qmake: Fix overlong command lines for static Qt builds on Windows

Linker response files for the MinGW and Unix makefile generators are
controlled by the variable QMAKE_LINK_OBJECT_MAX.  This variable holds a
number.  If the number of object files passed to the linker exceeds this
number, a linker response file containing object file paths is created.

This heuristic is extremely imprecise.  It doesn't take into account the
length of object file names nor the length of $$OBJECTS_DIR.

Also, when using a static Qt, a big part of the linker command line are
libraries.  A relatively small example can fail to link with "The
command line is too long" on Windows, even with the object files being
in a response file.

The MinGW makefile generator already reads the variable
QMAKE_RESPONSEFILE_THRESHOLD for compiler response files.  Re-use this
variable for the linker response file of the Unix and MinGW makefile
generators.

If QMAKE_RESPONSEFILE_THRESHOLD is set, use it to determine whether to
create a response file.  QMAKE_LINK_OBJECT_MAX is then ignored.  The
response file contains objects and libraries.

If QMAKE_RESPONSEFILE_THRESHOLD is not set, use QMAKE_LINK_OBJECT_MAX to
determine whether to create a response file.  The response file contains
only object files.

QMAKE_LINK_OBJECT_SCRIPT is used in both cases to specify a common base
name of all linker response files.

Pick-to: 6.2 6.3
Task-number: QTBUG-100559
Change-Id: I3c78354fa5ebb1a86438ec804679e0ee776c3f49
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Kai Koehne <kai.koehne@qt.io>

2 files changed, 10 insertions, 9 deletions

diff --git a/qmake/generators/win32/mingw_make.cpp b/qmake/generators/win32/mingw_make.cpp
index 823b799eb2..59fcb34ad8 100644
--- a/qmake/generators/win32/mingw_make.cpp
+++ b/qmake/generators/win32/mingw_make.cpp
@@ -242,21 +242,18 @@ void MingwMakefileGenerator::writeLibsPart(QTextStream &t)
 
 void MingwMakefileGenerator::writeObjectsPart(QTextStream &t)
 {
-    const ProString &objmax = project->first("QMAKE_LINK_OBJECT_MAX");
-    if (objmax.isEmpty() || project->values("OBJECTS").count() < objmax.toInt()) {
+    linkerResponseFile = maybeCreateLinkerResponseFile();
+    if (!linkerResponseFile.isValid()) {
         objectsLinkLine = "$(OBJECTS)";
     } else if (project->isActiveConfig("staticlib") && project->first("TEMPLATE") == "lib") {
         // QMAKE_LIB is used for win32, including mingw, whereas QMAKE_AR is used on Unix.
         QString ar_cmd = var("QMAKE_LIB");
         if (ar_cmd.isEmpty())
             ar_cmd = "ar -rc";
-        const QString ar_response_file =
-                createResponseFile(var("QMAKE_LINK_OBJECT_SCRIPT"), project->values("OBJECTS"));
-        objectsLinkLine = ar_cmd + ' ' + var("DEST_TARGET") + " @" + escapeFilePath(ar_response_file);
+        objectsLinkLine = ar_cmd + ' ' + var("DEST_TARGET") + " @"
+            + escapeFilePath(linkerResponseFile.filePath);
     } else {
-        const QString ld_response_file =
-                createResponseFile(var("QMAKE_LINK_OBJECT_SCRIPT"), project->values("OBJECTS"));
-        objectsLinkLine = "@" + escapeFilePath(ld_response_file);
+        objectsLinkLine = "@" + escapeFilePath(linkerResponseFile.filePath);
     }
     Win32MakefileGenerator::writeObjectsPart(t);
 }
@@ -284,7 +281,10 @@ void MingwMakefileGenerator::writeBuildRulesPart(QTextStream &t)
             t << "\n\t" << objectsLinkLine << " " ;
         }
     } else {
-        t << "\n\t$(LINKER) $(LFLAGS) " << var("QMAKE_LINK_O_FLAG") << "$(DESTDIR_TARGET) " << objectsLinkLine << "  $(LIBS)";
+        t << "\n\t$(LINKER) $(LFLAGS) " << var("QMAKE_LINK_O_FLAG") << "$(DESTDIR_TARGET) "
+          << objectsLinkLine;
+        if (!linkerResponseFile.isValid() || linkerResponseFile.onlyObjects)
+            t << " $(LIBS)";
     }
     if(!project->isEmpty("QMAKE_POST_LINK"))
         t << "\n\t" <<var("QMAKE_POST_LINK");
diff --git a/qmake/generators/win32/mingw_make.h b/qmake/generators/win32/mingw_make.h
index 6c1f0086cc..645a73c374 100644
--- a/qmake/generators/win32/mingw_make.h
+++ b/qmake/generators/win32/mingw_make.h
@@ -59,6 +59,7 @@ private:
     LibFlagType parseLibFlag(const ProString &flag, ProString *arg) override;
 
     QString objectsLinkLine;
+    LinkerResponseFileInfo linkerResponseFile;
 };
 
 QT_END_NAMESPACE