From 87216cff63c2381a35cd0f365a448f9f567859af Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marco=20B=C3=B6ttcher?=
 <34623283+spacesinmotion@users.noreply.github.com>
Date: Thu, 15 Aug 2019 11:41:23 +0200
Subject: [PATCH] compiler:  '\$'  escape

---
 compiler/scanner.v                         | 16 ++++++++++++++--
 compiler/tests/string_interpolation_test.v | 17 +++++++++++++++++
 2 files changed, 31 insertions(+), 2 deletions(-)
 create mode 100644 compiler/tests/string_interpolation_test.v

diff --git a/compiler/scanner.v b/compiler/scanner.v
index e125d133ef..9b93be354f 100644
--- a/compiler/scanner.v
+++ b/compiler/scanner.v
@@ -569,6 +569,18 @@ fn (s &Scanner) error(msg string) {
 	exit(1)
 }
 
+
+fn (s Scanner) count_symbol_before(p int, sym byte) int {
+  mut count := 0
+  for i:=p; i>=0; i-- {
+    if s.text[i] != sym {
+      break
+    }
+    count++
+  }
+  return count
+}
+
 // println('array out of bounds $idx len=$a.len')
 // This is really bad. It needs a major clean up
 fn (s mut Scanner) ident_string() string {
@@ -601,14 +613,14 @@ fn (s mut Scanner) ident_string() string {
 			s.error('0 character in a string literal')
 		}
 		// ${var}
-		if c == `{` && prevc == `$` {
+		if c == `{` && prevc == `$` && s.count_symbol_before(s.pos-2, `\\`) % 2 == 0 {
 			s.inside_string = true
 			// so that s.pos points to $ at the next step
 			s.pos -= 2
 			break
 		}
 		// $var
-		if (c.is_letter() || c == `_`) && prevc == `$` {
+		if (c.is_letter() || c == `_`) && prevc == `$` && s.count_symbol_before(s.pos-2, `\\`) % 2 == 0 {
 			s.inside_string = true
 			s.dollar_start = true
 			s.pos -= 2
diff --git a/compiler/tests/string_interpolation_test.v b/compiler/tests/string_interpolation_test.v
new file mode 100644
index 0000000000..cda819000f
--- /dev/null
+++ b/compiler/tests/string_interpolation_test.v
@@ -0,0 +1,17 @@
+
+fn test_excape_dollar_in_string() {
+  i := 42
+
+  assert '($i)' == '(42)'
+  assert '(\$i)'.contains('i') && !'(\$i)'.contains('42')
+  assert !'(\\$i)'.contains('i') && '(\\$i)'.contains('42') && '(\\$i)'.contains('\\')
+  assert '(\\\$i)'.contains('i') && !'(\\\$i)'.contains('42') && '(\\$i)'.contains('\\')
+  assert !'(\\\\$i)'.contains('i') && '(\\\\$i)'.contains('42') && '(\\\\$i)'.contains('\\\\')
+
+  assert '(${i})' == '(42)'
+  assert '(\${i})'.contains('i') && !'(\${i})'.contains('42')
+  assert !'(\\${i})'.contains('i') && '(\\${i})'.contains('42') && '(\\${i})'.contains('\\')
+  assert '(\\\${i})'.contains('i') && !'(\\\${i})'.contains('42') && '(\\${i})'.contains('\\')
+  assert !'(\\\\${i})'.contains('i') && '(\\\\${i})'.contains('42') && '(\\\\${i})'.contains('\\\\')
+  assert i==42
+}