Add MustProcess which panics on errors (#115)

* MustProcess: panic if processing fails, return the value

Signed-off-by: Jason Hall <[email protected]>

* Add MustProcess that panics if processing fails

---------

Signed-off-by: Jason Hall <[email protected]>
Co-authored-by: Jason Hall <[email protected]>

envconfig.go

@@ -285,6 +285,24 @@ func Process(ctx context.Context, i any, mus ...Mutator) error {
 	})
 }
 
+// MustProcess is a helper that calls [Process] and panics if an error is
+// encountered. Unlike [Process], the input value is returned, making it ideal
+// for anonymous initializations:
+//
+//	var env = envconfig.MustProcess(context.Background(), &struct{
+//	  Field string `env:"FIELD,required"`
+//	})
+//
+// This is not recommend for production services, but it can be useful for quick
+// CLIs and scripts that want to take advantage of envconfig's environment
+// parsing at the expense of testability and graceful error handling.
+func MustProcess[T any](ctx context.Context, i T, mus ...Mutator) T {
+	if err := Process(ctx, i, mus...); err != nil {
+		panic(err)
+	}
+	return i
+}
+
 // ProcessWith executes the decoding process using the provided [Config].
 func ProcessWith(ctx context.Context, c *Config) error {
 	if c == nil {

envconfig_test.go

@@ -2958,6 +2958,71 @@ func TestProcessWith(t *testing.T) {
 	}
 }
 
+func TestMustProcess(t *testing.T) {
+	cases := []struct {
+		name     string
+		target   any
+		exp      any
+		env      map[string]string
+		expPanic bool
+	}{
+		{
+			name: "panics_on_error",
+			target: &struct {
+				Field string `env:"FIELD,required"`
+			}{},
+			exp: &struct {
+				Field string `env:"FIELD,required"`
+			}{},
+			env:      nil,
+			expPanic: true,
+		},
+		{
+			name: "returns_value",
+			target: &struct {
+				Field string `env:"FIELD,required"`
+			}{},
+			exp: &struct {
+				Field string `env:"FIELD,required"`
+			}{
+				Field: "value",
+			},
+			env: map[string]string{
+				"FIELD": "value",
+			},
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			for k, v := range tc.env {
+				t.Setenv(k, v)
+			}
+
+			defer func() {
+				if r := recover(); r != nil {
+					if !tc.expPanic {
+						t.Fatal(r)
+					}
+				} else if tc.expPanic {
+					t.Errorf("expected a panic")
+				}
+			}()
+
+			ctx := context.Background()
+			got := MustProcess(ctx, tc.target)
+
+			if got != tc.target {
+				t.Errorf("expected result to be the same object as target (%#v, %#v)", got, tc.target)
+			}
+
+			if diff := cmp.Diff(tc.exp, tc.target); diff != "" {
+				t.Fatalf("mismatch (-want, +got):\n%s", diff)
+			}
+		})
+	}
+}
+
 func TestValidateEnvName(t *testing.T) {
 	t.Parallel()