[#928] Impl producing compiler error when required return is missing

Cesium.CodeGen.Tests/CodeGenDeclarationsTests.cs

@@ -26,6 +26,7 @@ public Task StaticDeclarationsInDifferentFunctions() => DoTest(
 int test()
 {
     static int i = 2;
+    return 0;
 }");
 
     [Fact]

Cesium.CodeGen.Tests/CodeGenMethodTests.cs

@@ -346,11 +346,24 @@ public Task ImplicitReturnAllowedForMain() => DoTest(@"int main()
     int unused = 0;
 }");
 
-    [Fact]
-    public void ImplicitReturnAllowedNonMain() => DoTest(@"int foo()
+    [Fact, NoVerify]
+    public void ImplicitReturnNotAllowedNonMain() => DoesNotCompile(@"int foo()
 {
     int unused;
-}");
+}", "Not all control flow paths in function foo return a value.");
+
+    [Fact, NoVerify]
+    public void ReturnIsNecessaryOnEntirePathsForNonMain() => DoesNotCompile(@"int foo()
+{
+    if(1)
+    {
+        // missed return
+    }
+    else
+    {
+        return 1;
+    }
+}", "Not all control flow paths in function foo return a value.");
 
     [Fact, NoVerify]
     public void ExpressionReturnDisallowedInVoidFunction() => DoesNotCompile(@"void foo()

Cesium.CodeGen.Tests/CodeGenSwitchTests.cs

@@ -141,7 +141,7 @@ public Task LowerExpression() => DoTest(@"
 int my_condition() { return 0; }
 int main()
 {
-    switch(my_condition()) { 
+    switch(my_condition()) {
         case 0: break;
         case 1:
         default: break;

Cesium.CodeGen.Tests/CodeGenWhileTests.cs

@@ -32,4 +32,36 @@ public Task DoWhile() => DoTest(
     int i = 0;
     do ++i; while (i < 10);
 }");
+
+    [Fact]
+    public Task InfinityWhile() => DoTest(
+        @"int main()
+{
+    int i = 0;
+    while (1) i++;
+}");
+
+    [Fact]
+    public Task InfinityDoWhile() => DoTest(
+        @"int main()
+{
+    int i = 0;
+    do i++; while (1);
+}");
+
+    [Fact]
+    public Task NegativeWhile() => DoTest(
+        @"int main()
+{
+    int i = 0;
+    while (!1) i++;
+}");
+
+    [Fact]
+    public Task NegativeDoWhile() => DoTest(
+        @"int main()
+{
+    int i = 0;
+    do i++; while (!1);
+}");
 }