Fix assertions due to malformed switch statements (#3858)

* Fix assertions due to malformed switch statements

Fixes the issue #2955

* Checks for multiple case statements with same values
* Checks for multiple default cases
* Constant-folds case exprs into an Integer value

* fix the comments, and updated error code

* one-line comment on diagnostic code

2 files changed, 47 insertions, 0 deletions

diff --git a/tests/diagnostics/switch-duplicate-case.slang b/tests/diagnostics/switch-duplicate-case.slang
new file mode 100644
index 000000000..2d55dc4c8
--- /dev/null
+++ b/tests/diagnostics/switch-duplicate-case.slang
@@ -0,0 +1,33 @@
+//TEST:SIMPLE(filecheck=CHECK):
+
+// Tests to evaluate the behavior of code blocks within a switch statement. A switch statement with duplicate cases with same values is not allowed and should throw an error
+
+enum class Cases
+{
+    A,
+    B
+};
+
+void test1(Cases c)
+{
+    switch (c)
+    {
+        case Cases::A: break;
+        case Cases::B: break;
+        // CHECK: ([[# @LINE+1]]): error 30601: {{.*}}
+        case Cases::A: break;
+    }
+    return;
+}
+
+void test2()
+{
+    switch (0)
+    {
+        case 1: break;
+        case 2: break;
+        // CHECK: ([[# @LINE+1]]): error 30601: {{.*}}
+        case 1: break;
+    }
+	return;
+}
diff --git a/tests/diagnostics/switch-multiple-defaults.slang b/tests/diagnostics/switch-multiple-defaults.slang
new file mode 100644
index 000000000..bf164dd57
--- /dev/null
+++ b/tests/diagnostics/switch-multiple-defaults.slang
@@ -0,0 +1,14 @@
+//TEST:SIMPLE(filecheck=CHECK):
+
+// Test to evaluate the behavior of unreachable code blocks within a switch statement. A switch statement with multiple default cases is not allowed and should throw an error
+
+void test()
+{
+    switch (0)
+    {
+        default: break;
+        // CHECK: ([[# @LINE+1]]): error 30600: {{.*}}
+        default: break;
+    }
+	return;
+}