Fix QShaderGenerator crashing when a node port name prefixed another one

QShaderGenerator didn't handle substitutions like
`vec4 $color = mix($color1, $color2, $fac);`

Note that `$color` is a prefix to `$color1` and `$color2`. For the
substitution `QByteArray::replace` was used so if `$color` was handled
first and replaced by `v1`, `$color1` and `$color2` were never correctly
replaced and instead became `v11` and `v12` which caused a crash later
on.

Change-Id: Idaf800fdac468f33c323eb722701da5f8eb918d6
Reviewed-by: Paul Lemire <paul.lemire@kdab.com>

src/gui/util/qshadergenerator.cpp

@@ -42,6 +42,8 @@
 #include "qshaderlanguage_p.h"
 #include <QRegularExpression>
 
+#include <cctype>
+
 QT_BEGIN_NAMESPACE
 
 Q_LOGGING_CATEGORY(ShaderGenerator, "ShaderGenerator", QtWarningMsg)
@@ -457,6 +459,13 @@ QByteArray QShaderGenerator::createShaderCode(const QStringList &enabledLayers)
         QByteArray line = node.rule(format).substitution;
         const QVector<QShaderNodePort> ports = node.ports();
 
+        struct VariableReplacement {
+            QByteArray placeholder;
+            QByteArray variable;
+        };
+
+        QVector<VariableReplacement> variableReplacements;
+
         // Generate temporary variable names vN
         for (const QShaderNodePort &port : ports) {
             const QString portName = port.name;
@@ -472,10 +481,37 @@ QByteArray QShaderGenerator::createShaderCode(const QStringList &enabledLayers)
             if (variableIndex < 0)
                 continue;
 
-            const auto placeholder = QByteArray(QByteArrayLiteral("$") + portName.toUtf8());
+            VariableReplacement replacement;
-            const auto variable = QByteArray(QByteArrayLiteral("v") + QByteArray::number(variableIndex));
+            replacement.placeholder = QByteArrayLiteral("$") + portName.toUtf8();
+            replacement.variable = QByteArrayLiteral("v") + QByteArray::number(variableIndex);
 
-            line.replace(placeholder, variable);
+            variableReplacements.append(std::move(replacement));
+        }
+
+        int begin = 0;
+        while ((begin = line.indexOf('$', begin)) != -1) {
+            int end = begin + 1;
+            char endChar = line.at(end);
+            const int size = line.size();
+            while (end < size && (std::isalnum(endChar) || endChar == '_')) {
+                ++end;
+                endChar = line.at(end);
+            }
+
+            const int placeholderLength = end - begin;
+
+            const QByteArray variableName = line.mid(begin, placeholderLength);
+            const auto replacementIt = std::find_if(variableReplacements.cbegin(), variableReplacements.cend(),
+                                              [&variableName](const VariableReplacement &replacement) {
+                return variableName == replacement.placeholder;
+            });
+
+            if (replacementIt != variableReplacements.cend()) {
+                line.replace(begin, placeholderLength, replacementIt->variable);
+                begin += replacementIt->variable.length();
+            } else {
+                begin = end;
+            }
         }
 
         // Substitute variable names by generated vN variable names

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

@@ -198,6 +198,7 @@ private slots:
     void shouldGenerateDifferentCodeDependingOnActiveLayers();
     void shouldUseGlobalVariableRatherThanTemporaries();
     void shouldGenerateTemporariesWisely();
+    void shouldHandlePortNamesPrefixingOneAnother();
 };
 
 void tst_QShaderGenerator::shouldHaveDefaultState()
@@ -1229,6 +1230,75 @@ void tst_QShaderGenerator::shouldGenerateTemporariesWisely()
     }
 }
 
+void tst_QShaderGenerator::shouldHandlePortNamesPrefixingOneAnother()
+{
+    // GIVEN
+    const auto gl4 = createFormat(QShaderFormat::OpenGLCoreProfile, 4, 0);
+
+    auto color1 = createNode({
+                                 createPort(QShaderNodePort::Output, "output")
+                             });
+    color1.addRule(gl4, QShaderNode::Rule("vec4 $output = color1;",
+                                          QByteArrayList() << "in vec4 color1;"));
+
+    auto color2 = createNode({
+                                 createPort(QShaderNodePort::Output, "output")
+                             });
+    color2.addRule(gl4, QShaderNode::Rule("vec4 $output = color2;",
+                                          QByteArrayList() << "in vec4 color2;"));
+
+    auto addColor = createNode({
+                                   createPort(QShaderNodePort::Output, "color"),
+                                   createPort(QShaderNodePort::Input, "color1"),
+                                   createPort(QShaderNodePort::Input, "color2"),
+                               });
+    addColor.addRule(gl4, QShaderNode::Rule("vec4 $color = $color1 + $color2;"));
+
+    auto shaderOutput = createNode({
+                                       createPort(QShaderNodePort::Input, "input")
+                                   });
+
+    shaderOutput.addRule(gl4, QShaderNode::Rule("shaderOutput = $input;",
+                                                QByteArrayList() << "out vec4 shaderOutput;"));
+
+    // WHEN
+    const auto graph = [=] {
+        auto res = QShaderGraph();
+
+        res.addNode(color1);
+        res.addNode(color2);
+        res.addNode(addColor);
+        res.addNode(shaderOutput);
+
+        res.addEdge(createEdge(color1.uuid(), "output", addColor.uuid(), "color1"));
+        res.addEdge(createEdge(color2.uuid(), "output", addColor.uuid(), "color2"));
+        res.addEdge(createEdge(addColor.uuid(), "color", shaderOutput.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"
+            << ""
+            << "in vec4 color1;"
+            << "in vec4 color2;"
+            << "out vec4 shaderOutput;"
+            << ""
+            << "void main()"
+            << "{"
+            << "    shaderOutput = ((color1 + color2));"
+            << "}"
+            << "";
+    QCOMPARE(code, expected.join("\n"));
+}
+
 QTEST_MAIN(tst_QShaderGenerator)
 
 #include "tst_qshadergenerator.moc"