[clang] [clang][analyzer] Add StoreToImmutable checker (PR #150417)

[Donát Nagy via cfe-commits]

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+// RUN: %clang_analyze_cc1 -analyzer-checker=alpha.core.StoreToImmutable -verify %s
+
+// Test basic functionality of StoreToImmutable checker
+// This tests direct writes to immutable regions without function modeling
+
+// Direct write to a const global variable
+const int global_const = 42; // expected-note {{Memory region is in immutable space}}
+
+void test_direct_write_to_const_global() {
+  // This should trigger a warning about writing to immutable memory
+  *(int*)&global_const = 100; // expected-warning {{Writing to immutable memory is undefined behavior}}
+  // expected-note at -1 {{Writing to immutable memory is undefined behavior. This memory region is marked as immutable and should not be modified}}
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NagyDonat wrote:

I'm also very surprised to see that `note` diagnostics are visible without `-analyzer-output=text` but I don't have a strong opinion about whether this is a problem or not.

> It may have something to do with the raw use of the addNote API, which is not usually done. We usually use BugReport visitors for putting down notes and probably their behavior is different. [...]
>
> I tried to grep for one case when we emit notes from a static analyzer checker and could not find one.

Just a quick drive-by remark: `CStringChecker::emitUninitializedReadBug` also adds a note with a direct `addNote` call instead of using a bug reporter visitor.

https://github.com/llvm/llvm-project/pull/150417