bkpr-report: enhance tag syntax from {tag:replacement} to {tag?if-set:if-not-set}

This is more powerful, but we need to do this before release.  It lets
us do things like: {credit?+{credit}:0} to only put a `+` in front of
no-zero credit, and {txid?TXID {txid}:Outpoint {outpoint}} to print
either `TXID xxx` or `Outpoint xxx`.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: rustyrussell

contrib/msggen/msggen/schema.json

@@ -5160,15 +5160,16 @@
               "{currencydebit}: debit amount converted into bkpr-currency",
               "{currencycreditdebit}: +credit or -debit (or 0) in bkpr-currency",
               "",
-              "If a field is unavailable, it expands to an empty string.",
+              "If a field is unavailable, it expands to an empty string (or 0 for credit, debit, fees and creditdebit).",
               "",
-              "You can provide fallback with ?, which is used when the tag is not present (or zero, for credit, debit, fees and creditdebit).  This fallback can include more tags:",
-              " * {outpoint?NONE}",
-              " * {payment_id?txid: {txid?UNKNOWN}}",
-              "The first one the outpoint, or NONE if that is not available. ",
-              "The second prints the payment_id, or if that is not available, the string 'txid: ' followed by the txid, or if that is not available, 'txid: UNKNOWN'.",
-              "",
-              "The text after ? is used only if that tag would otherwise be empty.",
+              "Tags support C-style conditional syntax: {tag[?if-set][:if-not-set]}",
+              " * if-set: text to use when the tag is present (and non-zero for credit, debit, fees and creditdebit).  Default is the tag value itself.",
+              " * if-not-set: text to use when the tag is absent (or zero for amount fields).  Default is empty string (or 0 for amount fields).",
+              "Either or both parts may be omitted, and each part can itself contain tags.  For example:",
+              " * {outpoint:NONE}: the outpoint value, or 'NONE' if not available",
+              " * {credit:0.00}: the credit value, or '0.00' if zero",
+              " * {outpoint?[{outpoint}]:NONE}: '[<value>]' if outpoint is available, or 'NONE' if not",
+              " * {payment_id:{txid:UNKNOWN}}: the payment_id, or the txid if no payment_id, or 'UNKNOWN' if neither",
               "",
               "To include a literal {, write {{."
             ]

doc/schemas/bkpr-report.json

@@ -46,15 +46,16 @@
           "{currencydebit}: debit amount converted into bkpr-currency",
           "{currencycreditdebit}: +credit or -debit (or 0) in bkpr-currency",
           "",
-          "If a field is unavailable, it expands to an empty string.",
+          "If a field is unavailable, it expands to an empty string (or 0 for credit, debit, fees and creditdebit).",
           "",
-          "You can provide fallback with ?, which is used when the tag is not present (or zero, for credit, debit, fees and creditdebit).  This fallback can include more tags:",
-          " * {outpoint?NONE}",
-          " * {payment_id?txid: {txid?UNKNOWN}}",
-          "The first one the outpoint, or NONE if that is not available. ",
-          "The second prints the payment_id, or if that is not available, the string 'txid: ' followed by the txid, or if that is not available, 'txid: UNKNOWN'.",
-          "",
-          "The text after ? is used only if that tag would otherwise be empty.",
+          "Tags support C-style conditional syntax: {tag[?if-set][:if-not-set]}",
+          " * if-set: text to use when the tag is present (and non-zero for credit, debit, fees and creditdebit).  Default is the tag value itself.",
+          " * if-not-set: text to use when the tag is absent (or zero for amount fields).  Default is empty string (or 0 for amount fields).",
+          "Either or both parts may be omitted, and each part can itself contain tags.  For example:",
+          " * {outpoint:NONE}: the outpoint value, or 'NONE' if not available",
+          " * {credit:0.00}: the credit value, or '0.00' if zero",
+          " * {outpoint?[{outpoint}]:NONE}: '[<value>]' if outpoint is available, or 'NONE' if not",
+          " * {payment_id:{txid:UNKNOWN}}: the payment_id, or the txid if no payment_id, or 'UNKNOWN' if neither",
           "",
           "To include a literal {, write {{."
         ]

plugins/bkpr/report.c

@@ -220,8 +220,10 @@ struct report_format {
 			    const struct bkpr *bkpr,
 			    const struct income_event *e);
 	const char **str;
-	/* If fmt returns NULL, evaluate these instead. */
-	struct report_format **alt;
+	/* If fmt returns non-NULL (and non-ZERO_AMOUNT), evaluate these instead of the value. */
+	struct report_format **ifset;
+	/* If fmt returns NULL (or ZERO_AMOUNT when either ifset/ifnotset is non-NULL), evaluate these. */
+	struct report_format **ifnotset;
 };
 
 static void add_literal(struct report_format *f,
@@ -231,15 +233,18 @@ static void add_literal(struct report_format *f,
 		tal_arr_expand(&f->fmt, NULL);
 		tal_arr_expand(&f->str,
 			       tal_strndup(f->str, *start, end - *start));
-		tal_arr_expand(&f->alt, NULL);
+		tal_arr_expand(&f->ifset, NULL);
+		tal_arr_expand(&f->ifnotset, NULL);
 		*start = end;
 	}
 }
 
+/* alt_term is a secondary loop terminator (in addition to term); '\0' means none. */
 static struct report_format *
 parse_report_format(const tal_t *ctx,
 		    const char **start,
 		    char term,
+		    char alt_term,
 		    const char **err)
 {
 	const char *p;
@@ -248,11 +253,12 @@ parse_report_format(const tal_t *ctx,
 	f = tal(ctx, struct report_format);
 	f->fmt = tal_arr(f, typeof(*f->fmt), 0);
 	f->str = tal_arr(f, const char *, 0);
-	f->alt = tal_arr(f, struct report_format *, 0);
+	f->ifset = tal_arr(f, struct report_format *, 0);
+	f->ifnotset = tal_arr(f, struct report_format *, 0);
 
 	p = *start;
-	while (*p != term) {
-		struct report_format *alt;
+	while (*p != term && !(alt_term && *p == alt_term)) {
+		struct report_format *ifset, *ifnotset;
 		const struct report_tag *rt;
 
 		if (*p == '\0') {
@@ -273,7 +279,8 @@ parse_report_format(const tal_t *ctx,
 			lit = tal_strcat(tmpctx, take(lit), "{");
 			tal_arr_expand(&f->fmt, NULL);
 			tal_arr_expand(&f->str, lit);
-			tal_arr_expand(&f->alt, NULL);
+			tal_arr_expand(&f->ifset, NULL);
+			tal_arr_expand(&f->ifnotset, NULL);
 			p += 2;
 			*start = p;
 			continue;
@@ -282,7 +289,7 @@ parse_report_format(const tal_t *ctx,
 		/* Emit preceding literal, if any. */
 		add_literal(f, start, p);
 
-		const char *endtag = p + 1 + strcspn(p+1, "?}");
+		const char *endtag = p + 1 + strcspn(p+1, "?:}");
 		if (*endtag == '\0') {
 			*err = tal_fmt(ctx, "Unterminated tag %s", p + 1);
 			return tal_free(f);
@@ -296,25 +303,45 @@ parse_report_format(const tal_t *ctx,
 			return tal_free(f);
 		}
 
+		ifset = ifnotset = NULL;
 		if (*endtag == '?') {
+			/* Parse if-set, which ends at ':' or '}' */
 			*start = endtag + 1;
-			alt = parse_report_format(f, start, '}', err);
-			if (!alt) {
-				/* Steal error upwards! */
+			ifset = parse_report_format(f, start, '}', ':', err);
+			if (!ifset) {
 				tal_steal(ctx, *err);
 				return tal_free(f);
 			}
-			/* Consume final } */
+			if (**start == ':') {
+				/* Parse if-not-set */
+				(*start)++;
+				ifnotset = parse_report_format(f, start, '}', '\0', err);
+				if (!ifnotset) {
+					tal_steal(ctx, *err);
+					return tal_free(f);
+				}
+			}
+			/* Consume final '}' */
+			(*start)++;
+		} else if (*endtag == ':') {
+			/* Only if-not-set */
+			*start = endtag + 1;
+			ifnotset = parse_report_format(f, start, '}', '\0', err);
+			if (!ifnotset) {
+				tal_steal(ctx, *err);
+				return tal_free(f);
+			}
+			/* Consume final '}' */
 			(*start)++;
 		} else {
 			assert(*endtag == '}');
-			alt = NULL;
 			*start = endtag + 1;
 		}
 
 		tal_arr_expand(&f->fmt, rt->fmt);
 		tal_arr_expand(&f->str, NULL);
-		tal_arr_expand(&f->alt, alt);
+		tal_arr_expand(&f->ifset, ifset);
+		tal_arr_expand(&f->ifnotset, ifnotset);
 
 		p = *start;
 	}
@@ -336,7 +363,7 @@ struct command_result *param_report_format(struct command *cmd,
 	if (ret)
 		return ret;
 
-	*format = parse_report_format(cmd, &start, '\0', &err);
+	*format = parse_report_format(cmd, &start, '\0', '\0', &err);
 	if (!*format)
 		return command_fail_badparam(cmd, name, buffer, tok, err);
 
@@ -420,19 +447,24 @@ static char *format_event(const tal_t *ctx,
 		}
 
 		v = fmt->fmt[i](tmpctx, bkpr, e);
-		/* If there's an alternative, we treat ZERO_AMOUNT as missing. */
-		if (v == ZERO_AMOUNT && fmt->alt[i])
+		/* Treat ZERO_AMOUNT as absent when there are conditionals. */
+		if (v == ZERO_AMOUNT && (fmt->ifset[i] || fmt->ifnotset[i]))
 			v = NULL;
 
 		if (v) {
-			v = escape_value(tmpctx, v, esc);
-			out = tal_strcat(ctx, take(out), v);
+			if (fmt->ifset[i]) {
+				out = tal_strcat(ctx, take(out),
+						 format_event(tmpctx, fmt->ifset[i], esc, bkpr, e));
+			} else {
+				out = tal_strcat(ctx, take(out),
+						 escape_value(tmpctx, v, esc));
+			}
 			continue;
 		}
 
-		if (fmt->alt[i]) {
-			char *alt = format_event(tmpctx, fmt->alt[i], esc, bkpr, e);
-			out = tal_strcat(ctx, take(out), alt);
+		if (fmt->ifnotset[i]) {
+			out = tal_strcat(ctx, take(out),
+					 format_event(tmpctx, fmt->ifnotset[i], esc, bkpr, e));
 		}
 	}