Fix highlighting of escaped $< in CMake regex strings (#5028)

CHANGELOG.md

@@ -27,6 +27,7 @@ Improvements:
 - Embed the source commit SHA as a `commitId` field in the packaged extension's `package.json` so the exact commit a (pre-)release was built from can be identified, since the marketplace version number alone cannot be traced back to a commit. [#4801](https://github.com/microsoft/vscode-cmake-tools/issues/4801)
 
 Bug Fixes:
+- Fix CMake syntax highlighting treating escaped `$<` sequences in quoted regex strings as generator expressions. [#5028](https://github.com/microsoft/vscode-cmake-tools/issues/5028)
 - Fix a test run that matched no tests being reported as success. When specific tests are requested (e.g. programmatically via the API/Copilot) but none match a discovered test — for example an agent passing a partial or non-existent test name — CTest exits 0 ("No tests were found!!!"), which callers could misread as "all tests passed". Such runs now return a failure with a clear message when tests exist but the requested ones weren't found. [#4915](https://github.com/microsoft/vscode-cmake-tools/issues/4915)
 - Stop showing "Adding a file without a valid code model" / "Deleting a file without a valid code model" warning notifications when a source file is automatically added or deleted and there is no valid CMake code model (for example when using clangd with the C/C++ IntelliSense engine disabled, or before the project has been configured). The automatic list-file update now stays silent in this case; the warning is only shown when the update is explicitly invoked via the "CMake: Add new source file" / "CMake: Remove deleted source file" commands. [#5009](https://github.com/microsoft/vscode-cmake-tools/issues/5009)
 - Fix running a single test from the inline Test CodeLens or the project outline building the default (or all) target instead of the test's own executable; single-test runs now build only that test's target.

syntaxes/CMake.tmLanguage.json

@@ -105,8 +105,9 @@
       "endCaptures": { "0": { "name": "punctuation.definition.string.end.cmake" } }
     },
     "generatorExpression": {
+      "comment": "Do not start a generator expression at escaped $< sequences, such as CMake regex patterns matching a literal generator expression prefix.",
       "name": "meta.generator-expression.cmake",
-      "begin": "\\$<",
+      "begin": "(?<!\\\\)\\$<",
       "beginCaptures": { "0": { "name": "punctuation.definition.generator-expression.begin.cmake" } },
       "end": ">",
       "endCaptures": { "0": { "name": "punctuation.definition.generator-expression.end.cmake" } },
@@ -412,4 +413,4 @@
       "match": "\\b(?i:return)\\b"
     }
   }
-}
+}

test/visual-syntax-test/CMakeLists.txt

@@ -49,6 +49,16 @@ if(${CMAKE_VERSION} VERSION_GREATER_EQUAL "3.20")
   message(STATUS "CMake 3.20+")
 endif()
 
+# Issue #5028: Fix highlighting of escaped $< in CMake regex strings
+function(validate_configure_path value description)
+  if("${value}" MATCHES "\\$<")
+    message(FATAL_ERROR
+      "${description} must be known at configure time; generator expressions "
+      "are not supported."
+    )
+  endif()
+endfunction()
+
 if(CMAKE_SYSTEM_NAME STREQUAL "Linux")
   message(STATUS "Linux")
 elseif(CMAKE_SYSTEM_NAME STREQUAL "Windows")
@@ -471,4 +481,4 @@ set_target_properties(MyLib PROPERTIES
   SOURCES "lib.cpp"
   COMPILE_DEFINITIONS_DEBUG "DEBUG=1"
   LINK_FLAGS_RELEASE "/OPT:REF"
-)
+)