From 1d19b2d96f6e383da520c8b96306bb047828eea5 Mon Sep 17 00:00:00 2001
From: peter <peter@jetbrains.com>
Date: Wed, 22 May 2013 17:49:58 +0200
Subject: [PATCH] IDEA-106884 Detect that string concatenation produces
 not-null result

---
 .../dataFlow/ControlFlowAnalyzer.java             |  5 +++++
 .../fixture/StringConcatAlwaysNotNull.java        | 15 +++++++++++++++
 .../codeInspection/DataFlowInspectionTest.java    |  1 +
 3 files changed, 21 insertions(+)
 create mode 100644 java/java-tests/testData/inspection/dataFlow/fixture/StringConcatAlwaysNotNull.java

diff --git a/java/java-impl/src/com/intellij/codeInspection/dataFlow/ControlFlowAnalyzer.java b/java/java-impl/src/com/intellij/codeInspection/dataFlow/ControlFlowAnalyzer.java
index c3e51a45218d..229f4656634c 100644
--- a/java/java-impl/src/com/intellij/codeInspection/dataFlow/ControlFlowAnalyzer.java
+++ b/java/java-impl/src/com/intellij/codeInspection/dataFlow/ControlFlowAnalyzer.java
@@ -182,6 +182,11 @@ class ControlFlowAnalyzer extends JavaElementVisitor {
           generateDefaultBinOp(lExpr, rExpr, type);
         }
       }
+      else if (op == JavaTokenType.PLUSEQ && type != null && type.equalsToText(JAVA_LANG_STRING)) {
+        lExpr.accept(this);
+        rExpr.accept(this);
+        addInstruction(new BinopInstruction(JavaTokenType.PLUS, null, lExpr.getProject()));
+      }
       else {
         generateDefaultBinOp(lExpr, rExpr, type);
       }
diff --git a/java/java-tests/testData/inspection/dataFlow/fixture/StringConcatAlwaysNotNull.java b/java/java-tests/testData/inspection/dataFlow/fixture/StringConcatAlwaysNotNull.java
new file mode 100644
index 000000000000..dd38e5a0fc9c
--- /dev/null
+++ b/java/java-tests/testData/inspection/dataFlow/fixture/StringConcatAlwaysNotNull.java
@@ -0,0 +1,15 @@
+import org.jetbrains.annotations.NotNull;
+
+class X {
+  @NotNull
+  String foo() {return "";}
+
+  void bar() {
+    String o = foo();
+    o += "";
+    if (<warning descr="Condition 'o != null' is always 'true'">o != null</warning>) {
+
+    }
+  }
+
+}
\ No newline at end of file
diff --git a/java/java-tests/testSrc/com/intellij/codeInspection/DataFlowInspectionTest.java b/java/java-tests/testSrc/com/intellij/codeInspection/DataFlowInspectionTest.java
index 36060cac29b6..fc5824cd047f 100644
--- a/java/java-tests/testSrc/com/intellij/codeInspection/DataFlowInspectionTest.java
+++ b/java/java-tests/testSrc/com/intellij/codeInspection/DataFlowInspectionTest.java
@@ -68,6 +68,7 @@ public class DataFlowInspectionTest extends LightCodeInsightFixtureTestCase {
   public void testIDEA84489() throws Throwable { doTest(); }
   public void testComparingToNotNullShouldNotAffectNullity() throws Throwable { doTest(); }
   public void testStringTernaryAlwaysTrue() throws Throwable { doTest(); }
+  public void testStringConcatAlwaysNotNull() throws Throwable { doTest(); }
 
   public void testNotNullPrimitive() throws Throwable { doTest(); }
   public void testBoxing128() throws Throwable { doTest(); }