Only apply 'field.id.{negative,zero}' to explicit field IDs (#50)

Auto-assigned field IDs start at zero and then go negative. If auto-
assigned fields are intentionally used (i.e. no `field.id.missing`
check), then it's not helpful to report additional errors about the
range of the auto-assigned values.

These checks now only report errors for explicitly assigned field IDs.

README.md

@@ -94,13 +94,13 @@ implicit/auto-assigning syntax).
 
 ### `field.id.negative`
 
-This check reports an error if a field's ID is negative.
+This check reports an error if a field's ID is explicitly negative.
 
 ### `field.id.zero`
 
-This check reports an error if a field's ID is zero, which is generally
-unsupported by the Apache Thrift compiler. This is distinct from the
-`field.id.negative` check given the existence of the `--allow-neg-keys`
+This check reports an error if a field's ID is explicitly zero, which is
+generally unsupported by the Apache Thrift compiler. This is distinct from
+the `field.id.negative` check given the existence of the `--allow-neg-keys`
 Apache Thrift compiler option.
 
 ### `field.optional`

checks/fields.go

@@ -28,19 +28,19 @@ func CheckFieldIDMissing() *thriftcheck.Check {
 	})
 }
 
-// CheckFieldIDNegative reports an error if a field's ID is negative.
+// CheckFieldIDNegative reports an error if a field's ID is explicitly negative.
 func CheckFieldIDNegative() *thriftcheck.Check {
 	return thriftcheck.NewCheck("field.id.negative", func(c *thriftcheck.C, f *ast.Field) {
-		if f.ID < 0 {
+		if !f.IDUnset && f.ID < 0 {
 			c.Errorf(f, "field ID for %q (%d) is negative", f.Name, f.ID)
 		}
 	})
 }
 
-// CheckFieldIDZero reports an error if a field's ID is zero.
+// CheckFieldIDZero reports an error if a field's ID is explicitly zero.
 func CheckFieldIDZero() *thriftcheck.Check {
 	return thriftcheck.NewCheck("field.id.zero", func(c *thriftcheck.C, f *ast.Field) {
-		if f.ID == 0 {
+		if !f.IDUnset && f.ID == 0 {
 			c.Errorf(f, "field ID for %q is zero", f.Name)
 		}
 	})

checks/fields_test.go

@@ -55,6 +55,10 @@ func TestCheckFieldIDNegative(t *testing.T) {
 				`t.thrift:0:1: error: field ID for "Field" (-1) is negative (field.id.negative)`,
 			},
 		},
+		{
+			node: &ast.Field{IDUnset: true},
+			want: []string{},
+		},
 	}
 
 	check := checks.CheckFieldIDNegative()
@@ -77,6 +81,10 @@ func TestCheckFieldIDZero(t *testing.T) {
 			node: &ast.Field{ID: -1, Name: "Field"},
 			want: []string{},
 		},
+		{
+			node: &ast.Field{IDUnset: true},
+			want: []string{},
+		},
 	}
 
 	check := checks.CheckFieldIDZero()