[-Wunsafe-buffer-usage] Initial commit - Transition away from raw buffers.

This is the initial commit for -Wunsafe-buffer-usage, a warning that helps
codebases (especially modern C++ codebases) transition away from raw buffer
pointers.

The warning is implemented in libAnalysis as it's going to become a non-trivial
analysis, mostly the fixit part where we try to figure out if we understand
a variable's use pattern well enough to suggest a safe container/view
as a replacement. Some parts of this analsysis may eventually prove useful
for any similar fixit machine that tries to change types of variables.

The warning is disabled by default.

RFC/discussion in https://discourse.llvm.org/t/rfc-c-buffer-hardening/65734

Differential Revision: https://reviews.llvm.org/D137346

1 files changed, 24 insertions, 0 deletions

diff --git a/clang/lib/Sema/AnalysisBasedWarnings.cpp b/clang/lib/Sema/AnalysisBasedWarnings.cpp
index 9780a0a..70b81c0 100644
--- a/clang/lib/Sema/AnalysisBasedWarnings.cpp
+++ b/clang/lib/Sema/AnalysisBasedWarnings.cpp
@@ -29,6 +29,7 @@
 #include "clang/Analysis/Analyses/ReachableCode.h"
 #include "clang/Analysis/Analyses/ThreadSafety.h"
 #include "clang/Analysis/Analyses/UninitializedValues.h"
+#include "clang/Analysis/Analyses/UnsafeBufferUsage.h"
 #include "clang/Analysis/AnalysisDeclContext.h"
 #include "clang/Analysis/CFG.h"
 #include "clang/Analysis/CFGStmtMap.h"
@@ -2139,6 +2140,23 @@ public:
 } // namespace clang
 
 //===----------------------------------------------------------------------===//
+// Unsafe buffer usage analysis.
+//===----------------------------------------------------------------------===//
+
+class UnsafeBufferUsageReporter : public UnsafeBufferUsageHandler {
+  Sema &S;
+
+public:
+  UnsafeBufferUsageReporter(Sema &S) : S(S) {}
+
+  void handleUnsafeOperation(const Stmt *Operation) override {
+    S.Diag(Operation->getBeginLoc(), diag::warn_unsafe_buffer_usage)
+        << Operation->getSourceRange();
+  }
+};
+
+
+//===----------------------------------------------------------------------===//
 // AnalysisBasedWarnings - Worker object used by Sema to execute analysis-based
 //  warnings on a function, method, or block.
 //===----------------------------------------------------------------------===//
@@ -2430,6 +2448,12 @@ void clang::sema::AnalysisBasedWarnings::IssueWarnings(
       if (S.getLangOpts().CPlusPlus && isNoexcept(FD))
         checkThrowInNonThrowingFunc(S, FD, AC);
 
+  // Emit unsafe buffer usage warnings and fixits.
+  if (!Diags.isIgnored(diag::warn_unsafe_buffer_usage, D->getBeginLoc())) {
+    UnsafeBufferUsageReporter R(S);
+    checkUnsafeBufferUsage(D, R);
+  }
+
   // If none of the previous checks caused a CFG build, trigger one here
   // for the logical error handler.
   if (LogicalErrorHandler::hasActiveDiagnostics(Diags, D->getBeginLoc())) {