cxxmodules: Add more suggestions to no-modules-support diagnostics

Tell users what generators *do* support C++ modules.  Report the current
generator to make clear it is not one of those supporting modules.
Also clarify the purpose of the existing documentation references.

5 files changed, 49 insertions, 14 deletions

diff --git a/Tests/RunCMake/CXXModules/NoCXX-stderr.txt b/Tests/RunCMake/CXXModules/NoCXX-stderr.txt
index ba2715b..2ca67d6 100644
--- a/Tests/RunCMake/CXXModules/NoCXX-stderr.txt
+++ b/Tests/RunCMake/CXXModules/NoCXX-stderr.txt
@@ -3,8 +3,15 @@
   language has not been enabled\.
 |CMake Error in CMakeLists.txt:
   The target named "nocxx" has C\+\+ sources that may use modules, but modules
-  are not supported by this generator\.  See the cmake-cxxmodules\(7\) manual
-  and the CMAKE_CXX_SCAN_FOR_MODULES variable\.
+  are not supported by this generator:
+
+    [^
+]+
+
+  Modules are supported only by Ninja, Ninja Multi-Config, and Visual Studio
+  generators for VS 17\.4 and newer\.  See the cmake-cxxmodules\(7\) manual for
+  details\.  Use the CMAKE_CXX_SCAN_FOR_MODULES variable to enable or disable
+  scanning\.
 |CMake Error in CMakeLists.txt:
   Target "nocxx" has source file
 
diff --git a/Tests/RunCMake/CXXModules/NoCXX20-stderr.txt b/Tests/RunCMake/CXXModules/NoCXX20-stderr.txt
index 3f3a547..16adba5 100644
--- a/Tests/RunCMake/CXXModules/NoCXX20-stderr.txt
+++ b/Tests/RunCMake/CXXModules/NoCXX20-stderr.txt
@@ -4,6 +4,13 @@
   "cxx_std_17"\.
 |CMake Error in CMakeLists.txt:
   The target named "nocxx20" has C\+\+ sources that may use modules, but
-  modules are not supported by this generator\.  See the cmake-cxxmodules\(7\)
-  manual and the CMAKE_CXX_SCAN_FOR_MODULES variable\.
+  modules are not supported by this generator:
+
+    [^
+]+
+
+  Modules are supported only by Ninja, Ninja Multi-Config, and Visual Studio
+  generators for VS 17\.4 and newer\.  See the cmake-cxxmodules\(7\) manual for
+  details\.  Use the CMAKE_CXX_SCAN_FOR_MODULES variable to enable or disable
+  scanning\.
 )
diff --git a/Tests/RunCMake/CXXModules/NoDyndepSupport-stderr.txt b/Tests/RunCMake/CXXModules/NoDyndepSupport-stderr.txt
index c7e2979..5452ddb 100644
--- a/Tests/RunCMake/CXXModules/NoDyndepSupport-stderr.txt
+++ b/Tests/RunCMake/CXXModules/NoDyndepSupport-stderr.txt
@@ -7,6 +7,13 @@
   due to lack of required features\.  Ninja 1\.11 or higher is required\.
 |CMake Error in CMakeLists.txt:
   The target named "nodyndep" has C\+\+ sources that may use modules, but
-  modules are not supported by this generator\.  See the cmake-cxxmodules\(7\)
-  manual and the CMAKE_CXX_SCAN_FOR_MODULES variable\.
+  modules are not supported by this generator:
+
+    [^
+]+
+
+  Modules are supported only by Ninja, Ninja Multi-Config, and Visual Studio
+  generators for VS 17\.4 and newer\.  See the cmake-cxxmodules\(7\) manual for
+  details\.  Use the CMAKE_CXX_SCAN_FOR_MODULES variable to enable or disable
+  scanning\.
 )
diff --git a/Tests/RunCMake/CXXModules/NoScanningSourceFileProperty-stderr.txt b/Tests/RunCMake/CXXModules/NoScanningSourceFileProperty-stderr.txt
index ed78672..ce548b9 100644
--- a/Tests/RunCMake/CXXModules/NoScanningSourceFileProperty-stderr.txt
+++ b/Tests/RunCMake/CXXModules/NoScanningSourceFileProperty-stderr.txt
@@ -1,10 +1,17 @@
 (CMake Error in CMakeLists.txt:
   The target named "noscanning-sf-property" has C\+\+ sources that may use
   modules, but the compiler does not provide a way to discover the import
-  graph dependencies\.  See the cmake-cxxmodules\(7\) manual and the
-  CMAKE_CXX_SCAN_FOR_MODULES variable\.
+  graph dependencies\.  See the cmake-cxxmodules\(7\) manual for details\.  Use
+  the CMAKE_CXX_SCAN_FOR_MODULES variable to enable or disable scanning\.
 |CMake Error in CMakeLists.txt:
   The target named "noscanning-sf-property" has C\+\+ sources that may use
-  modules, but modules are not supported by this generator\.  See the
-  cmake-cxxmodules\(7\) manual and the CMAKE_CXX_SCAN_FOR_MODULES variable\.
+  modules, but modules are not supported by this generator:
+
+    [^
+]+
+
+  Modules are supported only by Ninja, Ninja Multi-Config, and Visual Studio
+  generators for VS 17\.4 and newer\.  See the cmake-cxxmodules\(7\) manual for
+  details\.  Use the CMAKE_CXX_SCAN_FOR_MODULES variable to enable or disable
+  scanning\.
 )
diff --git a/Tests/RunCMake/CXXModules/NoScanningTargetProperty-stderr.txt b/Tests/RunCMake/CXXModules/NoScanningTargetProperty-stderr.txt
index 9dfb3e9..a72fd16 100644
--- a/Tests/RunCMake/CXXModules/NoScanningTargetProperty-stderr.txt
+++ b/Tests/RunCMake/CXXModules/NoScanningTargetProperty-stderr.txt
@@ -1,10 +1,17 @@
 (CMake Error in CMakeLists.txt:
   The target named "noscanning-target-property" has C\+\+ sources that may use
   modules, but the compiler does not provide a way to discover the import
-  graph dependencies\.  See the cmake-cxxmodules\(7\) manual and the
-  CMAKE_CXX_SCAN_FOR_MODULES variable\.
+  graph dependencies\.  See the cmake-cxxmodules\(7\) manual for details\.  Use
+  the CMAKE_CXX_SCAN_FOR_MODULES variable to enable or disable scanning\.
 |CMake Error in CMakeLists.txt:
   The target named "noscanning-target-property" has C\+\+ sources that may use
-  modules, but modules are not supported by this generator\.  See the
-  cmake-cxxmodules\(7\) manual and the CMAKE_CXX_SCAN_FOR_MODULES variable\.
+  modules, but modules are not supported by this generator:
+
+    [^
+]+
+
+  Modules are supported only by Ninja, Ninja Multi-Config, and Visual Studio
+  generators for VS 17\.4 and newer\.  See the cmake-cxxmodules\(7\) manual for
+  details\.  Use the CMAKE_CXX_SCAN_FOR_MODULES variable to enable or disable
+  scanning\.
 )