QShaderGenerator: Allow more expressions in input nodes

Currently QShaderGenerator will crash when encountering some expressions
in input nodes.

For example, this node prototype would make it crash:
"VERTEX_COLOR": {
  "outputs": ["color", "alpha"],
  "rules": [
    "headerSnippets": ["in vec4 vertexColor;"],
    "substitution": "vec3 $color = vertexColor.rgb;
                     float $alpha = vertexColor.a;"
  ]
}

Change-Id: I37abb8099d376843a4cb13228140467dc1b8f60c
Reviewed-by: Paul Lemire <paul.lemire@kdab.com>
(cherry picked from commit f9086ebd0198c53e8a811af47e0ff0c84d78eb30)

src/gui/util/qshadergenerator.cpp

@@ -346,10 +346,9 @@ QByteArray QShaderGenerator::createShaderCode(const QStringList &enabledLayers)
     code << QByteArrayLiteral("void main()");
     code << QByteArrayLiteral("{");
 
-    const QRegularExpression localToGlobalRegExp(QStringLiteral("[^;]*\\s+(\\w+)\\s*=\\s*((?:\\w+\\(.*\\))|(?:\\w+))[^;]*;"));
     const QRegularExpression temporaryVariableToAssignmentRegExp(QStringLiteral("([^;]*\\s+(v\\d+))\\s*=\\s*([^;]*);"));
     const QRegularExpression temporaryVariableInAssignmentRegExp(QStringLiteral("\\W*(v\\d+)\\W*"));
-    const QRegularExpression outputToTemporaryAssignmentRegExp(QStringLiteral("\\s*(\\w+)\\s*=\\s*([^;]*);"));
+    const QRegularExpression statementRegExp(QStringLiteral("\\s*(\\w+)\\s*=\\s*([^;]*);"));
 
     struct Variable;
 
@@ -521,14 +520,12 @@ QByteArray QShaderGenerator::createShaderCode(const QStringList &enabledLayers)
 
         switch (node.type()) {
         case QShaderNode::Input:
-            matches = localToGlobalRegExp.globalMatch(QString::fromUtf8(substitutionedLine));
+        case QShaderNode::Output:
+            matches = statementRegExp.globalMatch(QString::fromUtf8(substitutionedLine));
             break;
         case QShaderNode::Function:
             matches = temporaryVariableToAssignmentRegExp.globalMatch(QString::fromUtf8(substitutionedLine));
             break;
-        case QShaderNode::Output:
-            matches = outputToTemporaryAssignmentRegExp.globalMatch(QString::fromUtf8(substitutionedLine));
-            break;
         case QShaderNode::Invalid:
             break;
         }

tests/auto/gui/util/qshadergenerator/tst_qshadergenerator.cpp

@@ -200,6 +200,7 @@ private slots:
     void shouldGenerateTemporariesWisely();
     void shouldHandlePortNamesPrefixingOneAnother();
     void shouldHandleNodesWithMultipleOutputPorts();
+    void shouldHandleExpressionsInInputNodes();
 };
 
 void tst_QShaderGenerator::shouldHaveDefaultState()
@@ -1372,6 +1373,55 @@ void tst_QShaderGenerator::shouldHandleNodesWithMultipleOutputPorts()
     QCOMPARE(code, expected.join("\n"));
 }
 
+void tst_QShaderGenerator::shouldHandleExpressionsInInputNodes()
+{
+    // GIVEN
+    const auto gl4 = createFormat(QShaderFormat::OpenGLCoreProfile, 4, 0);
+
+    auto input = createNode({
+                                createPort(QShaderNodePort::Output, "output")
+                            });
+    input.addRule(gl4, QShaderNode::Rule("float $output = 3 + 4;"));
+
+    auto output = createNode({
+                                 createPort(QShaderNodePort::Input, "input")
+                             });
+
+    output.addRule(gl4, QShaderNode::Rule("globalOut = $input;",
+                                          QByteArrayList() << "out float globalOut;"));
+
+    // WHEN
+    const auto graph = [=] {
+        auto res = QShaderGraph();
+
+        res.addNode(input);
+        res.addNode(output);
+
+        res.addEdge(createEdge(input.uuid(), "output", output.uuid(), "input"));
+
+        return res;
+    }();
+
+    auto generator = QShaderGenerator();
+    generator.graph = graph;
+    generator.format = gl4;
+
+    const auto code = generator.createShaderCode();
+
+    // THEN
+    const auto expected = QByteArrayList()
+            << "#version 400 core"
+            << ""
+            << "out float globalOut;"
+            << ""
+            << "void main()"
+            << "{"
+            << "    globalOut = 3 + 4;"
+            << "}"
+            << "";
+    QCOMPARE(code, expected.join("\n"));
+}
+
 QTEST_MAIN(tst_QShaderGenerator)
 
 #include "tst_qshadergenerator.moc"