From 1b873579671a152edca021f69bc2e4b39f8b69ad Mon Sep 17 00:00:00 2001
From: Viktor Szakats <commit@vsz.me>
Date: Fri, 14 Feb 2025 11:35:12 +0100
Subject: [PATCH] cmake: allow empty custom `IMPORT_LIB_SUFFIX`, add suffix
 collision detection

Allow overriding the `IMPORT_LIB_SUFFIX` default with an empty value.

Also:
- add a fatal error if the implib and static lib filename are identical.
- clarify `IMPORT_LIB_SUFFIX` default value in the documentation.

Reported-by: RubisetCie on Github
Fixes #16324
Ref: 1199308dbc902c52be67fc805c72dd2582520d30 #11505

Closes #16332
---
 docs/INSTALL-CMAKE.md |  2 +-
 lib/CMakeLists.txt    | 23 ++++++++++++++++-------
 2 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/docs/INSTALL-CMAKE.md b/docs/INSTALL-CMAKE.md
index 893f4b57f8..8f19c51cc9 100644
--- a/docs/INSTALL-CMAKE.md
+++ b/docs/INSTALL-CMAKE.md
@@ -167,7 +167,7 @@ assumes that CMake generates `Makefile`:
 - `ENABLE_CURLDEBUG`:                       Enable TrackMemory debug feature. Default: =`ENABLE_DEBUG`
 - `ENABLE_CURL_MANUAL`:                     Build the man page for curl and enable its `-M`/`--manual` option. Default: `ON`
 - `ENABLE_DEBUG`:                           Enable curl debug features (for developing curl itself). Default: `OFF`
-- `IMPORT_LIB_SUFFIX`:                      Import library suffix. Default: `_imp`
+- `IMPORT_LIB_SUFFIX`:                      Import library suffix. Default: `_imp` for MSVC-like toolchains, otherwise empty.
 - `LIBCURL_OUTPUT_NAME`:                    Basename of the curl library. Default: `libcurl`
 - `PICKY_COMPILER`:                         Enable picky compiler options. Default: `ON`
 - `STATIC_LIB_SUFFIX`:                      Static library suffix. Default: (empty)
diff --git a/lib/CMakeLists.txt b/lib/CMakeLists.txt
index 5f1b395f0a..12f5a1936b 100644
--- a/lib/CMakeLists.txt
+++ b/lib/CMakeLists.txt
@@ -69,18 +69,27 @@ endif()
 ## Library definition
 
 if(NOT DEFINED IMPORT_LIB_SUFFIX)
-  set(IMPORT_LIB_SUFFIX "")
+  # Suffix implib name with "_imp" by default, to avoid conflicting with
+  # the generated static "libcurl.lib" (typically with MSVC).
+  if(WIN32 AND BUILD_SHARED_LIBS AND
+     CMAKE_IMPORT_LIBRARY_SUFFIX STREQUAL CMAKE_STATIC_LIBRARY_SUFFIX)
+    set(IMPORT_LIB_SUFFIX "_imp")
+  else()
+    set(IMPORT_LIB_SUFFIX "")
+  endif()
 endif()
 if(NOT DEFINED STATIC_LIB_SUFFIX)
   set(STATIC_LIB_SUFFIX "")
 endif()
 
-# Add "_imp" as a suffix before the extension to avoid conflicting with
-# the statically linked "libcurl.lib" (typically with MSVC)
-if(WIN32 AND
-   NOT IMPORT_LIB_SUFFIX AND
-   CMAKE_STATIC_LIBRARY_SUFFIX STREQUAL CMAKE_IMPORT_LIBRARY_SUFFIX)
-  set(IMPORT_LIB_SUFFIX "_imp")
+# Detect implib static lib filename collision
+if(WIN32 AND BUILD_STATIC_LIBS AND BUILD_SHARED_LIBS AND
+   "${IMPORT_LIB_SUFFIX}${CMAKE_IMPORT_LIBRARY_SUFFIX}" STREQUAL
+   "${STATIC_LIB_SUFFIX}${CMAKE_STATIC_LIBRARY_SUFFIX}")
+  message(FATAL_ERROR "Library suffix is the same ('${STATIC_LIB_SUFFIX}${CMAKE_STATIC_LIBRARY_SUFFIX}') "
+    "for the import and static '${LIBCURL_OUTPUT_NAME}' library. "
+    "Set IMPORT_LIB_SUFFIX and/or STATIC_LIB_SUFFIX to different values, "
+    "or disable building either the shared or static library to avoid the filename collision.")
 endif()
 
 # Whether to do a single compilation pass for libcurl sources and reuse these
-- 
2.47.3