Improve configure2cmake to find_package only in certain conditions

It doesn't make much sense to look for X11 related packages on
macOS and Windows by default. Usually they would not be there, and
as a result the configuration step would show a long list of scary
not found packages, and also eat precious configure time.

Change the conversion script to allow putting conditions around
generated find_package calls.

These conditions can be manually set in the conversion script
library mapping, using the emit_if argument,
which we do for the X11 and Wayland related packages.

They are also computed by checking which features use a given library,
and if the feature is protected by a simple emitIf condition like
config.linux, the relevant library find_package call will be protected
by the same condition.

If a developer still wishes to look for all packages, they can define
the CACHE variable QT_FIND_ALL_PACKAGES_ALWAYS to ON.

The relevant configure.cmake files are regenerated in this patch.

Change-Id: I6f918a94f50257ec41d6216305dae9774933389a
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

2 files changed, 57 insertions, 6 deletions

diff --git a/util/cmake/configurejson2cmake.py b/util/cmake/configurejson2cmake.py
index 040e8ee7b4..d1646ed082 100755
--- a/util/cmake/configurejson2cmake.py
+++ b/util/cmake/configurejson2cmake.py
@@ -181,9 +181,29 @@ def parseLib(ctx, lib, data, cm_fh, cmake_find_packages_set):
     if newlib.targetName in cmake_find_packages_set:
         return
 
+    # If certain libraries are used within a feature, but the feature
+    # is only emitted conditionally with a simple condition (like
+    # 'on Windows' or 'on Linux'), we should enclose the find_package
+    # call for the library into the same condition.
+    emit_if = newlib.emit_if
+
+    # Only look through features if a custom emit_if wasn't provided.
+    if not emit_if:
+        for feature in data['features']:
+            feature_data = data['features'][feature]
+            if 'condition' in feature_data and \
+                    'libs.{}'.format(lib) in feature_data['condition'] and \
+                    'emitIf' in feature_data and \
+                    'config.' in feature_data['emitIf']:
+                emit_if = feature_data['emitIf']
+                break
+
+    if emit_if:
+        emit_if = map_condition(emit_if)
+
     cmake_find_packages_set.add(newlib.targetName)
 
-    cm_fh.write(generate_find_package_info(newlib))
+    cm_fh.write(generate_find_package_info(newlib, emit_if=emit_if))
 
 
 def lineify(label, value, quote=True):
@@ -890,7 +910,7 @@ def processLibraries(ctx, data, cm_fh):
         return
 
     for lib in data['libraries']:
-        parseLib(ctx, lib, data['libraries'][lib], cm_fh, cmake_find_packages_set)
+        parseLib(ctx, lib, data, cm_fh, cmake_find_packages_set)
 
 
 def processSubconfigs(dir, ctx, data):
diff --git a/util/cmake/helper.py b/util/cmake/helper.py
index ee4274abd7..d9e9fd16e3 100644
--- a/util/cmake/helper.py
+++ b/util/cmake/helper.py
@@ -35,7 +35,8 @@ class LibraryMapping:
                  targetName: typing.Optional[str], *,
                  resultVariable: typing.Optional[str] = None,
                  extra: typing.List[str] = [],
-                 appendFoundSuffix: bool = True) -> None:
+                 appendFoundSuffix: bool = True,
+                 emit_if: str = '') -> None:
         self.soName = soName
         self.packageName = packageName
         self.resultVariable = resultVariable
@@ -43,6 +44,10 @@ class LibraryMapping:
         self.extra = extra
         self.targetName = targetName
 
+        # if emit_if is non-empty, the generated find_package call
+        # for a library will be surrounded by this condition.
+        self.emit_if = emit_if
+
     def is_qt(self) -> bool:
         return self.packageName == 'Qt' \
             or self.packageName == 'Qt5' \
@@ -172,6 +177,7 @@ _qt_library_map = [
     # qtzlib: No longer supported.
 ]
 
+# Note that the library map is adjusted dynamically further down.
 _library_map = [
     # 3rd party:
     LibraryMapping('atspi', 'ATSPI2', 'PkgConfig::ATSPI2'),
@@ -247,6 +253,20 @@ _library_map = [
 ]
 
 
+def _adjust_library_map():
+    # Assign a Linux condition on all x and wayland related packages.
+    # We don't want to get pages of package not found messages on
+    # Windows and macOS, and this also improves configure time on
+    # those platforms.
+    linux_package_prefixes = ['xcb', 'x11', 'xkb', 'xrender', 'xlib', 'wayland']
+    for i, _ in enumerate(_library_map):
+        if any([_library_map[i].soName.startswith(p) for p in linux_package_prefixes]):
+            _library_map[i].emit_if = 'config.linux'
+
+
+_adjust_library_map()
+
+
 def find_3rd_party_library_mapping(soName: str) -> typing.Optional[LibraryMapping]:
     for i in _library_map:
         if i.soName == soName:
@@ -356,8 +376,10 @@ def map_3rd_party_library(lib: str) -> str:
     return mapping.targetName + libpostfix
 
 
-def generate_find_package_info(lib: LibraryMapping, use_qt_find_package: bool=True, *,
-                               indent: int = 0) -> str:
+def generate_find_package_info(lib: LibraryMapping,
+                               use_qt_find_package: bool=True, *,
+                               indent: int = 0,
+                               emit_if: str = '') -> str:
     isRequired = False
 
     extra = lib.extra.copy()
@@ -377,7 +399,8 @@ def generate_find_package_info(lib: LibraryMapping, use_qt_find_package: bool=Tr
         extra += ['PROVIDED_TARGETS', cmake_target_name]
 
     result = ''
-    ind = '    ' * indent
+    one_ind = '    '
+    ind = one_ind * indent
 
     if use_qt_find_package:
         if extra:
@@ -393,4 +416,12 @@ def generate_find_package_info(lib: LibraryMapping, use_qt_find_package: bool=Tr
         else:
             result = '{}find_package({})\n'.format(ind, lib.packageName)
 
+    # If a package should be found only in certain conditions, wrap
+    # the find_package call within that condition.
+    if emit_if:
+        result = "if(({emit_if}) OR QT_FIND_ALL_PACKAGES_ALWAYS)\n" \
+                 "{ind}{result}endif()\n".format(emit_if=emit_if,
+                                                 result=result,
+                                                 ind=one_ind)
+
     return result