fix: parse digit-dash root metric names instead of failing as floats (#524)

pkg/parser/parser.go

@@ -612,11 +612,10 @@ func parseExprWithoutPipe(e string) (Expr, string, error) {
 		return nil, "", ErrMissingExpr
 	}
 
-	if '0' <= e[0] && e[0] <= '9' || e[0] == '-' || e[0] == '+' {
-		val, valStr, e, err := parseConst(e)
-		r, _ := utf8.DecodeRuneInString(e)
-		if !unicode.IsLetter(r) {
-			return &expr{val: val, etype: EtConst, valStr: valStr}, e, err
+	if IsDigit(e[0]) || e[0] == '-' || e[0] == '+' {
+		exp, rest, ok := parseConstExpr(e)
+		if ok {
+			return exp, rest, nil
 		}
 	}
 
@@ -655,6 +654,25 @@ func parseExprWithoutPipe(e string) (Expr, string, error) {
 	return &expr{target: name}, e, nil
 }
 
+func parseConstExpr(e string) (*expr, string, bool) {
+	val, valStr, rest, err := parseConst(e)
+	if err != nil {
+		// A failure means the greedily-slurped run of [0-9.+-eE] characters is
+		// not a valid float, e.g. a root metric name like "587-AL". Let the
+		// caller parse the original token as a metric name instead.
+		return nil, e, false
+	}
+
+	if rest != "" {
+		r, size := utf8.DecodeRuneInString(rest)
+		if size > 0 && unicode.IsLetter(r) {
+			return nil, e, false
+		}
+	}
+
+	return &expr{val: val, etype: EtConst, valStr: valStr}, rest, true
+}
+
 func parseExprInner(e string) (Expr, string, error) {
 	exp, e, err := parseExprWithoutPipe(e)
 	if err != nil {

pkg/parser/parser_test.go

@@ -165,6 +165,58 @@ func TestParseExpr(t *testing.T) {
 			},
 		},
 
+		// Issue #524: a root metric name that starts with one or more digits
+		// followed by a dash (e.g. "587-AL") must parse as a metric name, the
+		// same as graphite-web, instead of failing ParseFloat on "587-".
+		{
+			"587-AL.random.a",
+			&expr{target: "587-AL.random.a"},
+		},
+		{
+			"587-AL",
+			&expr{target: "587-AL"},
+		},
+		// Guard against over-correction: these already parsed as names and
+		// must keep doing so.
+		{
+			"AAA-587",
+			&expr{target: "AAA-587"},
+		},
+		{
+			"587AAA",
+			&expr{target: "587AAA"},
+		},
+		{
+			"AAA587",
+			&expr{target: "AAA587"},
+		},
+		// Genuine numeric constants must still parse as EtConst.
+		{
+			"-1",
+			&expr{val: -1, etype: EtConst, valStr: "-1"},
+		},
+		{
+			"+2.5",
+			&expr{val: 2.5, etype: EtConst, valStr: "+2.5"},
+		},
+		{
+			"1e3",
+			&expr{val: 1000, etype: EtConst, valStr: "1e3"},
+		},
+		// A function call with a digit-dash series arg parses without error and
+		// preserves the inner metric name.
+		{
+			"sumSeries(587-AL.random.*)",
+			&expr{
+				target: "sumSeries",
+				etype:  EtFunc,
+				args: []*expr{
+					{target: "587-AL.random.*"},
+				},
+				argString: "587-AL.random.*",
+			},
+		},
+
 		{
 			"func1(metric1, -3 , 'foo' )",
 			&expr{