Introduce Rule.requiresInputs

This supports the use case of a rule that wants to create its output
even if no artifacts match the declared inputs. We have encountered it
several times in practice.

[ChangeLog] Introduced new property Rule.requiresInputs

Change-Id: If42ab347fb8e47b9117ac48fe3ce1b228566e0d8
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>

15 files changed, 111 insertions, 32 deletions

diff --git a/doc/reference/items/language/rule.qdoc b/doc/reference/items/language/rule.qdoc
index eff9a95ff..c089f19d3 100644
--- a/doc/reference/items/language/rule.qdoc
+++ b/doc/reference/items/language/rule.qdoc
@@ -282,6 +282,14 @@
             The argument \c{input} is \c{undefined} if there's more than one input artifact for this
             rule. Similarly, \c{output} is only defined if there's exactly one output artifact.
     \row
+        \li requiresInputs
+        \li bool
+        \li \c true if the rule declares any inputs, \c false otherwise
+        \li Specifies whether a rule's commands should be created even if no inputs are available.
+            Enabling this property can be useful in cases where you potentially have input files,
+            but it is possible that there are none and you want to create the output file in
+            any case.
+    \row
         \li alwaysRun
         \li bool
         \li false
diff --git a/src/lib/corelib/buildgraph/rulenode.cpp b/src/lib/corelib/buildgraph/rulenode.cpp
index 7b7ac7899..d4558787d 100644
--- a/src/lib/corelib/buildgraph/rulenode.cpp
+++ b/src/lib/corelib/buildgraph/rulenode.cpp
@@ -83,7 +83,7 @@ void RuleNode::apply(const Logger &logger, const ArtifactSet &changedInputs,
     const ArtifactSet addedInputs = allCompatibleInputs - m_oldInputArtifacts;
     const ArtifactSet removedInputs = m_oldInputArtifacts - allCompatibleInputs;
     result->upToDate = changedInputs.isEmpty() && addedInputs.isEmpty() && removedInputs.isEmpty()
-            && m_rule->requiresInputs();
+            && m_rule->declaresInputs() && m_rule->requiresInputs;
 
     if (logger.traceEnabled()) {
         logger.qbsTrace()
@@ -133,7 +133,7 @@ void RuleNode::apply(const Logger &logger, const ArtifactSet &changedInputs,
         }
         RulesApplicator::handleRemovedRuleOutputs(inputs, outputArtifactsToRemove, logger);
     }
-    if (!inputs.isEmpty() || !m_rule->requiresInputs()) {
+    if (!inputs.isEmpty() || !m_rule->declaresInputs() || !m_rule->requiresInputs) {
         RulesApplicator applicator(product.lock(), logger);
         applicator.applyRule(m_rule, inputs);
         result->createdNodes = applicator.createdArtifacts();
diff --git a/src/lib/corelib/buildgraph/rulesapplicator.cpp b/src/lib/corelib/buildgraph/rulesapplicator.cpp
index 08a778850..b10ae67b9 100644
--- a/src/lib/corelib/buildgraph/rulesapplicator.cpp
+++ b/src/lib/corelib/buildgraph/rulesapplicator.cpp
@@ -84,7 +84,7 @@ RulesApplicator::~RulesApplicator()
 
 void RulesApplicator::applyRule(const RuleConstPtr &rule, const ArtifactSet &inputArtifacts)
 {
-    if (inputArtifacts.isEmpty() && rule->requiresInputs())
+    if (inputArtifacts.isEmpty() && rule->declaresInputs() && rule->requiresInputs)
         return;
 
     m_createdArtifacts.clear();
@@ -339,7 +339,7 @@ Artifact *RulesApplicator::createOutputArtifact(const QString &filePath, const F
                               (*inputArtifacts.cbegin())->filePath()));
             throw error;
         }
-        if (m_rule->requiresInputs())
+        if (m_rule->declaresInputs())
             outputArtifact->clearTimestamp();
         m_invalidatedArtifacts += outputArtifact;
     } else {
diff --git a/src/lib/corelib/language/builtindeclarations.cpp b/src/lib/corelib/language/builtindeclarations.cpp
index 009e80ed1..bb9b79ada 100644
--- a/src/lib/corelib/language/builtindeclarations.cpp
+++ b/src/lib/corelib/language/builtindeclarations.cpp
@@ -421,6 +421,9 @@ void BuiltinDeclarations::addRuleItem()
     PropertyDeclaration decl(QLatin1String("multiplex"), PropertyDeclaration::Boolean);
     decl.setInitialValueSource(QLatin1String("false"));
     item << decl;
+    PropertyDeclaration requiresInputsDecl(QLatin1String("requiresInputs"),
+                                           PropertyDeclaration::Boolean);
+    item << requiresInputsDecl;
     item << PropertyDeclaration(QLatin1String("name"), PropertyDeclaration::String);
     item << PropertyDeclaration(QLatin1String("inputs"), PropertyDeclaration::StringList);
     item << PropertyDeclaration(QLatin1String("outputFileTags"), PropertyDeclaration::StringList);
diff --git a/src/lib/corelib/language/language.cpp b/src/lib/corelib/language/language.cpp
index f9c469032..c5aa34ae1 100644
--- a/src/lib/corelib/language/language.cpp
+++ b/src/lib/corelib/language/language.cpp
@@ -403,7 +403,7 @@ bool Rule::isDynamic() const
     return outputArtifactsScript->isValid();
 }
 
-bool Rule::requiresInputs() const
+bool Rule::declaresInputs() const
 {
     return !inputs.isEmpty() || !inputsFromDependencies.isEmpty();
 }
@@ -421,6 +421,7 @@ void Rule::load(PersistentPool &pool)
     pool.load(inputsFromDependencies);
     pool.load(explicitlyDependsOn);
     pool.load(multiplex);
+    pool.load(requiresInputs);
     pool.load(alwaysRun);
     pool.load(artifacts);
 }
@@ -438,6 +439,7 @@ void Rule::store(PersistentPool &pool) const
     pool.store(inputsFromDependencies);
     pool.store(explicitlyDependsOn);
     pool.store(multiplex);
+    pool.store(requiresInputs);
     pool.store(alwaysRun);
     pool.store(artifacts);
 }
@@ -1224,6 +1226,7 @@ bool operator==(const Rule &r1, const Rule &r2)
             && r1.inputsFromDependencies == r2.inputsFromDependencies
             && r1.explicitlyDependsOn == r2.explicitlyDependsOn
             && r1.multiplex == r2.multiplex
+            && r1.requiresInputs == r2.requiresInputs
             && r1.alwaysRun == r2.alwaysRun;
 }
 
diff --git a/src/lib/corelib/language/language.h b/src/lib/corelib/language/language.h
index 583b585e9..d65a12536 100644
--- a/src/lib/corelib/language/language.h
+++ b/src/lib/corelib/language/language.h
@@ -349,6 +349,7 @@ public:
     FileTags inputsFromDependencies;
     FileTags explicitlyDependsOn;
     bool multiplex;
+    bool requiresInputs;
     QList<RuleArtifactPtr> artifacts;           // unused, if outputFileTags/outputArtifactsScript is non-empty
     bool alwaysRun;
 
@@ -360,7 +361,7 @@ public:
     FileTags staticOutputFileTags() const;
     FileTags collectedOutputFileTags() const;
     bool isDynamic() const;
-    bool requiresInputs() const;
+    bool declaresInputs() const;
 private:
     Rule() : multiplex(false), alwaysRun(false), ruleGraphId(-1) {}
 
diff --git a/src/lib/corelib/language/projectresolver.cpp b/src/lib/corelib/language/projectresolver.cpp
index f4b20a412..0b81f6f4e 100644
--- a/src/lib/corelib/language/projectresolver.cpp
+++ b/src/lib/corelib/language/projectresolver.cpp
@@ -836,6 +836,11 @@ void ProjectResolver::resolveRule(Item *item, ProjectContext *projectContext)
     rule->inputs = m_evaluator->fileTagsValue(item, QLatin1String("inputs"));
     rule->inputsFromDependencies
             = m_evaluator->fileTagsValue(item, QLatin1String("inputsFromDependencies"));
+    bool requiresInputsSet = false;
+    rule->requiresInputs = m_evaluator->boolValue(item, QLatin1String("requiresInputs"), true,
+                                                  &requiresInputsSet);
+    if (!requiresInputsSet)
+        rule->requiresInputs = rule->declaresInputs();
     rule->auxiliaryInputs
             = m_evaluator->fileTagsValue(item, QLatin1String("auxiliaryInputs"));
     rule->excludedAuxiliaryInputs
@@ -843,12 +848,19 @@ void ProjectResolver::resolveRule(Item *item, ProjectContext *projectContext)
     rule->explicitlyDependsOn
             = m_evaluator->fileTagsValue(item, QLatin1String("explicitlyDependsOn"));
     rule->module = m_moduleContext ? m_moduleContext->module : projectContext->dummyModule;
-    if (!rule->multiplex && !rule->requiresInputs()) {
-        const QString message = Tr::tr("Rule has no inputs, but is not a multiplex rule.");
-        ErrorInfo error(message, item->location());
-        if (m_setupParams.productErrorMode() == ErrorHandlingMode::Strict)
-            throw error;
-        m_logger.printWarning(error);
+    if (!rule->multiplex && !rule->declaresInputs()) {
+        handleError(ErrorInfo(Tr::tr("Rule has no inputs, but is not a multiplex rule."),
+                              item->location()));
+        return;
+    }
+    if (!rule->multiplex && !rule->requiresInputs) {
+        handleError(ErrorInfo(Tr::tr("Rule.requiresInputs is false for non-multiplex rule.")
+                              , item->location()));
+        return;
+    }
+    if (!rule->declaresInputs() && rule->requiresInputs) {
+        handleError(ErrorInfo(Tr::tr("Rule.requiresInputs is true, but the rule "
+                                     "does not declare any input tags."), item->location()));
         return;
     }
     if (m_productContext)
@@ -1059,6 +1071,13 @@ void ProjectResolver::printProfilingInfo()
                                          .arg(elapsedTimeString(m_elapsedTimeGroups));
 }
 
+void ProjectResolver::handleError(const ErrorInfo &error)
+{
+    if (m_setupParams.productErrorMode() == ErrorHandlingMode::Strict)
+        throw error;
+    m_logger.printWarning(error);
+}
+
 static bool hasDependencyCycle(Set<ResolvedProduct *> *checked,
                                Set<ResolvedProduct *> *branch,
                                const ResolvedProductPtr &product,
diff --git a/src/lib/corelib/language/projectresolver.h b/src/lib/corelib/language/projectresolver.h
index 2b46c2093..f25db0651 100644
--- a/src/lib/corelib/language/projectresolver.h
+++ b/src/lib/corelib/language/projectresolver.h
@@ -146,6 +146,7 @@ private:
     static void matchArtifactProperties(const ResolvedProductPtr &product,
             const QList<SourceArtifactPtr> &artifacts);
     void printProfilingInfo();
+    void handleError(const ErrorInfo &error);
 
     Evaluator *m_evaluator;
     Logger &m_logger;
diff --git a/src/lib/qtprofilesetup/templates/qml.qbs b/src/lib/qtprofilesetup/templates/qml.qbs
index 8a5a1b9f8..0f3a9cb77 100644
--- a/src/lib/qtprofilesetup/templates/qml.qbs
+++ b/src/lib/qtprofilesetup/templates/qml.qbs
@@ -40,29 +40,11 @@ QtModule {
         fileTags: ["qt.qml.qml"]
     }
 
-    // This is needed for the case that there are no QML files in the project.
     Rule {
         condition: isStaticLibrary
         multiplex: true
-        Artifact {
-            filePath: "qml_plugin_import.dummy"
-            fileTags: ["qt.qml.import_dummy"]
-        }
-        prepare: {
-            var cmd = new JavaScriptCommand();
-            cmd.silent = true;
-            cmd.sourceCode = function() {
-                var f = new TextFile(output.filePath, TextFile.WriteOnly);
-                f.close();
-            }
-            return [cmd];
-        }
-    }
-
-    Rule {
-        condition: isStaticLibrary
-        multiplex: true
-        inputs: ["qt.qml.qml", "qt.qml.import_dummy"]
+        requiresInputs: false
+        inputs: ["qt.qml.qml"]
         outputFileTags: ["cpp", "qt.qml.pluginlist"]
         outputArtifacts: {
             var list = [];
diff --git a/tests/auto/blackbox/testdata/rule-with-non-required-inputs/a.inp b/tests/auto/blackbox/testdata/rule-with-non-required-inputs/a.inp
new file mode 100644
index 000000000..e69de29bb
--- /dev/null
+++ b/tests/auto/blackbox/testdata/rule-with-non-required-inputs/a.inp
diff --git a/tests/auto/blackbox/testdata/rule-with-non-required-inputs/b.inp b/tests/auto/blackbox/testdata/rule-with-non-required-inputs/b.inp
new file mode 100644
index 000000000..e69de29bb
--- /dev/null
+++ b/tests/auto/blackbox/testdata/rule-with-non-required-inputs/b.inp
diff --git a/tests/auto/blackbox/testdata/rule-with-non-required-inputs/c.inp b/tests/auto/blackbox/testdata/rule-with-non-required-inputs/c.inp
new file mode 100644
index 000000000..e69de29bb
--- /dev/null
+++ b/tests/auto/blackbox/testdata/rule-with-non-required-inputs/c.inp
diff --git a/tests/auto/blackbox/testdata/rule-with-non-required-inputs/rule-with-non-required-inputs.qbs b/tests/auto/blackbox/testdata/rule-with-non-required-inputs/rule-with-non-required-inputs.qbs
new file mode 100644
index 000000000..6719bc69d
--- /dev/null
+++ b/tests/auto/blackbox/testdata/rule-with-non-required-inputs/rule-with-non-required-inputs.qbs
@@ -0,0 +1,42 @@
+import qbs
+import qbs.TextFile
+
+Product {
+    name: "p"
+    type: ["p.out"]
+
+    property bool enableTagger
+
+    FileTagger {
+        condition: enableTagger
+        patterns: ["*.inp"]
+        fileTags: ["p.in"]
+    }
+
+    Rule {
+        multiplex: true
+        requiresInputs: false
+        inputs: ["p.in"]
+        Artifact {
+            filePath: "output.txt"
+            fileTags: ["p.out"]
+        }
+        prepare: {
+            var cmd = new JavaScriptCommand();
+            cmd.description = "Generating " + output.fileName;
+            cmd.sourceCode = function() {
+                var f = new TextFile(output.filePath, TextFile.WriteOnly);
+                f.write('(');
+                var inputsList = inputs["p.in"];
+                if (inputsList) {
+                    for (var i = 0; i < inputsList.length; ++i)
+                        f.write(inputsList[i].fileName + ',');
+                }
+                f.write(')');
+            };
+            return [cmd];
+        }
+    }
+
+    files: ["a.inp", "b.inp", "c.inp"]
+}
diff --git a/tests/auto/blackbox/tst_blackbox.cpp b/tests/auto/blackbox/tst_blackbox.cpp
index 0bdb9c81f..a7371c8a6 100644
--- a/tests/auto/blackbox/tst_blackbox.cpp
+++ b/tests/auto/blackbox/tst_blackbox.cpp
@@ -1598,6 +1598,25 @@ void TestBlackbox::ruleWithNoInputs()
     QVERIFY2(m_qbsStdout.contains("creating output"), m_qbsStdout.constData());
 }
 
+void TestBlackbox::ruleWithNonRequiredInputs()
+{
+    QDir::setCurrent(testDataDir + "/rule-with-non-required-inputs");
+    QbsRunParameters params("build", {"products.p.enableTagger:false"});
+    QCOMPARE(runQbs(params), 0);
+    QFile outFile(relativeProductBuildDir("p") + "/output.txt");
+    QVERIFY2(outFile.open(QIODevice::ReadOnly), qPrintable(outFile.errorString()));
+    QByteArray output = outFile.readAll();
+    QCOMPARE(output, QByteArray("()"));
+    outFile.close();
+    params.command = "resolve";
+    params.arguments = QStringList({"products.p.enableTagger:true"});
+    QCOMPARE(runQbs(params), 0);
+    QCOMPARE(runQbs(), 0);
+    QVERIFY2(outFile.open(QIODevice::ReadOnly), qPrintable(outFile.errorString()));
+    output = outFile.readAll();
+    QCOMPARE(output, QByteArray("(a.inp,b.inp,c.inp,)"));
+}
+
 void TestBlackbox::smartRelinking()
 {
     QDir::setCurrent(testDataDir + "/smart-relinking");
diff --git a/tests/auto/blackbox/tst_blackbox.h b/tests/auto/blackbox/tst_blackbox.h
index 83d8420e4..77f5762fb 100644
--- a/tests/auto/blackbox/tst_blackbox.h
+++ b/tests/auto/blackbox/tst_blackbox.h
@@ -156,6 +156,7 @@ private slots:
     void ruleConditions();
     void ruleCycle();
     void ruleWithNoInputs();
+    void ruleWithNonRequiredInputs();
     void smartRelinking();
     void smartRelinking_data();
     void soVersion();