Merge pull request github#5824 from JLLeitschuh/feat/JLL/guava_first_non_null

[Java] Add support for com.google.common.base.MoreObjects#firstNonNull

Author: aschackmull

java/change-notes/2021-05-03-guava-first-non-null.md

@@ -0,0 +1,2 @@
+lgtm,codescanning
+* Increase coverage of the Guava framework by adding support for `com.google.common.base.MoreObjects#firstNonNull`.

java/ql/src/semmle/code/java/frameworks/guava/Base.qll

@@ -35,7 +35,8 @@ private class GuavaBaseCsv extends SummaryModelCsv {
         "com.google.common.base;Splitter;false;splitToList;(CharSequence);;Argument[0];ReturnValue;taint",
         "com.google.common.base;Splitter;false;splitToStream;(CharSequence);;Argument[0];ReturnValue;taint",
         "com.google.common.base;Splitter$MapSplitter;false;split;(CharSequence);;Argument[0];ReturnValue;taint",
-        "com.google.common.base;Preconditions;false;checkNotNull;;;Argument[0];ReturnValue;value"
+        "com.google.common.base;Preconditions;false;checkNotNull;;;Argument[0];ReturnValue;value",
+        "com.google.common.base;MoreObjects;false;firstNonNull;;;Argument[0..1];ReturnValue;value"
       ]
   }
 }

java/ql/test/library-tests/frameworks/guava/TestBase.java

@@ -60,4 +60,10 @@ void test3() {
     void test4() {
         sink(Preconditions.checkNotNull(taint())); // $numTaintFlow=1
     }
+
+    void test5() {
+        sink(MoreObjects.firstNonNull(taint(), taint())); // $numTaintFlow=2
+        sink(MoreObjects.firstNonNull(null, taint())); // $numTaintFlow=1
+        sink(MoreObjects.firstNonNull(taint(), null)); // $numTaintFlow=1
+    }
 }

java/ql/test/stubs/guava-30.0/com/google/common/base/MoreObjects.java

@@ -0,0 +1,9 @@
+package com.google.common.base;
+
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+public final class MoreObjects {
+    public static <T> T firstNonNull(@Nullable T first, @Nullable T second) {
+        return null;
+    }
+}