build: add Source Link to embed GitHub source mappings in PDBs (#40055)

* build: add Source Link to embed GitHub source mappings in PDBs

* Gate Source Link on pipeline builds only

Only generate sourcelink.json and pass /SOURCELINK to the linker when
PIPELINE_BUILD_ID is defined (i.e. during CI pipeline builds). This
avoids unnecessary Source Link artifacts in local developer builds.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Ben Hillis <benhill@ntdev.microsoft.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: 3 people

CMakeLists.txt

@@ -156,6 +156,12 @@ file(MAKE_DIRECTORY ${BIN})
 set (GENERATED_DIR ${CMAKE_BINARY_DIR}/generated)
 file(MAKE_DIRECTORY ${GENERATED_DIR})
 
+# Generate Source Link JSON so debuggers can fetch source from GitHub (pipeline builds only)
+if (DEFINED PIPELINE_BUILD_ID)
+    set(SOURCELINK_JSON "${GENERATED_DIR}/sourcelink.json")
+    file(WRITE "${SOURCELINK_JSON}" "{\"documents\":{\"${CMAKE_SOURCE_DIR}/*\":\"https://raw.githubusercontent.com/microsoft/WSL/${COMMIT_HASH}/*\"}}")
+endif()
+
 set(PACKAGE_CERTIFICATE ${GENERATED_DIR}/dev-cert.pfx)
 file(CREATE_LINK ${WSLG_SOURCE_DIR}/${TARGET_PLATFORM}/${WSLG_TS_PLUGIN_DLL} ${BIN}/${WSLG_TS_PLUGIN_DLL})
 file(CREATE_LINK ${WSLDEPS_SOURCE_DIR}/bin/wsldeps.dll ${BIN}/wsldeps.dll)
@@ -234,6 +240,10 @@ set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} /Zi /guard:cf /Qspectre"
 # Linker flags
 set(CMAKE_SHARED_LINKER_FLAGS_RELEASE "${CMAKE_SHARED_LINKER_FLAGS_RELEASE} /debug:full /debugtype:cv,fixup /guard:cf /DYNAMICBASE")
 set(CMAKE_EXE_LINKER_FLAGS_RELEASE "${CMAKE_EXE_LINKER_FLAGS_RELEASE} /debug:full /debugtype:cv,fixup /guard:cf /DYNAMICBASE")
+if (DEFINED SOURCELINK_JSON)
+    set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} /SOURCELINK:\"${SOURCELINK_JSON}\"")
+    set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} /SOURCELINK:\"${SOURCELINK_JSON}\"")
+endif()
 if (${TARGET_PLATFORM} STREQUAL "x64")
     set(CMAKE_SHARED_LINKER_FLAGS_RELEASE "${CMAKE_SHARED_LINKER_FLAGS_RELEASE} /CETCOMPAT")
     set(CMAKE_EXE_LINKER_FLAGS_RELEASE "${CMAKE_EXE_LINKER_FLAGS_RELEASE} /CETCOMPAT")