FindBrotli cleanup & fixes (#1786)

* Unimportant cleanup of FindBrotli

Some whitespace, removal of an unused var, and add a comment about
the missing version support

* Fix incorrect var in FindBrotli

Not much to say, it was just the wrong one. Not sure how that happened,
maybe a holdover from when I did an overhaul at some point..

* Tiny useless edit to FindBrotli

Just a little tweak to how I was postfixing those -static strings to the
lib names. Mostly pointless..

* Simplify some FindBrotli code

Nothing much, just reducing redundant stuff & a cleanup of a comment.

* Ignore PkgConf in FindBrotli if looking for static

As per the issue mentioned in this comment, static PkgConf support
is broken upstream. After testing, I found it'll just accept shared
even if you try to find static, so I'm merely disabling that feature
for this FindBrotli module.

That said, you can still get the static libs if you have them installed,
but PkgConf will be ignored even if found in favor of a regular
find_library call. Otherwise you'd end up with shared libs even if you
ask for static (with PkgConf installed).

TLDR: actually fail correctly when static libs aren't found when PkgConf
thought they were.

cmake/FindBrotli.cmake

@@ -1,6 +1,6 @@
 # A simple FindBrotli package for Cmake's find_package function.
 # Note: This find package doesn't have version support, as the version file doesn't seem to be installed on most systems.
-# 
+#
 # If you want to find the static packages instead of shared (the default), define BROTLI_USE_STATIC_LIBS as TRUE.
 # The targets will have the same names, but it will use the static libs.
 #
@@ -14,7 +14,7 @@
 
 # If they asked for a specific version, warn/fail since we don't support it.
 # TODO: if they start distributing the version somewhere, implement finding it.
-# But currently there's a version header that doesn't seem to get installed.
+# See https://github.com/google/brotli/issues/773#issuecomment-579133187
 if(Brotli_FIND_VERSION)
 	set(_brotli_version_error_msg "FindBrotli.cmake doesn't have version support!")
 	# If the package is required, throw a fatal error
@@ -68,29 +68,24 @@ if(BROTLI_USE_STATIC_LIBS)
 	set(_brotli_stat_str "_STATIC")
 endif()
 
-# Lets us know we are using the PkgConfig libraries
-# Will be set false if any non-pkgconf vars are used
-set(_brotli_using_pkgconf TRUE)
-
 # Each string here is "ComponentName;LiteralName" (the semi-colon is a delimiter)
 foreach(_listvar "common;common" "decoder;dec" "encoder;enc")
 	# Split the component name and literal library name from the listvar
 	list(GET _listvar 0 _component_name)
 	list(GET _listvar 1 _libname)
 
-	if(PKG_CONFIG_FOUND)
+	# NOTE: We can't rely on PkgConf for static libs since the upstream static lib support is broken
+	# See https://github.com/google/brotli/issues/795
+	# TODO: whenever their issue is fixed upstream, remove this "AND NOT BROTLI_USE_STATIC_LIBS" check
+	if(PKG_CONFIG_FOUND AND NOT BROTLI_USE_STATIC_LIBS)
 		# These need to be GLOBAL for MinGW when making ALIAS libraries against them.
-		if(BROTLI_USE_STATIC_LIBS)
-			# Have to use _STATIC to tell PkgConfig to find the static libs.
-			pkg_check_modules(Brotli_${_component_name}_STATIC QUIET GLOBAL IMPORTED_TARGET libbrotli${_libname})
-		else()
-			pkg_check_modules(Brotli_${_component_name} QUIET GLOBAL IMPORTED_TARGET libbrotli${_libname})
-		endif()
+		# Have to postfix _STATIC on the name to tell PkgConfig to find the static libs.
+		pkg_check_modules(Brotli_${_component_name}${_brotli_stat_str} QUIET GLOBAL IMPORTED_TARGET libbrotli${_libname})
 	endif()
 
-	# Check if the target was already found by Pkgconf 
-	if(TARGET PkgConfig::Brotli_${_component_name} OR TARGET PkgConfig::Brotli_${_component_name}_STATIC)
-		# Can't use generators for ALIAS targets, so you get this jank
+	# Check if the target was already found by Pkgconf
+	if(TARGET PkgConfig::Brotli_${_component_name}${_brotli_stat_str})
+		# ALIAS since we don't want the PkgConfig namespace on the Cmake library (for end-users)
 		add_library(Brotli::${_component_name} ALIAS PkgConfig::Brotli_${_component_name}${_brotli_stat_str})
 
 		# Tells HANDLE_COMPONENTS we found the component
@@ -109,23 +104,18 @@ foreach(_listvar "common;common" "decoder;dec" "encoder;enc")
 		continue()
 	endif()
 
-	# Lets us know we aren't using the PkgConfig libraries
-	set(_brotli_using_pkgconf FALSE)
 	if(Brotli_FIND_REQUIRED_${_component_name})
 		# If it's required, we can set the name used in find_library as a required var for FindPackageHandleStandardArgs
 		list(APPEND _brotli_req_vars "Brotli_${_component_name}")
 	endif()
 
+	list(APPEND _brotli_lib_names
+		"brotli${_libname}"
+		"libbrotli${_libname}"
+	)
 	if(BROTLI_USE_STATIC_LIBS)
-		list(APPEND _brotli_lib_names
-			"brotli${_libname}-static"
-			"libbrotli${_libname}-static"
-		)
-	else()
-		list(APPEND _brotli_lib_names
-			"brotli${_libname}"
-			"libbrotli${_libname}"
-		)
+		# Postfix "-static" to the libnames since we're looking for static libs
+		list(TRANSFORM _brotli_lib_names APPEND "-static")
 	endif()
 
 	find_library(Brotli_${_component_name}
@@ -168,7 +158,7 @@ find_package_handle_standard_args(Brotli
 		Brotli_FOUND
 	REQUIRED_VARS
 		Brotli_INCLUDE_DIR
-		${_brotli_required_targets}
+		${_brotli_req_vars}
 	HANDLE_COMPONENTS
 )