Make loplugin:unnecessaryparen look through implicit

...similar to how <https://gerrit.libreoffice.org/#/c/45083/2> "Make not warning
about !! in loplugin:simplifybool consistent" does for loplugin:simplifybool

Change-Id: I23eef400af71c582d380c9bae6546ce06e8a1e18
Reviewed-on: https://gerrit.libreoffice.org/45122
Tested-by: Stephan Bergmann <sbergman@redhat.com>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

2 files changed, 28 insertions, 3 deletions

diff --git a/compilerplugins/clang/test/unnecessaryparen.cxx b/compilerplugins/clang/test/unnecessaryparen.cxx
index 968522d63a73..4e85fe97076f 100644
--- a/compilerplugins/clang/test/unnecessaryparen.cxx
+++ b/compilerplugins/clang/test/unnecessaryparen.cxx
@@ -14,6 +14,8 @@ bool foo(int);
 
 enum class EFoo { Bar };
 
+struct S { operator bool(); };
+
 int main()
 {
     int x = 1;
@@ -49,6 +51,16 @@ int main()
     std::string v3;
     v3 = (std::string("xx") + "xx"); // expected-error {{parentheses immediately inside assignment [loplugin:unnecessaryparen]}}
     (void)v3;
+
+    S s1;
+    if ((s1)) { // expected-error {{parentheses immediately inside if statement [loplugin:unnecessaryparen]}}
+        // expected-error@-1 {{unnecessary parentheses around identifier [loplugin:unnecessaryparen]}}
+        return 0;
+    }
+    S s2;
+    if ((s2 = s1)) {
+        return 0;
+    }
 };
 
 /* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */
diff --git a/compilerplugins/clang/unnecessaryparen.cxx b/compilerplugins/clang/unnecessaryparen.cxx
index fdc83410cb0e..a7d3d26e6591 100644
--- a/compilerplugins/clang/unnecessaryparen.cxx
+++ b/compilerplugins/clang/unnecessaryparen.cxx
@@ -23,8 +23,8 @@ look for unnecessary parentheses
 
 namespace {
 
-// Like clang::Stmt::IgnoreImplicit (lib/AST/Stmt.cpp), but also ignoring
-// CXXConstructExpr:
+// Like clang::Stmt::IgnoreImplicit (lib/AST/Stmt.cpp), but also ignoring CXXConstructExpr and
+// looking through implicit UserDefinedConversion's member function call:
 Expr const * ignoreAllImplicit(Expr const * expr) {
     if (auto const e = dyn_cast<ExprWithCleanups>(expr)) {
         expr = e->getSubExpr();
@@ -40,7 +40,15 @@ Expr const * ignoreAllImplicit(Expr const * expr) {
     if (auto const e = dyn_cast<CXXBindTemporaryExpr>(expr)) {
         expr = e->getSubExpr();
     }
-    return expr->IgnoreImpCasts();
+    while (auto const e = dyn_cast<ImplicitCastExpr>(expr)) {
+        expr = e->getSubExpr();
+        if (e->getCastKind() == CK_UserDefinedConversion) {
+            auto const ce = cast<CXXMemberCallExpr>(expr);
+            assert(ce->getNumArgs() == 0);
+            expr = ce->getImplicitObjectArgument();
+        }
+    }
+    return expr;
 }
 
 class UnnecessaryParen:
@@ -239,6 +247,11 @@ void UnnecessaryParen::VisitSomeStmt(const Stmt * stmt, const Expr* cond, String
         auto binaryOp = dyn_cast<BinaryOperator>(parenExpr->getSubExpr());
         if (binaryOp && binaryOp->getOpcode() == BO_Assign)
             return;
+        if (auto const opCall = dyn_cast<CXXOperatorCallExpr>(parenExpr->getSubExpr())) {
+            if (opCall->getOperator() == OO_Equal) {
+                return;
+            }
+        }
         report(
             DiagnosticsEngine::Warning, "parentheses immediately inside %0 statement",
             parenExpr->getLocStart())