[P4Testgen] Fix behavior of coverage on edge cases with no nodes to cover

backends/p4tools/common/options.cpp

@@ -78,6 +78,10 @@ std::optional<ICompileContext *> AbstractP4cToolOptions::process(
     }
     P4CContext::get().options().file = remainingArgs->at(0);
 
+    if (!validateOptions()) {
+        return std::nullopt;
+    }
+
     return compilerContext;
 }
 

backends/p4tools/common/options.h

@@ -33,6 +33,10 @@ class AbstractP4cToolOptions : protected Util::Options {
     /// Hook for customizing options processing.
     std::vector<const char *> *process(int argc, char *const argv[]) override;
 
+    /// Checks if parsed options make sense with respect to each-other.
+    /// @returns true if the validation was successfull and false otherwise.
+    virtual bool validateOptions() const { return true; }
+
     /// Converts a vector of command-line arguments into the traditional (argc, argv) format.
     static std::tuple<int, char **> convertArgs(const std::vector<const char *> &args);
 

backends/p4tools/modules/testgen/lib/test_backend.cpp

@@ -122,8 +122,13 @@ bool TestBackEnd::run(const FinalState &state) {
         }
 
         const P4::Coverage::CoverageSet &visitedNodes = symbex.getVisitedNodes();
-        if (coverableNodes.empty()) {
+        if (!testgenOptions.hasCoverageTracking) {
             printFeature("test_info", 4, "============ Test %1% ============", testCount);
+        } else if (coverableNodes.empty()) {
+            printFeature("test_info", 4,
+                         "============ Test %1%: No coverable nodes ============", testCount);
+            // All 0 nodes covered.
+            coverage = 1.0;
         } else {
             coverage =
                 static_cast<float>(visitedNodes.size()) / static_cast<float>(coverableNodes.size());

backends/p4tools/modules/testgen/options.cpp

@@ -259,6 +259,7 @@ TestgenOptions::TestgenOptions()
                 "STATEMENTS",
                 "TABLE_ENTRIES",
             };
+            hasCoverageTracking = true;
             auto selectionString = cstring(arg).toUpper();
             auto it = COVERAGE_OPTIONS.find(selectionString);
             if (it != COVERAGE_OPTIONS.end()) {
@@ -382,4 +383,16 @@ TestgenOptions::TestgenOptions()
         "produce no tests or only tests that contain counter examples.");
 }
 
+bool TestgenOptions::validateOptions() const {
+    if (minCoverage > 0 && !hasCoverageTracking) {
+        ::error(
+            ErrorType::ERR_INVALID,
+            "It is not allowed to have --assert-min-coverage set to non-zero without a coverage "
+            "tracking enabled with --track-coverage option. Without coverage tracking, the "
+            "--assert-min-coverage is meaningless.");
+        return false;
+    }
+    return true;
+}
+
 }  // namespace P4Tools::P4Testgen

backends/p4tools/modules/testgen/options.h

@@ -83,11 +83,18 @@ class TestgenOptions : public AbstractP4cToolOptions {
     /// Multiple options are possible. Currently supported: STATEMENTS, TABLE_ENTRIES.
     P4::Coverage::CoverageOptions coverageOptions;
 
+    /// Indicates that coverage tracking is enabled for some coverage criteria. This is used for
+    /// sanity checking and it also affects information printed to output.
+    bool hasCoverageTracking = false;
+
     /// Specifies minimum coverage that needs to be achieved for P4Testgen to exit successfully.
     float minCoverage = 0;
 
     const char *getIncludePath() override;
 
+ protected:
+    bool validateOptions() const override;
+
  private:
     TestgenOptions();
 };