ctest: add option for output truncation

Add `--test-output-truncation` to `ctest`. This option can be used to
customize which part of the test output is being truncated. Currently
supported values are `tail`, `middle` and `head`.

Also add equivalent `CTEST_CUSTOM_TEST_OUTPUT_TRUNCATION` variable.

Fixes: #23206

5 files changed, 73 insertions, 17 deletions

diff --git a/Source/CTest/cmCTestMemCheckHandler.cxx b/Source/CTest/cmCTestMemCheckHandler.cxx
index 6bb8e79..2d8276a 100644
--- a/Source/CTest/cmCTestMemCheckHandler.cxx
+++ b/Source/CTest/cmCTestMemCheckHandler.cxx
@@ -371,7 +371,8 @@ void cmCTestMemCheckHandler::GenerateCTestXML(cmXMLWriter& xml)
     }
     this->CleanTestOutput(
       memcheckstr,
-      static_cast<size_t>(this->CustomMaximumFailedTestOutputSize));
+      static_cast<size_t>(this->CustomMaximumFailedTestOutputSize),
+      this->TestOutputTruncation);
     this->WriteTestResultHeader(xml, result);
     xml.StartElement("Results");
     int memoryErrors = 0;
diff --git a/Source/CTest/cmCTestRunTest.cxx b/Source/CTest/cmCTestRunTest.cxx
index 6cd3b09..f594300 100644
--- a/Source/CTest/cmCTestRunTest.cxx
+++ b/Source/CTest/cmCTestRunTest.cxx
@@ -277,7 +277,8 @@ bool cmCTestRunTest::EndTest(size_t completed, size_t total, bool started)
       static_cast<size_t>(
         this->TestResult.Status == cmCTestTestHandler::COMPLETED
           ? this->TestHandler->CustomMaximumPassedTestOutputSize
-          : this->TestHandler->CustomMaximumFailedTestOutputSize));
+          : this->TestHandler->CustomMaximumFailedTestOutputSize),
+      this->TestHandler->TestOutputTruncation);
   }
   this->TestResult.Reason = reason;
   if (this->TestHandler->LogFile) {
diff --git a/Source/CTest/cmCTestTestHandler.cxx b/Source/CTest/cmCTestTestHandler.cxx
index 958c51c..a794e3d 100644
--- a/Source/CTest/cmCTestTestHandler.cxx
+++ b/Source/CTest/cmCTestTestHandler.cxx
@@ -281,6 +281,7 @@ cmCTestTestHandler::cmCTestTestHandler()
 
   this->CustomMaximumPassedTestOutputSize = 1 * 1024;
   this->CustomMaximumFailedTestOutputSize = 300 * 1024;
+  this->TestOutputTruncation = cmCTestTypes::TruncationMode::Tail;
 
   this->MemCheck = false;
 
@@ -325,6 +326,7 @@ void cmCTestTestHandler::Initialize()
   this->CustomPostTest.clear();
   this->CustomMaximumPassedTestOutputSize = 1 * 1024;
   this->CustomMaximumFailedTestOutputSize = 300 * 1024;
+  this->TestOutputTruncation = cmCTestTypes::TruncationMode::Tail;
 
   this->TestsToRun.clear();
 
@@ -358,6 +360,11 @@ void cmCTestTestHandler::PopulateCustomVectors(cmMakefile* mf)
   this->CTest->PopulateCustomInteger(
     mf, "CTEST_CUSTOM_MAXIMUM_FAILED_TEST_OUTPUT_SIZE",
     this->CustomMaximumFailedTestOutputSize);
+
+  cmValue dval = mf->GetDefinition("CTEST_CUSTOM_TEST_OUTPUT_TRUNCATION");
+  if (dval) {
+    this->SetTestOutputTruncation(dval);
+  }
 }
 
 int cmCTestTestHandler::PreProcessHandler()
@@ -2076,6 +2083,20 @@ void cmCTestTestHandler::SetExcludeRegExp(const std::string& arg)
   this->ExcludeRegExp = arg;
 }
 
+bool cmCTestTestHandler::SetTestOutputTruncation(const std::string& mode)
+{
+  if (mode == "tail") {
+    this->TestOutputTruncation = cmCTestTypes::TruncationMode::Tail;
+  } else if (mode == "middle") {
+    this->TestOutputTruncation = cmCTestTypes::TruncationMode::Middle;
+  } else if (mode == "head") {
+    this->TestOutputTruncation = cmCTestTypes::TruncationMode::Head;
+  } else {
+    return false;
+  }
+  return true;
+}
+
 void cmCTestTestHandler::SetTestsToRunInformation(cmValue in)
 {
   if (!in) {
@@ -2094,7 +2115,8 @@ void cmCTestTestHandler::SetTestsToRunInformation(cmValue in)
   }
 }
 
-void cmCTestTestHandler::CleanTestOutput(std::string& output, size_t length)
+void cmCTestTestHandler::CleanTestOutput(std::string& output, size_t length,
+                                         cmCTestTypes::TruncationMode truncate)
 {
   if (!length || length >= output.size() ||
       output.find("CTEST_FULL_OUTPUT") != std::string::npos) {
@@ -2122,20 +2144,29 @@ void cmCTestTestHandler::CleanTestOutput(std::string& output, size_t length)
     return current;
   };
 
-  // Truncate at given length respecting UTF-8 words
+  // Truncation message.
+  const std::string msg =
+    "\n[This part of the test output was removed since it "
+    "exceeds the threshold of " +
+    std::to_string(length) + " bytes.]\n";
+
   char const* const begin = output.c_str();
   char const* const end = begin + output.size();
-  char const* current = utf8_advance(begin, end, length);
-  output.erase(current - begin);
-
-  // Append truncation message.
-  std::ostringstream msg;
-  msg << "...\n"
-         "The rest of the test output was removed since it exceeds the "
-         "threshold "
-         "of "
-      << length << " bytes.\n";
-  output += msg.str();
+
+  // Erase head, middle or tail of output.
+  if (truncate == cmCTestTypes::TruncationMode::Head) {
+    char const* current = utf8_advance(begin, end, output.size() - length);
+    output.erase(0, current - begin);
+    output.insert(0, msg + "...");
+  } else if (truncate == cmCTestTypes::TruncationMode::Middle) {
+    char const* current = utf8_advance(begin, end, length / 2);
+    output.erase(current - begin, output.size() - length);
+    output.insert(current - begin, "..." + msg + "...");
+  } else { // default or "tail"
+    char const* current = utf8_advance(begin, end, length);
+    output.erase(current - begin);
+    output += ("..." + msg);
+  }
 }
 
 bool cmCTestTestHandler::SetTestsProperties(
diff --git a/Source/CTest/cmCTestTestHandler.h b/Source/CTest/cmCTestTestHandler.h
index 135e764..d0049da 100644
--- a/Source/CTest/cmCTestTestHandler.h
+++ b/Source/CTest/cmCTestTestHandler.h
@@ -19,6 +19,7 @@
 #include "cmCTest.h"
 #include "cmCTestGenericHandler.h"
 #include "cmCTestResourceSpec.h"
+#include "cmCTestTypes.h"
 #include "cmDuration.h"
 #include "cmListFileCache.h"
 #include "cmValue.h"
@@ -32,6 +33,7 @@ class cmXMLWriter;
  */
 class cmCTestTestHandler : public cmCTestGenericHandler
 {
+  friend class cmCTest;
   friend class cmCTestRunTest;
   friend class cmCTestMultiProcessHandler;
 
@@ -80,6 +82,9 @@ public:
     this->CustomMaximumFailedTestOutputSize = n;
   }
 
+  //! Set test output truncation mode. Return false if unknown mode.
+  bool SetTestOutputTruncation(const std::string& mode);
+
   //! pass the -I argument down
   void SetTestsToRunInformation(cmValue);
 
@@ -242,8 +247,9 @@ protected:
   void AttachFile(cmXMLWriter& xml, std::string const& file,
                   std::string const& name);
 
-  //! Clean test output to specified length
-  void CleanTestOutput(std::string& output, size_t length);
+  //! Clean test output to specified length and truncation mode
+  void CleanTestOutput(std::string& output, size_t length,
+                       cmCTestTypes::TruncationMode truncate);
 
   cmDuration ElapsedTestingTime;
 
@@ -258,6 +264,7 @@ protected:
   bool MemCheck;
   int CustomMaximumPassedTestOutputSize;
   int CustomMaximumFailedTestOutputSize;
+  cmCTestTypes::TruncationMode TestOutputTruncation;
   int MaxIndex;
 
 public:
diff --git a/Source/CTest/cmCTestTypes.h b/Source/CTest/cmCTestTypes.h
new file mode 100644
index 0000000..843d27a
--- /dev/null
+++ b/Source/CTest/cmCTestTypes.h
@@ -0,0 +1,16 @@
+/* Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
+   file Copyright.txt or https://cmake.org/licensing for details.  */
+
+#pragma once
+
+#include "cmConfigure.h" // IWYU pragma: keep
+
+namespace cmCTestTypes {
+
+enum class TruncationMode
+{ // Test output truncation mode
+  Tail,
+  Middle,
+  Head
+};
+}