cgen: string interpolation: optimize away some partial strings of 0 length

vlib/v/gen/cgen.v

@@ -2425,16 +2425,18 @@ fn (mut g Gen) string_inter_literal(node ast.StringInterLiteral) {
 	// Build the string with %
 	mut fieldwidths := []int{}
 	mut specs := []byte{}
-	mut num_fmts := 1
+	mut end_string := false
 	for i, val in node.vals {
 		escaped_val := val.replace_each(['"', '\\"', '\r\n', '\\n', '\n', '\\n', '%', '%%'])
-		g.write(escaped_val)
 		if i >= node.exprs.len {
-			fieldwidths << 0
-			specs << `_`
+			if escaped_val.len > 0 {
+				end_string = true
+				g.write('\\000')
+				g.write(escaped_val)
+			}
 			continue
 		}
-		num_fmts++
+		g.write(escaped_val)
 		sym := g.table.get_type_symbol(node.expr_types[i])
 		sfmt := node.expr_fmts[i]
 		mut fspec := `_` // placeholder
@@ -2507,7 +2509,7 @@ fn (mut g Gen) string_inter_literal(node ast.StringInterLiteral) {
 			if fspec == `p` {
 				g.write('${fmt}p')
 			} else {
-				g.write('${fmt}l${fspec:c}')
+				g.write('${fmt}"PRI${fspec:c}PTR"')
 			}
 		} else if node.expr_types[i].is_int() {
 			if fspec == `c` {
@@ -2533,9 +2535,16 @@ fn (mut g Gen) string_inter_literal(node ast.StringInterLiteral) {
 			// TODO: better check this case
 			g.write('${fmt}"PRId32"')
 		}
+		if i < node.exprs.len - 1 {
 			g.write('\\000')
 		}
-	g.write('", $num_fmts, ')
+	}
+	num_string_parts := if end_string {
+		node.exprs.len+1
+	} else {
+		node.exprs.len
+	}
+	g.write('", $num_string_parts, ')
 	// Build args
 	for i, expr in node.exprs {
 		if node.expr_types[i] == table.string_type {

vlib/v/gen/str.v

@@ -70,7 +70,6 @@ string _STR(const char *fmt, int nfmts, ...) {
 				//v_panic(tos3('Invaid format specifier'));
 			}
 		} else {
-			if (k)
 			_STR_PRINT_ARG(fmt, &buf, &nbytes, &memsize, k);
 		}
 		fmt += k+1;

vlib/v/tests/string_interpolation_test.v

@@ -98,8 +98,10 @@ fn test_inttypes_string_interpolation() {
 	assert '${s:X}:${us:x}:${u16(uc):04x}' == 'A460:d431:00d9'
 	assert '${i:x}:${ui:X}:${int(s):x}' == '9f430000:CBF6EFC7:ffffa460'
 	assert '${l:x}:${ul:X}' == '9537727cad98876c:EF2B7D4001165BD2'
-	// TODO this does not work on Windows
-	// assert '${vp:p}:$bp' == '0xcbf6efc7:0x39e53208c'
+	// default pointer format is platform dependent, so try a few
+	assert '${vp:p}:$bp' == '0xcbf6efc7:0x39e53208c' ||
+		'${vp:p}:$bp' == 'CBF6EFC7:39E53208C' ||
+		'${vp:p}:$bp' == '00000000CBF6EFC7:000000039E53208C'
 }
 
 fn test_utf8_string_interpolation() {
@@ -108,9 +110,9 @@ fn test_utf8_string_interpolation() {
 	m := '10€'
 	assert '$a $st $m' == 'à-côté Sträßle 10€'
 	assert '>${a:10}< >${st:-8}< >${m:5}<-' == '>    à-côté< >Sträßle < >  10€<-'
-	e := '\u20AC' // Eurosign
-	// TODO: this fails with MSVC and tcc
-	// assert '100.00 $e' == '100.00 €'
+	// e := '\u20AC' // Eurosign doesn' work with MSVC and tcc
+	e := '€'
+	assert '100.00 $e' == '100.00 €'
 	m2 := 'Москва́' // cyrillic а́: combination of U+0430 and U+0301, UTF-8: d0 b0 cc 81
 	d := 'Antonín Dvořák' // latin á: U+00E1, UTF-8: c3 a1
 	assert ':${m2:7}:${d:-15}:' == ': Москва́:Antonín Dvořák :'