dcs: xtgettcap: always reply with tigetstr(3) formatted "strings"

That is, instead of sometimes replying with a "source" encoded
string (where e.g. '\E' are returned just like that, and not as an
actual ESC), always unescape all string values.

This also includes \n \r \t \b \f \s, \^ \\ \ \:, as well as ^x-styled
escapes.

Closes #1701

CHANGELOG.md

@@ -55,6 +55,21 @@
 ## Unreleased
 ### Added
 ### Changed
+
+* All `XTGETTCAP` capabilities are now in the `tigetstr()` format:
+
+  - parameterized string capabilities were previously "source
+    encoded", meaning e.g. `\E` where not "decoded" into `\x1b`.
+  - Control characters were also "source encoded", meaning they were
+    returned as e.g. "^G" instead of `\x07` ([#1701][1701]).
+
+  In other words, if, after this change, `XTGETTCAP` returns a string
+  that is different compared to `tigetstr()`, then it is likely a bug
+  in foot's implementation of `XTGETTCAP`.
+
+[1701]: https://codeberg.org/dnkl/foot/issues/1701
+
+
 ### Deprecated
 ### Removed
 ### Fixed

scripts/generate-builtin-terminfo.py

@@ -50,27 +50,33 @@ class IntCapability(Capability):
 
 class StringCapability(Capability):
     def __init__(self, name: str, value: str):
-       # Expand \E to literal ESC in non-parameterized capabilities
-        if '%' not in value:
-            # Ensure e.g. \E7 doesn’t get translated to “\0337”, which
-            # would be interpreted as octal 337 by the C compiler
-            value = re.sub(r'\\E([0-7])', r'\\033" "\1', value)
+        # see terminfo(5) for valid escape sequences
 
-            # Replace \E with an actual escape
-            value = re.sub(r'\\E', r'\\033', value)
+        # Control characters
+        def translate_ctrl_chr(m):
+            ctrl = m.group(1)
+            if ctrl == '?':
+                return chr(0x7f)
+            return chr(ord(ctrl) - ord('@'))
+        value = re.sub('\^([@A-Z[\\\\\]^_?])', translate_ctrl_chr, value)
 
-            # Don’t escape ‘:’
-            value = value.replace('\\:', ':')
+        # Ensure e.g. \E7 (or \e7) doesn’t get translated to “\0337”,
+        # which would be interpreted as octal 337 by the C compiler
+        value = re.sub(r'(\\E|\\e)([0-7])', r'\\033" "\2', value)
 
-        else:
-            value = value.replace("\\", "\\\\")
-            # # Need to double-escape backslashes. These only occur in
-            # # ‘\E\’ combos. Note that \E itself is updated below
-            # value = value.replace('\\E\\\\', '\\E\\\\\\\\')
+        # Replace \E and \e with ESC
+        value = re.sub(r'\\E|\\e', r'\\033', value)
 
-            # # Need to double-escape \E in C string literals
-            # value = value.replace('\\E', '\\\\E')
+        # Unescape ,:^
+        value = re.sub(r'\\(,|:|\^)', r'\1', value)
 
+        # Replace \s with space
+        value = value.replace('\\s', ' ')
+
+        # Let \\, \n, \r, \t, \b and \f "fall through", to the C string literal
+
+        if re.search(r'\\l', value):
+            raise NotImplementedError('\\l escape sequence')
 
         super().__init__(name, value)
 

utils/xtgettcap.c

@@ -103,7 +103,7 @@ main(int argc, const char *const *argv)
             if (isprint(buf[i]))
                 printf("%c", buf[i]);
             else if (buf[i] == '\033')
-                printf("\033[1;31m\\E\033[m");
+                printf("\033[1;31m<ESC>\033[m");
             else
                 printf("%02x", (uint8_t)buf[i]);
         }
@@ -158,12 +158,30 @@ main(int argc, const char *const *argv)
 
                 printf("  \033[%dm", color);
                 for (size_t i = 0 ; i < len; i++) {
-                    if (isprint(decoded[i]))
+                    if (isprint(decoded[i])) {
+                        /* All printable characters */
                         printf("%c", decoded[i]);
-                    else if (decoded[i] == '\033')
-                        printf("\033[1;31m\\E\033[22;%dm", color);
-                    else
+                    }
+
+                    else if (decoded[i] == '\033') {
+                        /* ESC */
+                        printf("\033[1;31m<ESC>\033[22;%dm", color);
+                    }
+
+                    else if (decoded[i] >= '\x00' && decoded[i] <= '\x5f') {
+                        /* Control characters, e.g. ^G etc */
+                        printf("\033[1m^%c\033[22m", decoded[i] + '@');
+                    }
+
+                    else if (decoded[i] == '\x7f') {
+                        /* Control character ^? */
+                        printf("\033[1m^?\033[22m");
+                    }
+
+                    else {
+                        /* Unknown: print hex representation */
                         printf("\033[1m%02x\033[22m", (uint8_t)decoded[i]);
+                    }
                 }
                 printf("\033[m\r\n");
                 replies++;