protoc-gen-go: normalize floating-point default values (#737)

Parse floating-point default values and format them with fmt.Sprint.
Eliminates a minor point of inconsistency with the v2 generator.

Change-Id: I153318f1760bac878cb0303301bed7e4bafe3431
Cherry-Pick: github.com/golang/protobuf@d3de96c4c28ef8af3aa1a892fc481e0f103c01ff
Original-Author: Damien Neil <neild@users.noreply.github.com>
Reviewed-on: https://go-review.googlesource.com/c/151429
Reviewed-by: Damien Neil <dneil@google.com>

protoc-gen-go/generator/generator.go

@@ -1537,6 +1537,18 @@ func (g *Generator) goTag(message *Descriptor, field *descriptor.FieldDescriptor
 				g.Fail("unknown enum type", CamelCaseSlice(obj.TypeName()))
 			}
 			defaultValue = enum.integerValueAsString(defaultValue)
+		case descriptor.FieldDescriptorProto_TYPE_FLOAT:
+			if def := defaultValue; def != "inf" && def != "-inf" && def != "nan" {
+				if f, err := strconv.ParseFloat(defaultValue, 32); err == nil {
+					defaultValue = fmt.Sprint(float32(f))
+				}
+			}
+		case descriptor.FieldDescriptorProto_TYPE_DOUBLE:
+			if def := defaultValue; def != "inf" && def != "-inf" && def != "nan" {
+				if f, err := strconv.ParseFloat(defaultValue, 64); err == nil {
+					defaultValue = fmt.Sprint(f)
+				}
+			}
 		}
 		defaultValue = ",def=" + defaultValue
 	}
@@ -2236,6 +2248,14 @@ func (g *Generator) generateDefaultConstants(mc *msgCtx, topLevelFields []topLev
 				def = "float32(" + def + ")"
 			}
 			kind = "var "
+		case df.getProtoType() == descriptor.FieldDescriptorProto_TYPE_FLOAT:
+			if f, err := strconv.ParseFloat(def, 32); err == nil {
+				def = fmt.Sprint(float32(f))
+			}
+		case df.getProtoType() == descriptor.FieldDescriptorProto_TYPE_DOUBLE:
+			if f, err := strconv.ParseFloat(def, 64); err == nil {
+				def = fmt.Sprint(f)
+			}
 		case df.getProtoType() == descriptor.FieldDescriptorProto_TYPE_ENUM:
 			// Must be an enum.  Need to construct the prefixed name.
 			obj := g.ObjectNamed(df.getProtoTypeName())

protoc-gen-go/testdata/my_test/test.proto

@@ -85,6 +85,13 @@ message Request {
   optional int32 reset = 12;
   // This field should not conflict with any getters.
   optional string get_key = 16;
+
+  optional float float_ninf = 20 [default=-inf];
+  optional float float_pinf = 21 [default=inf];
+  optional float float_exp = 22 [default=1e9];
+  optional double double_ninf = 23 [default=-inf];
+  optional double double_pinf = 24 [default=inf];
+  optional double double_exp = 25 [default=1e9];
 }
 
 message Reply {