Prevent fish from crashing if non-essential terminfo strings not found

On systems where the terminfo for TERM does not contain a string for
attributes such as enter_underline_mode, etc. fish was crashing with a
fatal error message and a note to email the developers.

These are non-essential text attribute changes and should not trigger
such a failure.

src/builtin_set_color.cpp

@@ -193,36 +193,36 @@ int builtin_set_color(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     output_set_writer(set_color_builtin_outputter);
 
     if (bold && enter_bold_mode) {
-        writembs(tparm(enter_bold_mode));
+        writembs_nofail(tparm(enter_bold_mode));
     }
 
     if (underline && enter_underline_mode) {
-        writembs(enter_underline_mode);
+        writembs_nofail(enter_underline_mode);
     }
 
     if (italics && enter_italics_mode) {
-        writembs(enter_italics_mode);
+        writembs_nofail(enter_italics_mode);
     }
 
     if (dim && enter_dim_mode) {
-        writembs(enter_dim_mode);
+        writembs_nofail(enter_dim_mode);
     }
 
     if (reverse && enter_reverse_mode) {
-        writembs(enter_reverse_mode);
+        writembs_nofail(enter_reverse_mode);
     } else if (reverse && enter_standout_mode) {
-        writembs(enter_standout_mode);
+        writembs_nofail(enter_standout_mode);
     }
 
     if (bgcolor != NULL && bg.is_normal()) {
         write_color(rgb_color_t::black(), false /* not is_fg */);
-        writembs(tparm(exit_attribute_mode));
+        writembs_nofail(tparm(exit_attribute_mode));
     }
 
     if (!fg.is_none()) {
         if (fg.is_normal() || fg.is_reset()) {
             write_color(rgb_color_t::black(), true /* is_fg */);
-            writembs(tparm(exit_attribute_mode));
+            writembs_nofail(tparm(exit_attribute_mode));
         } else {
             if (!write_color(fg, true /* is_fg */)) {
                 // We need to do *something* or the lack of any output messes up

src/output.cpp

@@ -274,7 +274,7 @@ void set_color(rgb_color_t c, rgb_color_t c2) {
         if (bg_set && !last_bg_set) {
             // Background color changed and is set, so we enter bold mode to make reading easier.
             // This means bold mode is _always_ on when the background color is set.
-            writembs(enter_bold_mode);
+            writembs_nofail(enter_bold_mode);
         }
         if (!bg_set && last_bg_set) {
             // Background color changed and is no longer set, so we exit bold mode.
@@ -332,41 +332,41 @@ void set_color(rgb_color_t c, rgb_color_t c2) {
 
     // Lastly, we set bold, underline, italics, dim, and reverse modes correctly.
     if (is_bold && !was_bold && enter_bold_mode && strlen(enter_bold_mode) > 0 && !bg_set) {
-        writembs(tparm(enter_bold_mode));
+        writembs_nofail(tparm(enter_bold_mode));
         was_bold = is_bold;
     }
 
     if (was_underline && !is_underline) {
-        writembs(exit_underline_mode);
+        writembs_nofail(exit_underline_mode);
     }
 
     if (!was_underline && is_underline) {
-        writembs(enter_underline_mode);
+        writembs_nofail(enter_underline_mode);
     }
     was_underline = is_underline;
 
     if (was_italics && !is_italics && enter_italics_mode && strlen(enter_italics_mode) > 0) {
-        writembs(exit_italics_mode);
+        writembs_nofail(exit_italics_mode);
         was_italics = is_italics;
     }
 
     if (!was_italics && is_italics && enter_italics_mode && strlen(enter_italics_mode) > 0) {
-        writembs(enter_italics_mode);
+        writembs_nofail(enter_italics_mode);
         was_italics = is_italics;
     }
 
     if (is_dim && !was_dim && enter_dim_mode && strlen(enter_dim_mode) > 0) {
-        writembs(enter_dim_mode);
+        writembs_nofail(enter_dim_mode);
         was_dim = is_dim;
     }
 
     if (is_reverse && !was_reverse) {
         // Some terms do not have a reverse mode set, so standout mode is a fallback.
         if (enter_reverse_mode && strlen(enter_reverse_mode) > 0) {
-            writembs(enter_reverse_mode);
+            writembs_nofail(enter_reverse_mode);
             was_reverse = is_reverse;
         } else if (enter_standout_mode && strlen(enter_standout_mode) > 0) {
-            writembs(enter_standout_mode);
+            writembs_nofail(enter_standout_mode);
             was_reverse = is_reverse;
         }
     }
@@ -550,10 +550,10 @@ rgb_color_t parse_color(const env_var_t &var, bool is_background) {
 }
 
 /// Write specified multibyte string.
-void writembs_check(char *mbs, const char *mbs_name, const char *file, long line) {
+void writembs_check(char *mbs, const char *mbs_name, bool critical, const char *file, long line) {
     if (mbs != NULL) {
         tputs(mbs, 1, &writeb);
-    } else {
+    } else if (critical) {
         auto term = env_get(L"TERM");
         const wchar_t *fmt =
             _(L"Tried to use terminfo string %s on line %ld of %s, which is "

src/output.h

@@ -30,8 +30,9 @@ enum {
 
 void set_color(rgb_color_t c, rgb_color_t c2);
 
-void writembs_check(char *mbs, const char *mbs_name, const char *file, long line);
+void writembs_check(char *mbs, const char *mbs_name, bool critical, const char *file, long line);
-#define writembs(mbs) writembs_check((mbs), #mbs, __FILE__, __LINE__)
+#define writembs(mbs) writembs_check((mbs), #mbs, true, __FILE__, __LINE__)
+#define writembs_nofail(mbs) writembs_check((mbs), #mbs, false, __FILE__, __LINE__)
 
 int writech(wint_t ch);