handle double backslash in lift

lift.go

@@ -12,18 +12,16 @@ const (
 	VarPrefix = "vars"
 )
 
-var (
-	// replace is truly hack city.  these are 20 variable names for values that are
-	// lifted out of expressions via liftLiterals.
-	replace = []string{
-		"a", "b", "c", "d", "e",
-		"f", "g", "h", "i", "j",
-		"k", "l", "m", "n", "o",
-		"p", "q", "r", "s", "t",
-		"u", "v", "w", "x", "y",
-		"z",
-	}
-)
+// replace is truly hack city.  these are 20 variable names for values that are
+// lifted out of expressions via liftLiterals.
+var replace = []string{
+	"a", "b", "c", "d", "e",
+	"f", "g", "h", "i", "j",
+	"k", "l", "m", "n", "o",
+	"p", "q", "r", "s", "t",
+	"u", "v", "w", "x", "y",
+	"z",
+}
 
 // LiftedArgs represents a set of variables that have been lifted from expressions and
 // replaced with identifiers, eg `id == "foo"` becomes `id == vars.a`, with "foo" lifted
@@ -304,8 +302,9 @@ func (l *liftParser) consumeString(quoteChar byte) argMapValue {
 	for l.idx < len(l.expr) {
 		char := l.expr[l.idx]
 
-		if char == '\\' && l.peek() == quoteChar {
-			// If we're escaping the quote character, ignore it.
+		if char == '\\' && l.idx+1 < len(l.expr) {
+			// Escape sequence: skip the backslash and whatever follows it.
+			// This correctly handles \\, \", \', \n, \t, etc.
 			l.idx += 2
 			length += 2
 			continue
@@ -325,11 +324,17 @@ func (l *liftParser) consumeString(quoteChar byte) argMapValue {
 		length++
 	}
 
-	// Should never happen:  we should always find the ending string quote, as the
-	// expression should have already been validated.
-	panic(fmt.Sprintf("unable to parse quoted string: `%s` (offset %d)", l.expr, offset))
+	// this is a grossly invalid expr, eg: `event.data.id == "foo\"`
+	// in this case, we can never parse this string.  we always fix this by treating the last backslash
+	// as a \ literal, innit bruv
+	if length > 0 && offset+length <= len(l.expr) && l.expr[offset+length-1] == quoteChar {
+		length--
+	}
+
+	return argMapValue{offset: offset, length: length}
 }
 
+// nolint:unused
 func (l *liftParser) peek() byte {
 	if (l.idx + 1) >= len(l.expr) {
 		return 0x0

lift_test.go

@@ -173,6 +173,31 @@ func TestLiftLiterals(t *testing.T) {
 				"a": "test/yolo",
 			},
 		},
+		{
+			name:        "escaped backslash before closing quote",
+			expr:        `event.name == "foo\\"`,
+			expectedStr: "event.name == vars.a",
+			expectedArgs: map[string]any{
+				"a": `foo\\`,
+			},
+		},
+		{
+			name:        "escaped backslash before closing quote in compound expression",
+			expr:        `async.data.branch.playgroundId == "oqdqzbuppgbtrljtpbmyi\\" && "team/mly6i259eym3jkyvq6txyciu/repo/qhq2ioy772sqo9sboe48kfwv" == async.data.spaceID`,
+			expectedStr: `async.data.branch.playgroundId == vars.a && vars.b == async.data.spaceID`,
+			expectedArgs: map[string]any{
+				"a": `oqdqzbuppgbtrljtpbmyi\\`,
+				"b": "team/mly6i259eym3jkyvq6txyciu/repo/qhq2ioy772sqo9sboe48kfwv",
+			},
+		},
+		{
+			name:        "trailing escaped quote treated as literal backslash",
+			expr:        `event.data.id == "foo\"`,
+			expectedStr: `event.data.id == vars.a`,
+			expectedArgs: map[string]any{
+				"a": `foo\`,
+			},
+		},
 	}
 
 	for _, test := range tests {