PATCH: support for italic and faint fonts from region_highlight

[Oliver Kiddle <opk@xxxxxxx>]

Having got rid of the OFF flags in zattr, there are bits available for
additional attributes. This patch adds support for italic and faint in
$region_highlight using two of the available 8 bits.

Other attributes with widely documented sequences include blink,
strikeout, double underline, invisible. None of these strike me as
especially useful and adding them might limit future expansion. I've
also come across fast blinking, overline, borders, rounded borders,
curly, dotted, dashed and coloured underline.

One approach could be to find a way to support user-defined attributes
e.g:

  zle_highlight+=(
    'user1_begin_code:\e[9m' 'user1_end_code:\e[29m'
    'user2_begin_code:\e[58;5;88m\e[4;3m' 'user2_end_code:\e[4;0m'
    'user2_excl:underline'
    special:user1 paste:user2
  )

This patch doesn't address prompts at all. We've discussed ideas before
such as %O...%o. or %A{italic}. The %A form would need to support
ways to unset attributes too so "noitalic" and perhaps "normal" for font
weight that is neither bold nor faint. But would it be better to instead
use an associative array and lookup attributes via that, e.g:

  zle_theme=( [warning]='fg=yellow' )
  print -P '%A{warning}Yellow text%a'

I currently need to convert colours to a variety of forms in my .zshrc
to suit a variety of commands and this could be made easier.

A final matter where ideas and opinions would be useful is the
precedence of values in region_highlight. In my own setup I've
experienced frustrations with array order not being a convenient way
to manage this and looking at external plugins, everyone just appends
values so I doubt it works especially well when mixing plugins.

Most attributes are merged so if one value requires bold and
another underline, you get both. But for colours, entries later in
region_highlight take precedence. I've followed that pattern for font
weight. A special-case appears to have been made for special character
highlighting. In one instance, I suspect a bug in the old code. A
solution that comes to mind would be to allow a layer= entry in the
attribute list. We could assign default layers to region, paste, special
etc. This also might not need users to wait for plugin authors to update
their plugin where plugins allow attributes to be customised. What would
be a good naming/numbering scheme for layers, are there established
existing conventions on that, e.g. in the graphics field? Would we also
need another parameter to mask what is passed through from lower layers?

Finally, some notes on the patch: italic does have a termcap entry but
it is sometimes missing where it would be supported so this falls back
on defaults. Does anyone have a view on whether we should use "italics"
instead of "italic" as the naming? There is no termcap entry for faint
so that is hard-coded. To avoid duplicating all of tsetcap() I've
extended it to handle fake termcap entries for higher-numbered values of
the cap parameter and an added X in the macro name, e.g. TCXFAINTBEG.

Oliver

diff --git a/Doc/Zsh/zle.yo b/Doc/Zsh/zle.yo
index 58700072a..60254e828 100644
--- a/Doc/Zsh/zle.yo
+++ b/Doc/Zsh/zle.yo
@@ -2780,9 +2780,13 @@ This works similarly to the foreground colour, except the background is
 not usually affected by the bold attribute.
 )
 item(tt(bold))(
-The characters in the given context are shown in a bold font.
+The characters in the given context are shown with a bold font weight.
 Not all terminals distinguish bold fonts.
 )
+item(tt(faint))(
+The characters in the given context are shown with a faint font weight.
+Not all terminals distinguish faint fonts.
+)
 item(tt(standout))(
 The characters in the given context are shown in the terminal's standout
 mode.  The actual effect is specific to the terminal; on many terminals it
@@ -2796,6 +2800,10 @@ The characters in the given context are shown underlined.  Some
 terminals show the foreground in a different colour instead; in this
 case whitespace will not be highlighted.
 )
+item(tt(italic))(
+The characters in the given context are shown in a italic font.
+Not all terminals support italic fonts.
+)
 enditem()
 
 The characters described above as `special' are as follows.  The
diff --git a/Src/Zle/zle_refresh.c b/Src/Zle/zle_refresh.c
index d56478147..e2131fb05 100644
--- a/Src/Zle/zle_refresh.c
+++ b/Src/Zle/zle_refresh.c
@@ -1193,23 +1193,23 @@ zrefresh(void)
 		offset = predisplaylen; /* increment over it */
 	    if (rhp->start + offset <= tmppos &&
 		tmppos < rhp->end + offset) {
-		if (rhp->atr & (TXTFGCOLOUR|TXTBGCOLOUR)) {
-		    /* override colour with later entry */
-		    base_attr = rhp->atr;
-		} else {
-		    /* no colour set yet */
-		    base_attr |= rhp->atr;
-		}
+		/* override colour with later entry */
+		if (rhp->atr & (TXTFGCOLOUR|TXTBGCOLOUR))
+		    base_attr &= ~TXT_ATTR_COLOUR_MASK;
+		/* override font weight with later entry */
+		if (rhp->atr & TXT_ATTR_FONT_WEIGHT)
+		    base_attr &= ~TXT_ATTR_FONT_WEIGHT;
+		base_attr |= rhp->atr;
 	    }
 	}
-	if (special_attr & (TXTFGCOLOUR|TXTBGCOLOUR)) {
-	    /* keep colours from special attributes */
-	    all_attr = special_attr |
-		(base_attr & ~TXT_ATTR_COLOUR_MASK);
-	} else {
-	    /* keep colours from standard attributes */
-	    all_attr = special_attr | base_attr;
-	}
+	all_attr = base_attr;
+	/* keep colours from special attributes */
+	if (special_attr & (TXTFGCOLOUR|TXTBGCOLOUR))
+	    all_attr &= ~TXT_ATTR_COLOUR_MASK;
+	/* keep font weight from special attributes */
+	if (special_attr & TXT_ATTR_FONT_WEIGHT)
+	    all_attr &= ~TXT_ATTR_FONT_WEIGHT;
+	all_attr |= special_attr;
 
 	if (t == scs)			/* if cursor is here, remember it */
 	    rpms.nvcs = rpms.s - nbuf[rpms.nvln = rpms.ln];
@@ -2441,14 +2441,14 @@ singlerefresh(ZLE_STRING_T tmpline, int tmpll, int tmpcs)
 		}
 	    }
 	}
-	if (special_attr & (TXTFGCOLOUR|TXTBGCOLOUR)) {
-	    /* keep colours from special attributes */
-	    all_attr = special_attr |
-		(base_attr & ~TXT_ATTR_COLOUR_MASK);
-	} else {
-	    /* keep colours from standard attributes */
-	    all_attr = special_attr | base_attr;
-	}
+	all_attr = base_attr;
+	/* keep colours from special attributes */
+	if (special_attr & (TXTFGCOLOUR|TXTBGCOLOUR))
+	    all_attr &= ~TXT_ATTR_COLOUR_MASK;
+	/* keep font weight from special attributes */
+	if (special_attr & TXT_ATTR_FONT_WEIGHT)
+	    all_attr &= ~TXT_ATTR_FONT_WEIGHT;
+	all_attr |= special_attr;
 
 	if (tmpline[t0] == ZWC('\t')) {
 	    for (*vp++ = zr_sp; (vp - vbuf) & 7; )
diff --git a/Src/init.c b/Src/init.c
index 75ef2e094..9eef3f16d 100644
--- a/Src/init.c
+++ b/Src/init.c
@@ -747,7 +747,7 @@ init_shout(void)
 static char *tccapnams[TC_COUNT] = {
     "cl", "le", "LE", "nd", "RI", "up", "UP", "do",
     "DO", "dc", "DC", "ic", "IC", "cd", "ce", "al", "dl", "ta",
-    "md", "so", "us", "me", "se", "ue", "ch",
+    "md", "so", "us", "ZH", "me", "se", "ue", "ZR", "ch",
     "ku", "kd", "kl", "kr", "sc", "rc", "bc", "AF", "AB"
 };
 
@@ -872,6 +872,19 @@ init_term(void)
 	/* The following is an attempt at a heuristic,
 	 * but it fails in some cases */
 	/* rprompt_indent = ((hasam && !hasbw) || hasye || !tccan(TCLEFT)); */
+
+	/* if there's no termcap entry for italics, use CSI 3 m */
+	if (!tccan(TCITALICSBEG)) {
+	    zsfree(tcstr[TCITALICSBEG]);
+	    tcstr[TCITALICSBEG] = ztrdup("\033[3m");
+	    tclen[TCITALICSBEG] = 4;
+	}
+	if (!tccan(TCITALICSEND)) {
+	    zsfree(tcstr[TCITALICSEND]);
+	    tcstr[TCITALICSEND] = ztrdup("\033[23m");
+	    tclen[TCITALICSEND] = 5;
+	}
+
     }
     return 1;
 }
diff --git a/Src/prompt.c b/Src/prompt.c
index 880194f87..dc575085f 100644
--- a/Src/prompt.c
+++ b/Src/prompt.c
@@ -45,6 +45,12 @@ mod_export zattr txtpendingattrs;
 /**/
 mod_export zattr txtunknownattrs;
 
+/* common escape sequences not found in termcap */
+
+static char *tcxstr[TCX_COUNT - TC_COUNT] = {
+    "\e[2m", /* faint */
+};
+
 /* the command stack for use with %_ in prompts */
 
 /**/
@@ -1004,22 +1010,23 @@ stradd(char *d)
 mod_export void
 tsetcap(int cap, int flags)
 {
-    if (tccan(cap) && !isset(SINGLELINEZLE) &&
+    if ((cap >= TC_COUNT || tccan(cap)) && !isset(SINGLELINEZLE) &&
         !(termflags & (TERM_NOUP|TERM_BAD|TERM_UNKNOWN))) {
+	const char *tcseq = (cap >= TC_COUNT) ? tcxstr[cap - TC_COUNT] : tcstr[cap];
 	switch (flags) {
 	case TSC_RAW:
-	    tputs(tcstr[cap], 1, putraw);
+	    tputs(tcseq, 1, putraw);
 	    break;
 	case 0:
 	default:
-	    tputs(tcstr[cap], 1, putshout);
+	    tputs(tcseq, 1, putshout);
 	    break;
 	case TSC_PROMPT:
 	    if (!bv->dontcount) {
 		addbufspc(1);
 		*bv->bp++ = Inpar;
 	    }
-	    tputs(tcstr[cap], 1, putstr);
+	    tputs(tcseq, 1, putstr);
 	    if (!bv->dontcount) {
 		int glitch = 0;
 
@@ -1590,7 +1597,14 @@ applytextattributes(int flags)
 	    turnoff &= turnoff - 1;
     }
 
-    if (keepcount < turncount || (change & ~txtpendingattrs & TXTBOLDFACE)) {
+    /* enabling bold can be relied upon to disable faint */
+    if (txtcurrentattrs & TXTFAINT && txtpendingattrs & TXTBOLDFACE) {
+	--turncount;
+	change &= ~TXTFAINT;
+    }
+
+    if (keepcount < turncount ||
+	    (change & ~txtpendingattrs & TXT_ATTR_FONT_WEIGHT)) {
 	tsetcap(TCALLATTRSOFF, flags);
 	/* this cleared all attributes, may need to restore some */
 	change = txtpendingattrs & TXT_ATTR_ALL & ~txtunknownattrs;
@@ -1607,13 +1621,19 @@ applytextattributes(int flags)
 	    /* in some cases, that clears all attributes */
 	    change = txtpendingattrs & TXT_ATTR_ALL & ~txtunknownattrs;
 	}
+	if (change & ~txtpendingattrs & TXTITALIC)
+	    tsetcap(TCITALICSEND, flags);
     }
     if (change & txtpendingattrs & TXTBOLDFACE)
 	tsetcap(TCBOLDFACEBEG, flags);
+    if (change & txtpendingattrs & TXTFAINT)
+	tsetcap(TCXFAINTBEG, flags);
     if (change & txtpendingattrs & TXTSTANDOUT)
 	tsetcap(TCSTANDOUTBEG, flags);
     if (change & txtpendingattrs & TXTUNDERLINE)
 	tsetcap(TCUNDERLINEBEG, flags);
+    if (change & txtpendingattrs & TXTITALIC)
+	tsetcap(TCITALICSBEG, flags);
 
     if (change & TXT_ATTR_FG_MASK)
 	set_colour_attribute(txtpendingattrs, COL_SEQ_FG, flags);
@@ -1700,9 +1720,11 @@ struct highlight {
 
 static const struct highlight highlights[] = {
     { "none", 0, TXT_ATTR_ALL },
-    { "bold", TXTBOLDFACE, 0 },
+    { "bold", TXTBOLDFACE, TXTFAINT },
+    { "faint", TXTFAINT, TXTBOLDFACE },
     { "standout", TXTSTANDOUT, 0 },
     { "underline", TXTUNDERLINE, 0 },
+    { "italic", TXTITALIC, 0 },
     { NULL, 0, 0 }
 };
 
diff --git a/Src/zsh.h b/Src/zsh.h
index 35ae033e3..e8b9fd84b 100644
--- a/Src/zsh.h
+++ b/Src/zsh.h
@@ -2648,20 +2648,26 @@ struct ttyinfo {
 #define TCBOLDFACEBEG  18
 #define TCSTANDOUTBEG  19
 #define TCUNDERLINEBEG 20
-#define TCALLATTRSOFF  21
-#define TCSTANDOUTEND  22
-#define TCUNDERLINEEND 23
-#define TCHORIZPOS     24
-#define TCUPCURSOR     25
-#define TCDOWNCURSOR   26
-#define TCLEFTCURSOR   27
-#define TCRIGHTCURSOR  28
-#define TCSAVECURSOR   29
-#define TCRESTRCURSOR  30
-#define TCBACKSPACE    31
-#define TCFGCOLOUR     32
-#define TCBGCOLOUR     33
-#define TC_COUNT       34
+#define TCITALICSBEG   21
+#define TCALLATTRSOFF  22
+#define TCSTANDOUTEND  23
+#define TCUNDERLINEEND 24
+#define TCITALICSEND   26
+#define TCHORIZPOS     26
+#define TCUPCURSOR     27
+#define TCDOWNCURSOR   28
+#define TCLEFTCURSOR   29
+#define TCRIGHTCURSOR  30
+#define TCSAVECURSOR   31
+#define TCRESTRCURSOR  32
+#define TCBACKSPACE    33
+#define TCFGCOLOUR     34
+#define TCBGCOLOUR     35
+#define TC_COUNT       36
+
+/* escape sequences for which there is no termcap sequence */
+#define TCXFAINTBEG    36
+#define TCX_COUNT      37
 
 #define tccan(X) (tclen[X])
 
@@ -2676,12 +2682,14 @@ struct ttyinfo {
 #endif
 
 #define TXTBOLDFACE   0x0001
-#define TXTSTANDOUT   0x0002
-#define TXTUNDERLINE  0x0004
-#define TXTFGCOLOUR   0x0008
-#define TXTBGCOLOUR   0x0010
+#define TXTFAINT      0x0002
+#define TXTSTANDOUT   0x0004
+#define TXTUNDERLINE  0x0008
+#define TXTITALIC     0x0010
+#define TXTFGCOLOUR   0x0020
+#define TXTBGCOLOUR   0x0040
 
-#define TXT_ATTR_ALL  0x001F
+#define TXT_ATTR_ALL  0x007F
 
 /*
  * Indicates to zle_refresh.c that the character entry is an
@@ -2690,7 +2698,10 @@ struct ttyinfo {
 #define TXT_MULTIWORD_MASK  0x0400
 
 /* used when, e.g an invalid colour is specified */
-#define TXT_ERROR 0xF00000F000000800
+#define TXT_ERROR 0xF00000F000000003
+
+/* Mask for font weight */
+#define TXT_ATTR_FONT_WEIGHT     (TXTBOLDFACE|TXTFAINT)
 
 /* Mask for colour to use in foreground */
 #define TXT_ATTR_FG_COL_MASK     0x000000FFFFFF0000