you do not get to win https://www.youtube.com/watch?v=ASacQYJWOPI

src/lib/input.c

@@ -633,6 +633,8 @@ typedef enum {
   STATE_TDA2, // tertiary DA, got '|', first hex nibble
   STATE_TDA3, // tertiary DA, second hex nibble
   STATE_SDA,  // secondary DA (CSI > Pp ; Pv ; Pc c)
+  STATE_SDA_VER,  // secondary DA, got semi, reading to next semi
+  STATE_SDA_DRAIN, // drain secondary DA to 'c'
   STATE_DA,   // primary DA   (CSI ? ... c) OR XTSMGRAPHICS OR DECRPM
   STATE_DA_1, // got '1', XTSMGRAPHICS color registers or primary DA
   STATE_DA_1_SEMI, // got '1;'
@@ -817,6 +819,32 @@ stash_string(query_state* inits){
   return 0;
 }
 
+// use the version extracted from Secondary Device Attributes, assuming that
+// it is Alacritty (we ought check the specified terminfo database entry).
+// Alacritty writes its crate version with each more significant portion
+// multiplied by 100^{portion ID}, where major, minor, patch are 2, 1, 0.
+// what happens when a component exceeds 99? who cares. support XTVERSION.
+static char*
+set_sda_version(query_state* inits){
+  int maj, min, patch;
+  if(inits->numeric <= 0){
+    return NULL;
+  }
+  maj = inits->numeric / 10000;
+  min = (inits->numeric % 10000) / 100;
+  patch = inits->numeric % 100;
+  if(maj >= 100 || min >= 100 || patch >= 100){
+    return NULL;
+  }
+  // 3x components (two digits max each), 2x '.', NUL would suggest 9 bytes,
+  // but older gcc __builtin___sprintf_chk insists on 13. fuck it. FIXME.
+  char* buf = malloc(13);
+  if(buf){
+    sprintf(buf, "%d.%d.%d", maj, min, patch);
+  }
+  return buf;
+}
+
 // FIXME ought implement the full Williams automaton
 // FIXME sloppy af in general
 // returns 1 after handling the Device Attributes response, 0 if more input
@@ -880,7 +908,15 @@ pump_control_read(query_state* inits, unsigned char c){
       if(c == '?'){
         inits->state = STATE_DA; // could also be DECRPM/XTSMGRAPHICS
       }else if(c == '>'){
-        inits->state = STATE_SDA;
+        // SDA yields up Alacritty's crate version, but it doesn't unambiguously
+        // identify Alacritty. If we've got any other version information, skip
+        // directly to STATE_SDA_DRAIN, rather than doing STATE_SDA_VER.
+        if(inits->qterm || inits->version){
+          loginfo("Identified terminal already; ignoring DA2\n");
+          inits->state = STATE_SDA_DRAIN;
+        }else{
+          inits->state = STATE_SDA;
+        }
       }else if(isdigit(c)){
         inits->numeric = 0;
         if(ruts_numeric(&inits->numeric, c)){
@@ -1018,11 +1054,31 @@ pump_control_read(query_state* inits, unsigned char c){
       }
       inits->state = STATE_TDA2;
       if(ruts_string(inits, STATE_TDA1)){
-        inits->state = STATE_DCS_DRAIN;
+        inits->state = STATE_DCS_DRAIN; // FIXME return -1?
       }
       inits->numeric = 0;
       break;
     case STATE_SDA:
+      if(c == ';'){
+        inits->state = STATE_SDA_VER;
+        inits->numeric = 0;
+      }else if(c == 'c'){
+        inits->state = STATE_NULL;
+      }
+      break;
+    case STATE_SDA_VER:
+      if(c == ';'){
+        inits->state = STATE_SDA_DRAIN;
+        loginfo("Got DA2 Pv: %u\n", inits->numeric);
+        // if a version was set, we couldn't have arrived here
+        if((inits->version = set_sda_version(inits)) == NULL){
+          return -1;
+        }
+      }else if(ruts_numeric(&inits->numeric, c)){
+        return -1;
+      }
+      break;
+    case STATE_SDA_DRAIN:
       if(c == 'c'){
         inits->state = STATE_NULL;
       }
@@ -1234,7 +1290,7 @@ int ncinputlayer_init(tinfo* tcache, FILE* infp, queried_terminals_e* detected,
     query_state inits = {
       .tcache = tcache,
       .state = STATE_NULL,
-      .qterm = TERMINAL_UNKNOWN,
+      .qterm = *detected,
       .cursor_x = -1,
       .cursor_y = -1,
     };

src/lib/termdesc.c

@@ -242,6 +242,14 @@ grow_esc_table(tinfo* ti, const char* tstr, escape_e esc,
   return 0;
 }
 
+// Tertiary Device Attributes, necessary to identify VTE.
+// https://vt100.net/docs/vt510-rm/DA3.html
+// Replies with DCS ! | ... ST
+#define TRIDEVATTR "\x1b[=c"
+
+// Primary Device Attributes, necessary to elicit a response from terminals
+// which don't respond to other queries. All known terminals respond to DA1.
+// https://vt100.net/docs/vt510-rm/DA1.html
 // Device Attributes; replies with (depending on decTerminalID resource):
 //   ⇒  CSI ? 1 ; 2 c  ("VT100 with Advanced Video Option")
 //   ⇒  CSI ? 1 ; 0 c  ("VT101 with No Options")
@@ -252,22 +260,38 @@ grow_esc_table(tinfo* ti, const char* tstr, escape_e esc,
 //   ⇒  CSI ? 6 2 ; Ps c  ("VT220")
 //   ⇒  CSI ? 6 3 ; Ps c  ("VT320")
 //   ⇒  CSI ? 6 4 ; Ps c  ("VT420")
+#define PRIDEVATTR "\x1b[c"
+
+// XTVERSION. Replies with DCS > | ... ST
+#define XTVERSION "\x1b[>0q"
+
+// XTGETTCAP['TN'] (Terminal Name)
+#define XTGETTCAPTN "\x1bP+q544e\x1b\\"
+
+// Secondary Device Attributes, necessary to get Alacritty's version. Since
+// this doesn't uniquely identify a terminal, we ask it last, so that if any
+// queries which *do* unambiguously identify a terminal have succeeded, this
+// needn't be paid attention to.
+// https://vt100.net/docs/vt510-rm/DA2.html
+// Replies with CSI > 6 1 ; Pv ; [01] c
+#define SECDEVATTR "\x1b[>c"
 
 // these three queries (terminated with a Primary Device Attributes, to which
 // all known terminals reply) hopefully can uniquely and unquestionably
 // identify the terminal to which we are talking.
 // FIXME Konsole doesn't currently handle TDA, so we have to consume the 0c
 // in our state machine =[
-#define IDQUERIES "\x1b[=c" /* Tertiary Device Attributes */ \
-                  "\x1b[>0q" /* XTVERSION */ \
-                  "\x1bP+q544e\x1b\\" /* XTGETTCAP['TN'] */
+#define IDQUERIES TRIDEVATTR \
+                  XTVERSION \
+                  XTGETTCAPTN \
+                  SECDEVATTR
 
 // query background, replies in X color https://www.x.org/releases/X11R7.7/doc/man/man7/X.7.xhtml#heading11
-#define CSI_BGQ "\e]11;?\e\\"
+#define CSI_BGQ "\x1b]11;?\e\\"
 
 // FIXME ought be using the u7 terminfo string here, if it exists. the great
 // thing is, if we get a response to this, we know we can use it for u7!
-#define DSRCPR "\e[6n"
+#define DSRCPR "\x1b[6n"
 
 // check for Synchronized Update Mode support. the p is necessary, but Konsole
 // doesn't consume it, so we have to handle that in our state machine =[.
@@ -285,7 +309,7 @@ grow_esc_table(tinfo* ti, const char* tstr, escape_e esc,
                    "\x1b[?1;3;256S" /* try to set 256 cregs */ \
                    CREGSXTSM \
                    GEOMXTSM \
-                   "\x1b[c"         /* Device Attributes */
+                   PRIDEVATTR
 
 // we send an XTSMGRAPHICS to set up 256 color registers (the most we can
 // currently take advantage of; we need at least 64 to use sixel at all.
@@ -381,6 +405,12 @@ apply_term_heuristics(tinfo* ti, const char* termname, int fd,
   }
   if(qterm == TERMINAL_UNKNOWN){
     match_termname(termname, &qterm);
+    // we pick up alacritty's version via a weird hack involving Secondary
+    // Device Attributes. if we're not alacritty, don't trust that version.
+    if(qterm != TERMINAL_ALACRITTY){
+      free(ti->termversion);
+      ti->termversion = NULL;
+    }
   }
   // st had neithercaps.sextants nor caps.quadrants last i checked (0.8.4)
   ti->caps.braille = true; // most everyone has working caps.braille, even from fonts