New loplugin:empty

Change-Id: I8729db064573ac21dfe6b203c5ae244d79ecc4fe
Reviewed-on: https://gerrit.libreoffice.org/66430
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

1 files changed, 186 insertions, 0 deletions

diff --git a/compilerplugins/clang/empty.cxx b/compilerplugins/clang/empty.cxx
new file mode 100644
index 000000000000..74cc7b06e176
--- /dev/null
+++ b/compilerplugins/clang/empty.cxx
@@ -0,0 +1,186 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4; fill-column: 100 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+#include <cassert>
+
+#include "check.hxx"
+#include "plugin.hxx"
+
+// Warn about checks whether a container is empty done via an (expensive) call to obtain the
+// container's size.  For now only handles cases involving strlen.
+
+namespace
+{
+BinaryOperatorKind revert(BinaryOperatorKind op)
+{
+    switch (op)
+    {
+        case BO_LT:
+            return BO_GE;
+        case BO_GT:
+            return BO_LE;
+        case BO_LE:
+            return BO_GT;
+        case BO_GE:
+            return BO_LT;
+        case BO_EQ:
+        case BO_NE:
+            return op;
+        default:
+            assert(false);
+    }
+}
+
+class Empty : public loplugin::FilteringPlugin<Empty>
+{
+public:
+    explicit Empty(loplugin::InstantiationData const& data)
+        : FilteringPlugin(data)
+    {
+    }
+
+    bool VisitBinLT(BinaryOperator const* expr)
+    {
+        visitComparison(expr);
+        return true;
+    }
+
+    bool VisitBinGT(BinaryOperator const* expr)
+    {
+        visitComparison(expr);
+        return true;
+    }
+
+    bool VisitBinLE(BinaryOperator const* expr)
+    {
+        visitComparison(expr);
+        return true;
+    }
+
+    bool VisitBinGE(BinaryOperator const* expr)
+    {
+        visitComparison(expr);
+        return true;
+    }
+
+    bool VisitBinEQ(BinaryOperator const* expr)
+    {
+        visitComparison(expr);
+        return true;
+    }
+
+    bool VisitBinNE(BinaryOperator const* expr)
+    {
+        visitComparison(expr);
+        return true;
+    }
+
+private:
+    void run() override { TraverseDecl(compiler.getASTContext().getTranslationUnitDecl()); }
+
+    void visitComparison(BinaryOperator const* expr, CallExpr const* lhs, Expr const* rhs,
+                         BinaryOperatorKind op)
+    {
+        auto const fdecl = lhs->getDirectCallee();
+        if (fdecl == nullptr)
+        {
+            return;
+        }
+        loplugin::DeclCheck dc(fdecl);
+        if (!(dc.Function("strlen").StdNamespace() || dc.Function("strlen").GlobalNamespace()))
+        {
+            return;
+        }
+        APSInt val;
+        if (!rhs->isIntegerConstantExpr(val, compiler.getASTContext()))
+        {
+            return;
+        }
+        switch (op)
+        {
+            case BO_LT:
+                if (val.getExtValue() == 1)
+                {
+                    report(DiagnosticsEngine::Warning,
+                           "replace a comparison like 'strlen(e) < 1' with 'e[0] == '\\0''",
+                           expr->getExprLoc())
+                        << expr->getSourceRange();
+                }
+                break;
+            case BO_GT:
+                if (val.getExtValue() == 0)
+                {
+                    report(DiagnosticsEngine::Warning,
+                           "replace a comparison like 'strlen(e) > 0' with 'e[0] != '\\0''",
+                           expr->getExprLoc())
+                        << expr->getSourceRange();
+                }
+                break;
+            case BO_LE:
+                if (val.getExtValue() == 0)
+                {
+                    report(DiagnosticsEngine::Warning,
+                           "replace a comparison like 'strlen(e) <= 0' with 'e[0] == '\\0''",
+                           expr->getExprLoc())
+                        << expr->getSourceRange();
+                }
+                break;
+            case BO_GE:
+                if (val.getExtValue() == 1)
+                {
+                    report(DiagnosticsEngine::Warning,
+                           "replace a comparison like 'strlen(e) >= 1' with 'e[0] != '\\0''",
+                           expr->getExprLoc())
+                        << expr->getSourceRange();
+                }
+                break;
+            case BO_EQ:
+                if (val.getExtValue() == 0)
+                {
+                    report(DiagnosticsEngine::Warning,
+                           "replace a comparison like 'strlen(e) == 0' with 'e[0] == '\\0''",
+                           expr->getExprLoc())
+                        << expr->getSourceRange();
+                }
+                break;
+            case BO_NE:
+                if (val.getExtValue() == 0)
+                {
+                    report(DiagnosticsEngine::Warning,
+                           "replace a comparison like 'strlen(e) != 0' with 'e[0] != '\\0''",
+                           expr->getExprLoc())
+                        << expr->getSourceRange();
+                }
+                break;
+            default:
+                assert(false);
+        }
+    }
+
+    void visitComparison(BinaryOperator const* expr)
+    {
+        if (ignoreLocation(expr))
+        {
+            return;
+        }
+        if (auto const call = dyn_cast<CallExpr>(expr->getLHS()->IgnoreParenImpCasts()))
+        {
+            visitComparison(expr, call, expr->getRHS(), expr->getOpcode());
+        }
+        else if (auto const call = dyn_cast<CallExpr>(expr->getRHS()->IgnoreParenImpCasts()))
+        {
+            visitComparison(expr, call, expr->getLHS(), revert(expr->getOpcode()));
+        }
+    }
+};
+
+loplugin::Plugin::Registration<Empty> X("empty");
+}
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */