target_sources: give a hint when a file named `FILE_SET` is not found

`FILE_SET` is only supported within `target_sources()` and only directly
after a visibility keyword or another `FILE_SET`. Give a hint as to what
might be wrong if a file named `FILE_SET` cannot be found for any
reason.

Fixes: #24539

8 files changed, 43 insertions, 0 deletions

diff --git a/Source/cmSourceFile.cxx b/Source/cmSourceFile.cxx
index 3fa0051..6224d0e 100644
--- a/Source/cmSourceFile.cxx
+++ b/Source/cmSourceFile.cxx
@@ -4,6 +4,9 @@
 
 #include <utility>
 
+#include <cm/string_view>
+#include <cmext/string_view>
+
 #include "cmGlobalGenerator.h"
 #include "cmListFileCache.h"
 #include "cmMakefile.h"
@@ -221,6 +224,11 @@ bool cmSourceFile::FindFullPath(std::string* error,
     case cmPolicies::NEW:
       break;
   }
+  if (lPath == "FILE_SET"_s) {
+    err += "\nHint: the FILE_SET keyword may only appear after a visibility "
+           "specifier or another FILE_SET within the target_sources() "
+           "command.";
+  }
   if (error != nullptr) {
     *error = std::move(err);
   } else {
diff --git a/Tests/RunCMake/target_sources/FileSetDirect-result.txt b/Tests/RunCMake/target_sources/FileSetDirect-result.txt
new file mode 100644
index 0000000..d00491f
--- /dev/null
+++ b/Tests/RunCMake/target_sources/FileSetDirect-result.txt
@@ -0,0 +1 @@
+1
diff --git a/Tests/RunCMake/target_sources/FileSetDirect-stderr.txt b/Tests/RunCMake/target_sources/FileSetDirect-stderr.txt
new file mode 100644
index 0000000..c1f7635
--- /dev/null
+++ b/Tests/RunCMake/target_sources/FileSetDirect-stderr.txt
@@ -0,0 +1,12 @@
+CMake Error at FileSetDirect.cmake:3 \(add_library\):
+  Cannot find source file:
+
+    FILE_SET
+
+  Tried extensions .c .C .c\+\+ .cc .cpp .cxx .cu .mpp .m .M .mm .ixx .cppm .h
+  .hh .h\+\+ .hm .hpp .hxx .in .txx .f .F .for .f77 .f90 .f95 .f03 .hip .ispc
+
+  Hint: the FILE_SET keyword may only appear after a visibility specifier or
+  another FILE_SET within the target_sources\(\) command.
+Call Stack \(most recent call first\):
+  CMakeLists.txt:3 \(include\)
diff --git a/Tests/RunCMake/target_sources/FileSetDirect.cmake b/Tests/RunCMake/target_sources/FileSetDirect.cmake
new file mode 100644
index 0000000..9f412c8
--- /dev/null
+++ b/Tests/RunCMake/target_sources/FileSetDirect.cmake
@@ -0,0 +1,3 @@
+enable_language(C)
+
+add_library(lib1 STATIC empty.c FILE_SET h1.h TYPE HEADERS)
diff --git a/Tests/RunCMake/target_sources/FileSetWrongSyntax-result.txt b/Tests/RunCMake/target_sources/FileSetWrongSyntax-result.txt
new file mode 100644
index 0000000..d00491f
--- /dev/null
+++ b/Tests/RunCMake/target_sources/FileSetWrongSyntax-result.txt
@@ -0,0 +1 @@
+1
diff --git a/Tests/RunCMake/target_sources/FileSetWrongSyntax-stderr.txt b/Tests/RunCMake/target_sources/FileSetWrongSyntax-stderr.txt
new file mode 100644
index 0000000..8722347
--- /dev/null
+++ b/Tests/RunCMake/target_sources/FileSetWrongSyntax-stderr.txt
@@ -0,0 +1,12 @@
+CMake Error at FileSetWrongSyntax.cmake:3 \(add_library\):
+  Cannot find source file:
+
+    FILE_SET
+
+  Tried extensions .c .C .c\+\+ .cc .cpp .cxx .cu .mpp .m .M .mm .ixx .cppm .h
+  .hh .h\+\+ .hm .hpp .hxx .in .txx .f .F .for .f77 .f90 .f95 .f03 .hip .ispc
+
+  Hint: the FILE_SET keyword may only appear after a visibility specifier or
+  another FILE_SET within the target_sources\(\) command.
+Call Stack \(most recent call first\):
+  CMakeLists.txt:3 \(include\)
diff --git a/Tests/RunCMake/target_sources/FileSetWrongSyntax.cmake b/Tests/RunCMake/target_sources/FileSetWrongSyntax.cmake
new file mode 100644
index 0000000..709fb23
--- /dev/null
+++ b/Tests/RunCMake/target_sources/FileSetWrongSyntax.cmake
@@ -0,0 +1,4 @@
+enable_language(C)
+
+add_library(lib1 STATIC)
+target_sources(lib1 PRIVATE empty.c FILE_SET h1.h TYPE HEADERS)
diff --git a/Tests/RunCMake/target_sources/RunCMakeTest.cmake b/Tests/RunCMake/target_sources/RunCMakeTest.cmake
index 7c67c3f..c1314f7 100644
--- a/Tests/RunCMake/target_sources/RunCMakeTest.cmake
+++ b/Tests/RunCMake/target_sources/RunCMakeTest.cmake
@@ -43,6 +43,8 @@ run_cmake(FileSetNoExistInstall)
 run_cmake(FileSetDirectories)
 run_cmake(FileSetCustomTarget)
 run_cmake(FileSetBadName)
+run_cmake(FileSetWrongSyntax)
+run_cmake(FileSetDirect)
 if(APPLE)
   run_cmake(FileSetFramework)
 endif()