Refine numeric literal syntax

Leading zeros are no longer permitted in decimal literals, which is
technically a backwards-incompatible change, but I consider it to be
something like a bug fix. Anyway, the project is unlikely to have any
users that would be impacted.

2 files changed, 36 insertions, 6 deletions

diff --git a/asspb.go b/asspb.go
index f8036f8..624f3ca 100644
--- a/asspb.go
+++ b/asspb.go
@@ -18,8 +18,8 @@
 // # Numbers
 //
 // Numbers are written in base 10 and can optionally have a fractional part or
-// an exponent written with "e". As a special case, a number prefixed with "0x"
-// can be written in base 16.
+// an exponent written with "e" or "E". As a special case, a number prefixed
+// with "0x" or "0X" can be written in base 16.
 //
 //	100
 //	-30
@@ -28,6 +28,9 @@
 //	13.5
 //	1e100
 //
+// Leading zeros are not permitted in decimal numbers, due to potential
+// confusion with octal (which is not supported).
+//
 // # Strings
 //
 // Strings are written with " or ' and any sequence of intermediate bytes (with
@@ -189,7 +192,7 @@ func (p *parser) parseLit(s string) bool {
 	return false
 }
 
-var numRE = regexp.MustCompile(`^-?(0x[0-9a-fA-F]+|([0-9]+(\.[0-9]*)?|\.[0-9]+)(e-?[0-9]+)?)`)
+var numRE = regexp.MustCompile(`^[-+]?(0[xX][0-9a-fA-F]+|((0|[1-9][0-9]*)(\.[0-9]*)?|\.[0-9]+)([eE][-+]?[0-9]+)?)`)
 
 func (p *parser) parseNum() (any, bool) {
 	p.skipSpace()
@@ -197,7 +200,7 @@ func (p *parser) parseNum() (any, bool) {
 	if numBytes == nil {
 		return nil, false
 	}
-	if bytes.ContainsAny(numBytes, ".e") {
+	if bytes.ContainsAny(numBytes, ".eE") {
 		n, err := strconv.ParseFloat(string(numBytes), 64)
 		if err != nil {
 			return nil, false
@@ -205,8 +208,8 @@ func (p *parser) parseNum() (any, bool) {
 		p.i += len(numBytes)
 		return n, true
 	}
-	if b, ok := bytes.CutPrefix(numBytes, []byte("0x")); ok {
-		n, err := strconv.ParseInt(string(b), 16, 64)
+	if bytes.HasPrefix(numBytes, []byte("0x")) || bytes.HasPrefix(numBytes, []byte("0X")) {
+		n, err := strconv.ParseInt(string(numBytes[2:]), 16, 64)
 		if err != nil {
 			return nil, false
 		}
diff --git a/asspb_test.go b/asspb_test.go
index 7600dee..2425571 100644
--- a/asspb_test.go
+++ b/asspb_test.go
@@ -43,18 +43,38 @@ field_repeated [5, 6]
 can just span multiple lines"`,
 		want: map[string]any{"field": "strings\ncan just span multiple lines"},
 	}, {
+		desc: "Zero",
+		msg:  `field: 0`,
+		want: map[string]any{"field": 0.},
+	}, {
 		desc: "Hex",
 		msg:  `field: 0xff`,
 		want: map[string]any{"field": 255.},
 	}, {
+		desc: "CapitalHex",
+		msg:  `field: 0XfF`,
+		want: map[string]any{"field": 255.},
+	}, {
+		desc: "HexLeadingZero",
+		msg:  `field: 0x0f`,
+		want: map[string]any{"field": 15.},
+	}, {
 		desc: "Float",
 		msg:  `field: 1.5e10`,
 		want: map[string]any{"field": 1.5e10},
 	}, {
+		desc: "FloatCapitalE",
+		msg:  `field: 1.5E10`,
+		want: map[string]any{"field": 1.5e10},
+	}, {
 		desc: "NegativeFloat",
 		msg:  `field: -1.5e-10`,
 		want: map[string]any{"field": -1.5e-10},
 	}, {
+		desc: "PositiveFloat",
+		msg:  `field: +1.5e+10`,
+		want: map[string]any{"field": 1.5e10},
+	}, {
 		desc: "Int",
 		msg:  `field: 10`,
 		want: map[string]any{"field": 10.},
@@ -63,6 +83,10 @@ can just span multiple lines"`,
 		msg:  `field: -10`,
 		want: map[string]any{"field": -10.},
 	}, {
+		desc: "PositiveInt",
+		msg:  `field: +10`,
+		want: map[string]any{"field": 10.},
+	}, {
 		desc: "String",
 		msg:  `field: 'asdf'`,
 		want: map[string]any{"field": "asdf"},
@@ -238,6 +262,9 @@ func TestUnmarshal_Invalid(t *testing.T) {
 	}, {
 		desc: "ListBadMsgVal",
 		msg:  `field [{asdf}]`,
+	}, {
+		desc: "IntLeadingZero",
+		msg:  `field: 0644`,
 	}} {
 		t.Run(tc.desc, func(t *testing.T) {
 			t.Parallel()