Flagsify EscapeStyle and make ESCAPE_BACKSLASH_ONELINE implicit

I want to tweak behaviour further, and that'll be easier when "style"
is converted to a bitfield.

Some callers used ESCAPE_BACKSLASH_ONELINE, and others not. But the
ones that didn't, simply didn't care, because the argument was assumed to
be one-line anyway (e.g. a service name). In environment-generator, this
could make a difference. But I think it's better to escape the newlines
there too. So newlines are now always escaped, to simplify the code and
the test matrix.

src/basic/escape.c

@@ -494,7 +494,7 @@ char* shell_escape(const char *s, const char *bad) {
         return r;
 }
 
-char* shell_maybe_quote(const char *s, EscapeStyle style) {
+char* shell_maybe_quote(const char *s, ShellEscapeFlags flags) {
         const char *p;
         char *r, *t;
 
@@ -513,36 +513,27 @@ char* shell_maybe_quote(const char *s, EscapeStyle style) {
         if (!*p)
                 return strdup(s);
 
-        r = new(char, (style == ESCAPE_POSIX) + 1 + strlen(s)*2 + 1 + 1);
+        r = new(char, FLAGS_SET(flags, SHELL_ESCAPE_POSIX) + 1 + strlen(s)*2 + 1 + 1);
         if (!r)
                 return NULL;
 
         t = r;
-        switch (style) {
-        case ESCAPE_BACKSLASH:
-        case ESCAPE_BACKSLASH_ONELINE:
-                *(t++) = '"';
-                break;
-        case ESCAPE_POSIX:
+        if (FLAGS_SET(flags, SHELL_ESCAPE_POSIX)) {
                 *(t++) = '$';
                 *(t++) = '\'';
-                break;
-        default:
-                assert_not_reached("Bad EscapeStyle");
-        }
+        } else
+                *(t++) = '"';
 
         t = mempcpy(t, s, p - s);
 
-        if (IN_SET(style, ESCAPE_BACKSLASH, ESCAPE_BACKSLASH_ONELINE))
-                t = strcpy_backslash_escaped(t, p, SHELL_NEED_ESCAPE,
-                                             style == ESCAPE_BACKSLASH_ONELINE);
-        else
-                t = strcpy_backslash_escaped(t, p, SHELL_NEED_ESCAPE_POSIX, true);
+        t = strcpy_backslash_escaped(t, p,
+                                     FLAGS_SET(flags, SHELL_ESCAPE_POSIX) ? SHELL_NEED_ESCAPE_POSIX : SHELL_NEED_ESCAPE,
+                                     true);
 
-        if (IN_SET(style, ESCAPE_BACKSLASH, ESCAPE_BACKSLASH_ONELINE))
-                *(t++) = '"';
-        else
+        if (FLAGS_SET(flags, SHELL_ESCAPE_POSIX))
                 *(t++) = '\'';
+        else
+                *(t++) = '"';
         *t = 0;
 
         return r;

src/basic/escape.h

@@ -33,15 +33,12 @@ typedef enum UnescapeFlags {
         UNESCAPE_ACCEPT_NUL = 1 << 1,
 } UnescapeFlags;
 
-typedef enum EscapeStyle {
-        ESCAPE_BACKSLASH         = 1,  /* Add shell quotes ("") so the shell will consider this a single
-                                          argument, possibly multiline. Tabs and newlines are not escaped. */
-        ESCAPE_BACKSLASH_ONELINE = 2,  /* Similar to ESCAPE_BACKSLASH, but always produces a single-line
-                                          string instead. Shell escape sequences are produced for tabs and
-                                          newlines. */
-        ESCAPE_POSIX             = 3,  /* Similar to ESCAPE_BACKSLASH_ONELINE, but uses POSIX shell escape
-                                        * syntax (a string enclosed in $'') instead of plain quotes. */
-} EscapeStyle;
+typedef enum ShellEscapeFlags {
+        /* The default is to add shell quotes ("") so the shell will consider this a single argument.
+         * Tabs and newlines are escaped. */
+
+        SHELL_ESCAPE_POSIX = 1 << 1, /* Use POSIX shell escape syntax (a string enclosed in $'') instead of plain quotes. */
+} ShellEscapeFlags;
 
 char* cescape(const char *s);
 char* cescape_length(const char *s, size_t n);
@@ -64,4 +61,4 @@ char* octescape(const char *s, size_t len);
 char* escape_non_printable_full(const char *str, size_t console_width, bool eight_bit);
 
 char* shell_escape(const char *s, const char *bad);
-char* shell_maybe_quote(const char *s, EscapeStyle style);
+char* shell_maybe_quote(const char *s, ShellEscapeFlags flags);