Add expression functions with context boundaries

internal/lang/expression_function_test.go

@@ -0,0 +1,86 @@
+package lang
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestExpressionBodiedFunctionInfersReturnType(t *testing.T) {
+	program, err := Parse(`package demo
+fun twice(value: Int) = value * 2
+fun text() = "value"`)
+	if err != nil {
+		t.Fatal(err)
+	}
+	output, err := GenerateGo(program)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, expected := range []string{"func twice(value int) int", "return value * 2", "func text() string", `return "value"`} {
+		if !strings.Contains(string(output), expected) {
+			t.Fatalf("missing %q:\n%s", expected, output)
+		}
+	}
+	if got := ResolvedType(program.Functions[0].ExpressionBody).String(); got != "Int" {
+		t.Fatalf("return type = %s", got)
+	}
+}
+
+func TestExpressionBodyInferenceReachesFixedPoint(t *testing.T) {
+	program, err := Parse(`package demo
+fun first() = second()
+fun second() = third()
+fun third() = 42`)
+	if err != nil {
+		t.Fatal(err)
+	}
+	semantic, err := Analyze(program)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, name := range []string{"first", "second", "third"} {
+		symbol, _ := semantic.Global.Lookup(name)
+		if got := symbol.Type.(FunctionType).Result.String(); got != "Int" {
+			t.Fatalf("%s result = %s", name, got)
+		}
+	}
+}
+
+func TestWithContextExpressionBodyEstablishesBoundary(t *testing.T) {
+	program, err := Parse(`package demo
+import http net.http
+import exec os.exec
+fun work() { exec.commandContext("date") }
+fun handle(request: *http.Request) = withContext(request.context()) {
+    work()
+}`)
+	if err != nil {
+		t.Fatal(err)
+	}
+	semantic, err := Analyze(program)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !semantic.FunctionEffects["work"].Has(CoroutineEffect) {
+		t.Fatal("work should require ambient context")
+	}
+	if semantic.FunctionEffects["handle"].Has(CoroutineEffect) {
+		t.Fatal("withContext should be an effect boundary")
+	}
+	output, err := GenerateGo(program)
+	if err != nil {
+		t.Fatal(err)
+	}
+	code := string(output)
+	for _, expected := range []string{
+		"func work(gotlinScope *GotlinCoroutineScope)",
+		`exec.CommandContext(gotlinScope.Context(), "date")`,
+		"func handle(request *http.Request)",
+		"gotlinRunWithContext(request.Context()",
+		"work(gotlinScope)",
+	} {
+		if !strings.Contains(code, expected) {
+			t.Fatalf("missing %q:\n%s", expected, code)
+		}
+	}
+}