From 2b63997c2c55339745e8e5d89db6a6d928f9a73b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Marjam=C3=A4ki?= <daniel.marjamaki@gmail.com>
Date: Wed, 2 Jan 2019 20:23:02 +0100
Subject: [PATCH] Fixed #8928 (false positive: (style) Variable 'x' is assigned
 a value that is never used.)

---
 lib/astutils.cpp       |  7 +++++--
 lib/valueflow.cpp      |  2 +-
 test/testunusedvar.cpp | 10 ++++++++++
 3 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/lib/astutils.cpp b/lib/astutils.cpp
index 88c28338b..df48c5fac 100644
--- a/lib/astutils.cpp
+++ b/lib/astutils.cpp
@@ -1178,7 +1178,7 @@ struct FwdAnalysis::Result FwdAnalysis::checkRecursive(const Token *expr, const
             const Token *parent = tok;
             bool other = false;
             bool same = tok->astParent() && isSameExpression(mCpp, false, expr, tok, mLibrary, false, false, nullptr);
-            while (Token::Match(parent->astParent(), "*|.|::|[")) {
+            while (!same && Token::Match(parent->astParent(), "*|.|::|[")) {
                 parent = parent->astParent();
                 if (parent && isSameExpression(mCpp, false, expr, parent, mLibrary, false, false, nullptr)) {
                     same = true;
@@ -1189,11 +1189,14 @@ struct FwdAnalysis::Result FwdAnalysis::checkRecursive(const Token *expr, const
                         mValueFlow.push_back(v);
                     }
                 }
-                if (!same && Token::Match(parent, ". %var%") && parent->next()->varId() && exprVarIds.find(parent->next()->varId()) == exprVarIds.end()) {
+                if (Token::Match(parent, ". %var%") && parent->next()->varId() && exprVarIds.find(parent->next()->varId()) == exprVarIds.end()) {
                     other = true;
                     break;
                 }
             }
+            if (mWhat != What::ValueFlow && same && Token::simpleMatch(parent->astParent(), "[") && parent == parent->astParent()->astOperand2()) {
+                return Result(Result::Type::READ);
+            }
             if (other)
                 continue;
             if (Token::simpleMatch(parent->astParent(), "=") && parent == parent->astParent()->astOperand1()) {
diff --git a/lib/valueflow.cpp b/lib/valueflow.cpp
index 3efa7e645..940e8bb83 100644
--- a/lib/valueflow.cpp
+++ b/lib/valueflow.cpp
@@ -1019,7 +1019,7 @@ static void valueFlowArray(TokenList *tokenlist)
                 !tok->variable()->isStlType()) {
                 ValueFlow::Value value{1};
                 value.setKnown();
-                // TODO : this leads to too many false positives so it is commented out.  
+                // TODO : this leads to too many false positives so it is commented out.
                 // See for instance https://github.com/danmar/cppcheck/commit/025881cf35fdde1299d16a09059e7305f8c9bd13
                 // setTokenValue(tok, value, tokenlist->getSettings());
             }
diff --git a/test/testunusedvar.cpp b/test/testunusedvar.cpp
index aa07afe68..f1b7f0d43 100644
--- a/test/testunusedvar.cpp
+++ b/test/testunusedvar.cpp
@@ -109,6 +109,7 @@ private:
         TEST_CASE(localvar53); // continue
         TEST_CASE(localvar54); // ast, {}
         TEST_CASE(localvar55);
+        TEST_CASE(localvar56);
         TEST_CASE(localvarloops); // loops
         TEST_CASE(localvaralias1);
         TEST_CASE(localvaralias2); // ticket #1637
@@ -2143,6 +2144,15 @@ private:
                       errout.str());
     }
 
+    void localvar56() {
+        functionVariableUsage("void f()\n"
+                              "{\n"
+                              "    int x = 31;\n"
+                              "    mask[x] |= 123;\n"
+                              "}");
+        ASSERT_EQUALS("", errout.str());
+    }
+
     void localvarloops() {
         // loops
         functionVariableUsage("void fun() {\n"