VS: Fix GenerateDebugInformation values for v140 and v141 toolsets

When VS 2015 was first released, its new v140 toolset came with a
`link.xml` file that changed the `GenerateDebugInformation` boolean
(`false` and `true`) value from earlier toolsets to an enumeration
consisting of the possible values `No`, `Debug`, and `DebugFastLink`.

We first adapted to this in commit v3.4.2~2^2 (VS: Fix VS 2015 .vcxproj
file value for GenerateDebugInformation, 2016-01-08), but that broke
older toolsets that still expected the boolean.  Then commit
v3.6.0-rc1~295^2~1 (VS: Fix VS 2015 .vcxproj debug setting for older
toolsets, 2016-02-24) added a hack to fix up the value based on the
toolset in use.  Several follow-up commits fixed this for more older
toolsets because our flag table was at the time based on the generator
in use rather than the toolset in use.

Since commit v3.8.0-rc1~396^2 (VS: Choose flag map based on the toolset
name, 2016-10-17) we use a flag table based on the toolset, so the fixup
hack should not be needed.  We had to keep it around only due to our
default value for GenerateDebugInformation (`false` or `No`) still being
based on the generator instead of the toolset.

A VS 2015 update was released that changed the v140 toolset `link.xml`
file back to using `false` and `true` for the `GenerateDebugInformation`
enumeration variants previously known as `No` and `Debug`.  In order to
know which pair to use, we need to parse the `link.xml` file for the
current toolset.

Switch back to using `false` and `true` unconditionally in our
`GenerateDebugInformation` flag table entries and default value.  With
that plus the toolset-based flag table, we now get incorrect values for
`GenerateDebugInformation` only when using a v140 toolset from an older
VS 2015 installation.  Detect this case by parsing `link.xml` and add
special logic to convert `false` and `true` to `No` and `Debug` to
satisfy the older toolset specification.

Inspired-by: Ian Hojnicki <nullref@live.com>
Fixes: #17020

Source/cmGlobalVisualStudio10Generator.cxx

@@ -130,6 +130,7 @@ cmGlobalVisualStudio10Generator::cmGlobalVisualStudio10Generator(
   this->DefaultNasmFlagTable = cmVS10NASMFlagTable;
   this->DefaultRcFlagTable = cmVS10RCFlagTable;
   this->Version = VS10;
+  this->PlatformToolsetNeedsDebugEnum = false;
 }
 
 bool cmGlobalVisualStudio10Generator::MatchesGeneratorName(
@@ -195,6 +196,24 @@ bool cmGlobalVisualStudio10Generator::SetGeneratorToolset(
     return false;
   }
 
+  if (cmHasLiteralPrefix(this->GetPlatformToolsetString(), "v140")) {
+    // The GenerateDebugInformation link setting for the v140 toolset
+    // in VS 2015 was originally an enum with "No" and "Debug" values,
+    // differing from the "false" and "true" values used in older toolsets.
+    // A VS 2015 update changed it back.  Parse the "link.xml" file to
+    // discover which one we need.
+    std::string const link_xml = this->VCTargetsPath + "/1033/link.xml";
+    cmsys::ifstream fin(link_xml.c_str());
+    std::string line;
+    while (fin && cmSystemTools::GetLineFromStream(fin, line)) {
+      if (line.find(" Switch=\"DEBUG\" ") != std::string::npos) {
+        this->PlatformToolsetNeedsDebugEnum =
+          line.find(" Name=\"Debug\" ") != std::string::npos;
+        break;
+      }
+    }
+  }
+
   if (this->GeneratorToolsetCuda.empty()) {
     // Find the highest available version of the CUDA tools.
     std::vector<std::string> cudaTools;

Source/cmGlobalVisualStudio10Generator.h

@@ -59,6 +59,13 @@ public:
   const char* GetPlatformToolsetCuda() const;
   std::string const& GetPlatformToolsetCudaString() const;
 
+  /** Return whether we need to use No/Debug instead of false/true
+      for GenerateDebugInformation.  */
+  bool GetPlatformToolsetNeedsDebugEnum() const
+  {
+    return this->PlatformToolsetNeedsDebugEnum;
+  }
+
   /** Return the CMAKE_SYSTEM_NAME.  */
   std::string const& GetSystemName() const { return this->SystemName; }
 
@@ -169,6 +176,8 @@ private:
   virtual std::string FindDevEnvCommand();
   virtual std::string GetVSMakeProgram() { return this->GetMSBuildCommand(); }
 
+  bool PlatformToolsetNeedsDebugEnum;
+
   bool ParseGeneratorToolset(std::string const& ts, cmMakefile* mf);
 
   std::string VCTargetsPath;

Source/cmVS140LinkFlagTable.h

@@ -38,7 +38,7 @@ static cmVS7FlagTable cmVS140LinkFlagTable[] = {
   { "GenerateDebugInformation", "DEBUG:FASTLINK",
     "Optimize for faster linking", "DebugFastLink",
     cmVS7FlagTable::CaseInsensitive },
-  { "GenerateDebugInformation", "DEBUG", "Optimize for debugging", "Debug",
+  { "GenerateDebugInformation", "DEBUG", "Optimize for debugging", "true",
     cmVS7FlagTable::CaseInsensitive },
 
   { "SubSystem", "", "Not Set", "NotSet", 0 },

Source/cmVS141LinkFlagTable.h

@@ -38,7 +38,7 @@ static cmVS7FlagTable cmVS141LinkFlagTable[] = {
   { "GenerateDebugInformation", "DEBUG:FASTLINK",
     "Generate Debug Information optimized for faster links", "DebugFastLink",
     cmVS7FlagTable::CaseInsensitive },
-  { "GenerateDebugInformation", "DEBUG", "Generate Debug Information", "Debug",
+  { "GenerateDebugInformation", "DEBUG", "Generate Debug Information", "true",
     cmVS7FlagTable::CaseInsensitive },
 
   { "SubSystem", "", "Not Set", "NotSet", 0 },

Source/cmVisualStudio10TargetGenerator.cxx

@@ -17,8 +17,6 @@
 
 #include "cm_auto_ptr.hxx"
 
-static std::string const kWINDOWS_7_1_SDK = "Windows7.1SDK";
-
 static std::string cmVS10EscapeXML(std::string arg)
 {
   cmSystemTools::ReplaceString(arg, "&", "&");
@@ -3130,12 +3128,7 @@ bool cmVisualStudio10TargetGenerator::ComputeLinkOptions(
       linkOptions.AddFlag("StackReserveSize", stackVal);
     }
 
-    if (this->LocalGenerator->GetVersion() >=
-        cmGlobalVisualStudioGenerator::VS14) {
-      linkOptions.AddFlag("GenerateDebugInformation", "No");
-    } else {
-      linkOptions.AddFlag("GenerateDebugInformation", "false");
-    }
+    linkOptions.AddFlag("GenerateDebugInformation", "false");
 
     std::string pdb = this->GeneratorTarget->GetPDBDirectory(config.c_str());
     pdb += "/";
@@ -3182,26 +3175,14 @@ bool cmVisualStudio10TargetGenerator::ComputeLinkOptions(
                            "%(IgnoreSpecificDefaultLibraries)");
   }
 
-  // Hack to fix flag version selection in a common use case.
-  // FIXME: Select flag table based on toolset instead of VS version.
-  if (this->LocalGenerator->GetVersion() >=
-      cmGlobalVisualStudioGenerator::VS14) {
-    const char* toolset = gg->GetPlatformToolset();
-    if (toolset &&
-        (toolset == kWINDOWS_7_1_SDK || /* clang-format please break here */
-         cmHasLiteralPrefix(toolset, "v80") ||
-         cmHasLiteralPrefix(toolset, "v90") ||
-         cmHasLiteralPrefix(toolset, "v100") ||
-         cmHasLiteralPrefix(toolset, "v110") ||
-         cmHasLiteralPrefix(toolset, "v120"))) {
-      if (const char* debug =
-            linkOptions.GetFlag("GenerateDebugInformation")) {
-        // Convert value from enumeration back to boolean for older toolsets.
-        if (strcmp(debug, "No") == 0) {
-          linkOptions.AddFlag("GenerateDebugInformation", "false");
-        } else if (strcmp(debug, "Debug") == 0) {
-          linkOptions.AddFlag("GenerateDebugInformation", "true");
-        }
+  // VS 2015 without all updates has a v140 toolset whose
+  // GenerateDebugInformation expects No/Debug instead of false/true.
+  if (gg->GetPlatformToolsetNeedsDebugEnum()) {
+    if (const char* debug = linkOptions.GetFlag("GenerateDebugInformation")) {
+      if (strcmp(debug, "false") == 0) {
+        linkOptions.AddFlag("GenerateDebugInformation", "No");
+      } else if (strcmp(debug, "true") == 0) {
+        linkOptions.AddFlag("GenerateDebugInformation", "Debug");
       }
     }
   }