Dár nOidhreacht
+Gnéithe Dár n-Oidhreacht
+gnéithe dár n-oidhreacht
+Duine Nochta
+Duine nochta
+DUINE NOCHTA
+CULTÚR NA nÓG
+CULTÚR NA n-ÓG
+Cultúr na nÓg
+Cultúr na n-Óg
+cultúr na n-óg
+Dhá Nóiméad
+Dhá nóiméad
+DHÁ NÓIMÉAD
+OCHT nUAIRE SA LÁ
+OCHT n-UAIRE SA LÁ
+Ocht nUaire Sa Lá
+Ocht n-Uaire Sa Lá
+ocht n-uaire sa lá
+Gúna Nua
+gúna nua
+GÚNA NUA
+FORMHÓR NA nÚDARÁS
+FORMHÓR NA n-ÚDARÁS
+Formhór na nÚdarás
+Formhór na n-Údarás
+formhór na n-údarás
+Imoibreoir Núicléach
+Imoibreoir núicléach
+IMOIBREOIR NÚICLÉACH
+sean-Airteagal
+SeanAirteagal
+BunIoncaim
+Bun-Ioncaim
+BuanOrduithe
+Buan-Orduithe
+ÁR nATHAIR
+Ár nAthair
+CLÁR NA nÁBHAR
+Clár na nÁbhar
+CEOL NA nDAOINE
+Ceol na nDaoine
+TÁIM I nGRÁ LEAT
+Táim i nGrá Leat
+CÉN tAM É?
+CÉN t-AM É?
+Cén tAm É?
+Cén t-Am É?
+cén t-am é?
+Tar Ar Ais!
+tar ar ais!
+TÁ AN tÁDH ORM INNIU!
+TÁ AN t-ÁDH ORM INNIU!
+Tá An tÁdh Orm Inniu!
+Tá An t-Ádh Orm Inniu!
+tá an t-ádh orm inniu!
+Rud Tábhachtach
+Rud tábhachtach
+rud tábhachtach
+DEN OBAIR AN tEOLAS
+DEN OBAIR AN t-EOLAS
+Den Obair an tEolas
+Den Obair an t-Eolas
+den obair an t-eolas
+AN tÉILEAMH A ÍOC
+AN t-ÉILEAMH A ÍOC
+An tÉileamh a Íoc
+An t-Éileamh a Íoc
+an t-éileamh a íoc
+AN tINNEALL CUARDAIGH IS FEARR
+AN t-INNEALL CUARDAIGH IS FEARR
+An tInneall Cuardaigh Is Fearr
+An t-Inneall Cuardaigh Is Fearr
+an t-inneall cuardaigh is fearr
+AN tÍOCHTAR A CHUR IN UACHTAR
+AN t-ÍOCHTAR A CHUR IN UACHTAR
+An tÍochtar a Chur In Uachtar
+An t-Íochtar a Chur In Uachtar
+an t-íochtar a chur in uachtar
+TABHAIR AN tORDÚ SEO DÓ!
+TABHAIR AN t-ORDÚ SEO DÓ!
+Tabhair An tOrdú Seo Dó!
+Tabhair An t-Ordú Seo Dó!
+tabhair an t-ordú seo dó!
+TÁ AN tÓR BUÍ AIGE.
+TÁ AN t-ÓR BUÍ AIGE.
+Tá An tÓr Buí Aige.
+Tá An t-Ór Buí Aige.
+tá an t-ór buí aige.
+AN tUISCE BEATHA AR AN TÁBLA.
+AN t-UISCE BEATHA AR AN TÁBLA.
+An tUisce Beatha Ar An Tábla.
+An t-Uisce Beatha Ar An Tábla.
+an t-uisce beatha ar an tábla.
+AN tÚRSCÉAL IS DEIREANAÍ
+AN t-ÚRSCÉAL IS DEIREANAÍ
+An tÚrscéal Is Deireanaí
+An t-Úrscéal Is Deireanaí
+an t-úrscéal is deireanaí
+Dréacht-Acht
+DréachtPhlean
+Dréacht-Phlean
+Dréacht-Íocaíocht
+ÁitAinmneacha
+Áit-Ainmneacha
+StátUrraithe
+Stát-Urraithe
+AR AON tSLÍ
+Ar Aon tSlí
+AMACH ÓN tSNÁTHAID
+Amach Ón tSnáthaid
+AR AN tSRÁID
+Ar An tSráid
+CAINT AN tSRÁIDBHAILE
+Caint An tSráidbhaile
+CORA CRUA AN tSAOIL
+Cora Crua An tSaoil
+BHOLADH AN tSÁILE
+Bholadh An tSáile
+UAIR SA tSEACHTAIN
+Uair Sa tSeachtain
+DEIREADH AN tSÉASÚIR
+Deireadh An tSéasúir
+FEAR AN tSIOPA
+Fear an tSiopa
+AN tSÍOCHÁIN A CHOIMEÁD
+An tSíocháin a Choimeád
+AN tSOCHAÍ FAISNÉISE
+An tSochaí Faisnéise
+GAOTH AN tSÓLÁIS
+Gaoth aN tSóláis
+IS BEAG AN tSUIM IAD
+Is Beag An tSuim Iad
+INFHEICTHE AG AN tSÚIL
+Infheicthe Ag An tSúil
+SCRÍOBHFAIDH
+Scríobhfaidh
+PREABPHAS
+Preabphas
+ÚSÁIDTEAR
+Úsáidtear
+SNAGCHEOL
+Snagcheol
+IN-ATHNUAITE AGATSA
+In-Athnuaite AGATSA
+TEANGA DHOMHANDA
+Teanga Dhomhanda
+RÉALTSRUTH
+Réaltsruth
+NA HATAÍ
+Na Hataí
+T-LÉINE
+T-Léine
+t-Léine
+t-léine
+TORC ALLTA
+Torc Allta
+TSK TSK TSK A CHARA
+Tsk Tsk Tsk a Chara
diff --git a/test/src/casefiddle-resources/irish-uppercase-1-ref.txt b/test/src/casefiddle-resources/irish-uppercase-1-ref.txt
new file mode 100644
index 00000000000..21d3e4a6126
--- /dev/null
+++ b/test/src/casefiddle-resources/irish-uppercase-1-ref.txt
@@ -0,0 +1,105 @@
+ORD NA bhFOCAL
+COSÁN NA bhFILÍ
+ÁR bPOBAL
+NÓRA NA bPORTACH
+I dTOSACH BÁIRE
+AN GHAEILGE I dTUAISCEART NA hÉIREANN
+AS AN gCEANTAR SIN
+I gCONTAE NA MÍ AGUS I gCONAMARA
+DÉ hAOINE
+OIRTHEAR NA hÁISE
+PARLAIMINT NA hEORPA
+POBLACHT NA hÉIREANN
+EALAÍN NA hIODÁILE
+NA hÍOSÁNAIGH
+ACADAMH NA hOLLSCOLAÍOCHTA
+TÍR NA hÓIGE
+TOGHCHÁN NA hUACHTARÁNACHTA
+NA hÚDARÁIS CHÁNACH
+I mBUN MO MHACHNAMH
+I mBÉAL FEIRSTE AGUS I mBAILE ÁTHA CLIATH
+ÁR nACMHAINNÍ UISCE
+EOLAÍOCHT NA nÁBHAR
+LUCHT NA nEALAÍON
+CEOL NA nÉAN
+ORD NA nIMEACHTAÍ
+LUCHT ADHARTHA NA nÍOMHÁNNA
+GNÉITHE DÁR nOIDHREACHT
+CULTÚR NA nÓG
+OCHT nUAIRE SA LÁ
+FORMHÓR NA nÚDARÁS
+ÁR nATHAIR
+CLÁR NA nÁBHAR
+LOCH nEATHACH
+CUMANN NA nÉIREANNACH AONTAITHE
+GRÉASÁN NA nIONTAS
+NÓIBHÍSEACHT NA nÍOSÁNACH
+I gCEANTAR NA nOILEÁN
+TÍR NA nÓG
+BAILE NA nULTACH
+GORT NA nÚLL
+CEOL NA nDAOINE
+I nDÚN NA nGALL
+TÁIM I nGRÁ LEAT
+LABHAIR SÉ I nGAEILGE!
+CÉN tAM É?
+TÁ AN tÁDH ORM INNIU!
+DEN OBAIR AN tEOLAS
+AN tÉILEAMH A ÍOC
+AN tINNEALL CUARDAIGH IS FEARR
+AN tÍOCHTAR A CHUR IN UACHTAR
+TABHAIR AN tORDÚ SEO DÓ!
+TÁ AN tÓR BUÍ AIGE.
+AN tUISCE BEATHA AR AN TÁBLA.
+AN tÚRSCÉAL IS DEIREANAÍ
+AN tACHT OIDEACHAIS
+AN tÁIVÉ MÁIRIA
+AN tEARRACH ARABACH
+AN tÉIRÍ AMACH
+AN tIMEALL
+AN tÍOSÁNACH PEADAR CANISIUS
+AN tOILEÁNACH
+AN tÓR MUIRE
+AN tUASAL ÉAMON Ó CUÍV
+AN tÚDARÁS UM BÓITHRE NÁISIÚNTA
+AR AON tSLÍ
+BÉAL ÁTHA AN tSLÉIBHE
+AMACH ÓN tSNÁTHAID
+BANRÍON AN tSNEACHTA
+AR AN tSRÁID
+CAINT AN tSRÁIDBHAILE
+CORA CRUA AN tSAOIL
+BHOLADH AN tSÁILE
+UAIR SA tSEACHTAIN
+DEIREADH AN tSÉASÚIR
+FEAR AN tSIOPA
+AN tSÍOCHÁIN A CHOIMEÁD
+AN tSOCHAÍ FAISNÉISE
+GAOTH AN tSÓLÁIS
+IS BEAG AN tSUIM IAD
+INFHEICTHE AG AN tSÚIL
+CNOC AN tSAMHRAIDH
+CIONN tSÁILE
+AN tSEIRBHÍS PHOIBLÍ
+BAILE AN tSÉIPÉIL
+AN tSIRIA
+AN tSÍN
+OIFIG AN tSOLÁTHAIR
+POLL AN tSÓMAIS
+EOLAIRE AN tSUÍMH
+CASADH AN tSÚGÁIN
+SCRÍOBHFAIDH
+PREABPHAS
+ÚSÁIDTEAR
+SNAGCHEOL
+STÁITSE IMBOLC
+IN-ATHNUAITE AGATSA
+TEANGA DHOMHANDA
+RÉALTSRUTH
+NA HATAÍ
+NA HATAÍ
+ÁR NATHAIR
+ÁR NATHAIR
+T-LÉINE
+TORC ALLTA
+TSK TSK TSK A CHARA
diff --git a/test/src/casefiddle-resources/irish-uppercase-1.txt b/test/src/casefiddle-resources/irish-uppercase-1.txt
new file mode 100644
index 00000000000..b95e0aa04df
--- /dev/null
+++ b/test/src/casefiddle-resources/irish-uppercase-1.txt
@@ -0,0 +1,105 @@
+ord na bhfocal
+Cosán na bhFilí
+ár bpobal
+Nóra na bPortach
+i dtosach báire
+An Ghaeilge i dTuaisceart na hÉireann
+as an gceantar sin
+I gContae na Mí agus i gConamara
+Dé hAoine
+Oirthear na hÁise
+Parlaimint na hEorpa
+Poblacht na hÉireann
+Ealaín na hIodáile
+na hÍosánaigh
+Acadamh na hOllscolaíochta
+Tír na hÓige
+toghchán na hUachtaránachta
+na hÚdaráis Chánach
+I mbun mo mhachnamh
+I mBéal Feirste agus i mBaile Átha Cliath
+ár n-acmhainní uisce
+eolaíocht na n-ábhar
+lucht na n-ealaíon
+ceol na n-éan
+ord na n-imeachtaí
+lucht adhartha na n-íomhánna
+gnéithe dár n-oidhreacht
+cultúr na n-óg
+ocht n-uaire sa lá
+formhór na n-údarás
+Ár nAthair
+Clár na nÁbhar
+Loch nEathach
+Cumann na nÉireannach Aontaithe
+Gréasán na nIontas
+nóibhíseacht na nÍosánach
+i gCeantar na nOileán
+Tír na nÓg
+Baile na nUltach
+Gort na nÚll
+ceol na ndaoine
+i nDún na nGall
+táim i ngrá leat
+labhair sé i nGaeilge!
+cén t-am é?
+tá an t-ádh orm inniu!
+Den obair an t-eolas
+An t-éileamh a íoc
+an t-inneall cuardaigh is fearr
+an t-íochtar a chur in uachtar
+Tabhair an t-ordú seo dó!
+Tá an t-ór buí aige.
+an t-uisce beatha ar an tábla.
+an t-úrscéal is deireanaí
+An tAcht Oideachais
+an tÁivé Máiria
+An tEarrach Arabach
+An tÉirí Amach
+An tImeall
+An tÍosánach Peadar Canisius
+An tOileánach
+An tÓr Muire
+an tUasal Éamon Ó Cuív
+An tÚdarás um Bóithre Náisiúnta
+ar aon tslí
+Béal Átha an tSléibhe
+Amach ón tsnáthaid
+Banríon an tSneachta
+ar an tsráid
+Caint an tSráidbhaile
+cora crua an tsaoil
+bholadh an tsáile
+uair sa tseachtain
+deireadh an tséasúir
+fear an tsiopa
+an tsíocháin a choimeád
+an tsochaí faisnéise
+gaoth an tsóláis
+Is beag an tsuim iad
+infheicthe ag an tsúil
+Cnoc an tSamhraidh
+Cionn tSáile
+an tSeirbhís Phoiblí
+Baile an tSéipéil
+An tSiria
+An tSín
+Oifig an tSoláthair
+Poll an tSómais
+Eolaire an tSuímh
+Casadh an tSúgáin
+scríobhfaidh
+preabphas
+úsáidtear
+snagcheol
+Stáitse Imbolc
+in-athnuaite agatsa
+Teanga Dhomhanda
+Réaltsruth
+na hataí
+Na Hataí
+ár nathair
+Ár Nathair
+t-léine
+torc allta
+tsk tsk tsk a chara
diff --git a/test/src/casefiddle-tests.el b/test/src/casefiddle-tests.el
index f7b0da41029..e5309066c9c 100644
--- a/test/src/casefiddle-tests.el
+++ b/test/src/casefiddle-tests.el
@@ -22,6 +22,11 @@
 (require 'case-table)
 (require 'ert)
 
+(defvar casefiddle-tests--resources-dir
+  (concat (concat (file-name-directory (or load-file-name buffer-file-name))
+                  "/casefiddle-resources/"))
+  "Path to casefiddle-resources directory next to the \"casefiddle-tests.el\" file.")
+
 (ert-deftest casefiddle-tests-char-properties ()
   "Sanity check of character Unicode properties."
   (should-not
@@ -161,17 +166,18 @@ casefiddle-tests--test-casing
         (while (and func-pairs expected)
           (setq funcs (car func-pairs)
                 getters (list get-string get-region))
-          (while (and funcs getters)
-            (let ((got (funcall (car getters) (car funcs))))
-              (unless (string-equal got (car expected))
-                (let ((fmt (length (symbol-name (car funcs)))))
-                  (setq fmt (format "\n%%%ds: %%s" (max fmt 8)))
-                  (push (format (concat fmt fmt fmt)
-                                (car funcs) (funcall fmt-str input)
-                                "expected" (funcall fmt-str (car expected))
-                                "but got" (funcall fmt-str got))
-                        errors))))
-            (setq funcs (cdr funcs) getters (cdr getters)))
+          (when (car expected)
+            (while (and funcs getters)
+              (let ((got (funcall (car getters) (car funcs))))
+                (unless (string-equal got (car expected))
+                  (let ((fmt (length (symbol-name (car funcs)))))
+                    (setq fmt (format "\n%%%ds: %%s" (max fmt 8)))
+                    (push (format (concat fmt fmt fmt)
+                                  (car funcs) (funcall fmt-str input)
+                                  "expected" (funcall fmt-str (car expected))
+                                  "but got" (funcall fmt-str got))
+                          errors))))
+              (setq funcs (cdr funcs) getters (cdr getters))))
           (setq func-pairs (cdr func-pairs) expected (cdr expected))))
       errors)
     (cons () tests))))
@@ -268,6 +274,36 @@ casefiddle-tests--test-casing
         ("į\u0307"                ; i-ogonek + dot above
          "Į" "į\u0307" "Į" "Į" "lt"))))))
 
+
+(defun casefiddle--read-lines (test-file)
+  (with-temp-buffer
+    (insert-file-contents (concat casefiddle-tests--resources-dir test-file))
+    (split-string (buffer-string) "\n" nil " +")))
+
+(ert-deftest casefiddle-test-irish ()
+  (let (tests)
+    ;; Read upcase test cases
+    (let ((input    (casefiddle--read-lines "irish-uppercase-1.txt"))
+          (expected (casefiddle--read-lines "irish-uppercase-1-ref.txt")))
+      (while (and input expected)
+        (push (list (car input) (car expected) nil nil nil "ga") tests)
+        (setq input (cdr input) expected (cdr expected)))
+      (should-not (or input expected)))
+
+    ;; Read downcase test cases
+    (let ((input    (casefiddle--read-lines "irish-lowercase-1.txt"))
+          (expected (casefiddle--read-lines "irish-lowercase-1-ref.txt")))
+      (while (and input expected)
+        (let ((test (assoc (car input) tests)))
+          (if test
+              (setcar (cddr test) (car expected))
+            (push (list (car input) nil (car expected) nil nil "ga") tests)))
+        (setq input (cdr input) expected (cdr expected)))
+      (should-not (or input expected)))
+
+    (should-not (with-temp-buffer (casefiddle-tests--test-casing tests)))))
+
+
 (ert-deftest casefiddle-tests-casing-byte8 ()
   (should-not
    (with-temp-buffer
-- 
2.12.0.246.ga2ecc84866-goog