From a4456d8ecfa5d4f4e8756b983465c58068b8a561 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Stanis=C5=82aw=20Barzowski?= <sbarzowski@google.com>
Date: Fri, 18 Aug 2017 14:16:05 -0400
Subject: [PATCH] Add desugaring of standalone assertions

---
 desugarer.go                         | 17 +++++++++++++++--
 testdata/assert.golden               |  1 +
 testdata/assert.input                |  1 +
 testdata/assert_failed.golden        |  1 +
 testdata/assert_failed.input         |  1 +
 testdata/assert_failed_custom.golden |  1 +
 testdata/assert_failed_custom.input  |  1 +
 7 files changed, 21 insertions(+), 2 deletions(-)
 create mode 100644 testdata/assert.golden
 create mode 100644 testdata/assert.input
 create mode 100644 testdata/assert_failed.golden
 create mode 100644 testdata/assert_failed.input
 create mode 100644 testdata/assert_failed_custom.golden
 create mode 100644 testdata/assert_failed_custom.input

diff --git a/desugarer.go b/desugarer.go
index d5c6f04..5e68688 100644
--- a/desugarer.go
+++ b/desugarer.go
@@ -228,6 +228,13 @@ func desugarObjectComp(astComp *ast.ObjectComp, objLevel int) (ast.Node, error)
 	// TODO(sbarzowski) this
 }
 
+func buildLiteralString(value string) ast.Node {
+	return &ast.LiteralString{
+		Kind:  ast.StringDouble,
+		Value: value,
+	}
+}
+
 func buildSimpleIndex(obj ast.Node, member ast.Identifier) ast.Node {
 	return &ast.Index{
 		Target: obj,
@@ -301,8 +308,14 @@ func desugar(astPtr *ast.Node, objLevel int) (err error) {
 		*astPtr = comp
 
 	case *ast.Assert:
-		// TODO(sbarzowski) this
-		*astPtr = &ast.LiteralNull{}
+		if node.Message == nil {
+			node.Message = buildLiteralString("Assertion failed")
+		}
+		*astPtr = &ast.Conditional{
+			Cond:        node.Cond,
+			BranchTrue:  node.Rest,
+			BranchFalse: &ast.Error{Expr: node.Message},
+		}
 
 	case *ast.Binary:
 		// some operators get replaced by stdlib functions
diff --git a/testdata/assert.golden b/testdata/assert.golden
new file mode 100644
index 0000000..27ba77d
--- /dev/null
+++ b/testdata/assert.golden
@@ -0,0 +1 @@
+true
diff --git a/testdata/assert.input b/testdata/assert.input
new file mode 100644
index 0000000..2fff0f6
--- /dev/null
+++ b/testdata/assert.input
@@ -0,0 +1 @@
+assert true; true
diff --git a/testdata/assert_failed.golden b/testdata/assert_failed.golden
new file mode 100644
index 0000000..57b9b74
--- /dev/null
+++ b/testdata/assert_failed.golden
@@ -0,0 +1 @@
+RUNTIME ERROR: Assertion failed
diff --git a/testdata/assert_failed.input b/testdata/assert_failed.input
new file mode 100644
index 0000000..222c9e7
--- /dev/null
+++ b/testdata/assert_failed.input
@@ -0,0 +1 @@
+assert false; true
diff --git a/testdata/assert_failed_custom.golden b/testdata/assert_failed_custom.golden
new file mode 100644
index 0000000..6755f2a
--- /dev/null
+++ b/testdata/assert_failed_custom.golden
@@ -0,0 +1 @@
+RUNTIME ERROR: Custom Message
diff --git a/testdata/assert_failed_custom.input b/testdata/assert_failed_custom.input
new file mode 100644
index 0000000..20572db
--- /dev/null
+++ b/testdata/assert_failed_custom.input
@@ -0,0 +1 @@
+assert false : "Custom Message"; true