From e78e786c14cd99fe5de2ba86dadf1fa6861384c0 Mon Sep 17 00:00:00 2001
From: James Harris <contact@jamesharris.id.au>
Date: Thu, 11 Jul 2024 14:28:58 +1000
Subject: [PATCH] Add required `default` case to generated `Map_XXX()` and
 `Switch_XXX()` functions for one-of fields.

---
 CHANGELOG.md                                 |   8 +
 go.mod                                       |   2 +-
 internal/generator/exhaustiveswitch/oneof.go |  47 ++---
 internal/test/exhaustiveswitch/oneof_test.go | 173 ++++++++-----------
 4 files changed, 107 insertions(+), 123 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index b33240b..6f37459 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,13 @@ The format is based on [Keep a Changelog], and this project adheres to
 [Keep a Changelog]: https://keepachangelog.com/en/1.0.0/
 [Semantic Versioning]: https://semver.org/spec/v2.0.0.html
 
+## [0.3.0] - 2024-07-11
+
+### Changed
+
+- **[BC]** Added a mandatory `default_` parameter to the `Map_XXX()` and
+  `Switch_XXX()` functions generated for one-of fields.
+
 ## [0.2.4] - 2024-07-11
 
 ### Fixed
@@ -105,6 +112,7 @@ The format is based on [Keep a Changelog], and this project adheres to
 [0.2.2]: https://github.com/dogmatiq/primo/releases/tag/v0.2.2
 [0.2.3]: https://github.com/dogmatiq/primo/releases/tag/v0.2.3
 [0.2.4]: https://github.com/dogmatiq/primo/releases/tag/v0.2.4
+[0.3.0]: https://github.com/dogmatiq/primo/releases/tag/v0.3.0
 
 <!-- version template
 ## [0.0.1] - YYYY-MM-DD
diff --git a/go.mod b/go.mod
index 689375c..c22962d 100644
--- a/go.mod
+++ b/go.mod
@@ -1,6 +1,6 @@
 module github.com/dogmatiq/primo
 
-go 1.21
+go 1.22
 
 require (
 	github.com/dave/jennifer v1.7.0
diff --git a/internal/generator/exhaustiveswitch/oneof.go b/internal/generator/exhaustiveswitch/oneof.go
index a2e3a5a..e60ddcc 100644
--- a/internal/generator/exhaustiveswitch/oneof.go
+++ b/internal/generator/exhaustiveswitch/oneof.go
@@ -1,8 +1,6 @@
 package exhaustiveswitch
 
 import (
-	"fmt"
-
 	"github.com/dave/jennifer/jen"
 	"github.com/dogmatiq/primo/internal/generator/internal/scope"
 )
@@ -31,7 +29,7 @@ func generateOneOfSwitch(code *jen.File, g *scope.OneOfGroup) {
 		)
 	code.Comment("")
 	code.Commentf(
-		"It panics if x.%s is nil.",
+		"It calls the function associated with the default case if x.%s is nil.",
 		g.GoFieldName,
 	)
 
@@ -56,6 +54,12 @@ func generateOneOfSwitch(code *jen.File, g *scope.OneOfGroup) {
 						)
 				}
 
+				code.
+					Line().
+					Id("default_").
+					Func().
+					Params()
+
 				code.Line()
 			},
 		).
@@ -90,15 +94,8 @@ func generateOneOfSwitch(code *jen.File, g *scope.OneOfGroup) {
 
 						code.
 							Default().
-							Panic(
-								jen.Lit(
-									fmt.Sprintf(
-										"%s: x.%s is nil",
-										funcName,
-										g.GoFieldName,
-									),
-								),
-							)
+							Id("default_").
+							Call()
 					},
 				),
 		)
@@ -119,8 +116,11 @@ func generateOneOfMap(code *jen.File, g *scope.OneOfGroup) {
 		"It invokes the function that corresponds to the value of x.%s,",
 		g.GoFieldName,
 	)
+	code.Comment(
+		"and returns that function's result. It calls the function associated with",
+	)
 	code.Commentf(
-		"and returns that function's result. It panics if x.%s is nil.",
+		"the default case if x.%s is nil.",
 		g.GoFieldName,
 	)
 
@@ -151,6 +151,15 @@ func generateOneOfMap(code *jen.File, g *scope.OneOfGroup) {
 						)
 				}
 
+				code.
+					Line().
+					Id("default_").
+					Func().
+					Params().
+					Params(
+						jen.Id("T"),
+					)
+
 				code.Line()
 			},
 		).
@@ -189,15 +198,9 @@ func generateOneOfMap(code *jen.File, g *scope.OneOfGroup) {
 
 						code.
 							Default().
-							Panic(
-								jen.Lit(
-									fmt.Sprintf(
-										"%s: x.%s is nil",
-										funcName,
-										g.GoFieldName,
-									),
-								),
-							)
+							Return().
+							Id("default_").
+							Call()
 					},
 				),
 		)
diff --git a/internal/test/exhaustiveswitch/oneof_test.go b/internal/test/exhaustiveswitch/oneof_test.go
index 21e65c9..a9e3d98 100644
--- a/internal/test/exhaustiveswitch/oneof_test.go
+++ b/internal/test/exhaustiveswitch/oneof_test.go
@@ -28,6 +28,7 @@ func TestOneOfSwitch(t *testing.T) {
 				func(v int32) { called = true },
 				func(m string) { panic("unexpected log operation") },
 				func(*Record_NamingCollision) { panic("unexpected NamingCollision operation") },
+				func() { panic("unexpected default case") },
 			)
 
 			if !called {
@@ -37,60 +38,46 @@ func TestOneOfSwitch(t *testing.T) {
 	)
 
 	t.Run(
-		"it panics if the field is nil",
+		"it calls the function associated with the default case if the one-of field is nil",
 		func(t *testing.T) {
 			t.Parallel()
 
-			rec := &Record{}
-
-			defer func() {
-				got := recover()
-				want := "Switch_Record_Operation: x.Operation is nil"
-
-				if got != want {
-					t.Fatalf(
-						"unexpected panic message: got %q, want %q",
-						got,
-						want,
-					)
-				}
-			}()
-
-			Switch_Record_Operation(
-				rec,
-				func(int32) { panic("unexpected increment operation") },
-				func(int32) { panic("unexpected decrement operation") },
-				func(string) { panic("unexpected log operation") },
-				func(*Record_NamingCollision) { panic("unexpected NamingCollision operation") },
-			)
-		},
-	)
-
-	t.Run(
-		"it panics if the message is nil",
-		func(t *testing.T) {
-			t.Parallel()
-
-			defer func() {
-				got := recover()
-				want := "Switch_Record_Operation: x.Operation is nil"
-
-				if got != want {
-					t.Fatalf(
-						"unexpected panic message: got %q, want %q",
-						got,
-						want,
-					)
-				}
-			}()
+			cases := []struct {
+				name   string
+				record *Record
+			}{
+				{
+					"nil message",
+					nil,
+				},
+				{
+					"nil field",
+					&Record{},
+				},
+			}
 
-			Switch_Record_Operation(
-				nil,
-				func(int32) { panic("unexpected increment operation") },
-				func(int32) { panic("unexpected decrement operation") },
-				func(string) { panic("unexpected log operation") },
-				func(*Record_NamingCollision) { panic("unexpected NamingCollision operation") },
-			)
+			for _, c := range cases {
+				t.Run(
+					c.name,
+					func(t *testing.T) {
+						t.Parallel()
+
+						called := false
+
+						Switch_Record_Operation(
+							c.record,
+							func(int32) { panic("unexpected increment operation") },
+							func(int32) { panic("unexpected decrement operation") },
+							func(string) { panic("unexpected log operation") },
+							func(*Record_NamingCollision) { panic("unexpected NamingCollision operation") },
+							func() { called = true },
+						)
+
+						if !called {
+							t.Fatalf("expected case function to be called")
+						}
+					})
+			}
 		},
 	)
 }
@@ -116,6 +103,7 @@ func TestOneOfMap(t *testing.T) {
 				func(v int32) int32 { return v - 1 },
 				func(m string) int32 { panic("unexpected log operation") },
 				func(*Record_NamingCollision) int32 { panic("unexpected NamingCollision operation") },
+				func() int32 { panic("unexpected default case") },
 			)
 
 			if got != want {
@@ -125,60 +113,45 @@ func TestOneOfMap(t *testing.T) {
 	)
 
 	t.Run(
-		"it panics if the field is nil",
+		"it calls the function associated with the default case if the one-of field is nil",
 		func(t *testing.T) {
 			t.Parallel()
 
-			rec := &Record{}
-
-			defer func() {
-				got := recover()
-				want := "Map_Record_Operation: x.Operation is nil"
-
-				if got != want {
-					t.Fatalf(
-						"unexpected panic message: got %q, want %q",
-						got,
-						want,
-					)
-				}
-			}()
-
-			Map_Record_Operation(
-				rec,
-				func(int32) error { panic("unexpected increment operation") },
-				func(int32) error { panic("unexpected decrement operation") },
-				func(string) error { panic("unexpected log operation") },
-				func(*Record_NamingCollision) error { panic("unexpected NamingCollision operation") },
-			)
-		},
-	)
-
-	t.Run(
-		"it panics if the message is nil",
-		func(t *testing.T) {
-			t.Parallel()
+			cases := []struct {
+				name   string
+				record *Record
+			}{
+				{
+					"nil message",
+					nil,
+				},
+				{
+					"nil field",
+					&Record{},
+				},
+			}
 
-			defer func() {
-				got := recover()
-				want := "Map_Record_Operation: x.Operation is nil"
-
-				if got != want {
-					t.Fatalf(
-						"unexpected panic message: got %q, want %q",
-						got,
-						want,
-					)
-				}
-			}()
-
-			Map_Record_Operation(
-				nil,
-				func(int32) error { panic("unexpected increment operation") },
-				func(int32) error { panic("unexpected decrement operation") },
-				func(string) error { panic("unexpected log operation") },
-				func(*Record_NamingCollision) error { panic("unexpected NamingCollision operation") },
-			)
+			for _, c := range cases {
+				t.Run(
+					c.name,
+					func(t *testing.T) {
+						t.Parallel()
+
+						want := int32(123)
+						got := Map_Record_Operation(
+							c.record,
+							func(int32) int32 { panic("unexpected increment operation") },
+							func(int32) int32 { panic("unexpected decrement operation") },
+							func(string) int32 { panic("unexpected log operation") },
+							func(*Record_NamingCollision) int32 { panic("unexpected NamingCollision operation") },
+							func() int32 { return 123 },
+						)
+
+						if got != want {
+							t.Fatalf("unexpected result: got %q, want %q", got, want)
+						}
+					})
+			}
 		},
 	)
 }