qt: Allow specifying separate tools for qt4/5/6

Currently you can only use one of qt4, qt5, qt6 in a single project
when using a machine file because the config-tool lookup for qt only
looks at `qmake` in the machine files, instead of looking up the
binary names directly.

Allow specifying `qmake` `qmake4` `qmake5` and `qmake6`.

This is necessary for gstreamer, which can build separate qt5 and qt6
plugins that are distributed as static libraries, so the user can pick
which one to use.

mesonbuild/dependencies/qt.py

@@ -252,11 +252,11 @@ class QmakeQtDependency(_QtBase, ConfigToolDependency, metaclass=abc.ABCMeta):
 
     """Find Qt using Qmake as a config-tool."""
 
-    tool_name = 'qmake'
     version_arg = '-v'
 
     def __init__(self, name: str, env: 'Environment', kwargs: T.Dict[str, T.Any]):
         _QtBase.__init__(self, name, kwargs)
+        self.tool_name = f'qmake{self.qtver}'
         self.tools = [f'qmake{self.qtver}', f'qmake-{self.name}', 'qmake']
 
         # Add additional constraints that the Qt version is met, but preserve

mesonbuild/programs.py

@@ -26,7 +26,7 @@ from pathlib import Path
 
 from . import mesonlib
 from . import mlog
-from .mesonlib import MachineChoice
+from .mesonlib import MachineChoice, OrderedSet
 
 if T.TYPE_CHECKING:
     from .environment import Environment
@@ -355,15 +355,18 @@ def find_external_program(env: 'Environment', for_machine: MachineChoice, name:
                           display_name: str, default_names: T.List[str],
                           allow_default_for_cross: bool = True) -> T.Generator['ExternalProgram', None, None]:
     """Find an external program, checking the cross file plus any default options."""
+    potential_names = OrderedSet(default_names)
+    potential_names.add(name)
     # Lookup in cross or machine file.
-    potential_cmd = env.lookup_binary_entry(for_machine, name)
-    if potential_cmd is not None:
-        mlog.debug(f'{display_name} binary for {for_machine} specified from cross file, native file, '
-                   f'or env var as {potential_cmd}')
-        yield ExternalProgram.from_entry(name, potential_cmd)
-        # We never fallback if the user-specified option is no good, so
-        # stop returning options.
-        return
+    for potential_name in potential_names:
+        potential_cmd = env.lookup_binary_entry(for_machine, potential_name)
+        if potential_cmd is not None:
+            mlog.debug(f'{display_name} binary for {for_machine} specified from cross file, native file, '
+                       f'or env var as {potential_cmd}')
+            yield ExternalProgram.from_entry(potential_name, potential_cmd)
+            # We never fallback if the user-specified option is no good, so
+            # stop returning options.
+            return
     mlog.debug(f'{display_name} binary missing from cross or native file, or env var undefined.')
     # Fallback on hard-coded defaults, if a default binary is allowed for use
     # with cross targets, or if this is not a cross target

test cases/frameworks/4 qt/meson.build

@@ -152,7 +152,8 @@ foreach qt : ['qt4', 'qt5', 'qt6']
     endif
 
     # Check we can apply a version constraint
-    dependency(qt, modules: qt_modules, version: '>=@0@'.format(qtdep.version()), method : get_option('method'))
+    accept_versions = ['>=@0@'.format(qtdep.version()), '<@0@'.format(qtdep.version()[0].to_int() + 1)]
+    dependency(qt, modules: qt_modules, version: accept_versions, method : get_option('method'))
 
   endif
 endforeach