Add a helper for fetching of binaries from cross files

A number of cases have to be taken care of while doing this, so
refactor it into a helper on ExternalProgram and use it everywhere.

1. Command is a list of len > 1, use it as-is
2. Command is a list of len == 1 (or a string), use as a string
3. If command is an absolute path, use it as-is
4. If command is not an absolute path, search for it

2 files changed, 22 insertions, 5 deletions

diff --git a/mesonbuild/dependencies/base.py b/mesonbuild/dependencies/base.py
index 8319cb7..07d06a1 100644
--- a/mesonbuild/dependencies/base.py
+++ b/mesonbuild/dependencies/base.py
@@ -438,8 +438,7 @@ class PkgConfigDependency(ExternalDependency):
                 if self.required:
                     raise DependencyException('Pkg-config binary missing from cross file')
             else:
-                pkgname = environment.cross_info.config['binaries']['pkgconfig']
-                potential_pkgbin = ExternalProgram(pkgname, silent=True)
+                potential_pkgbin = ExternalProgram.from_cross_info(environment.cross_info, 'pkgconfig')
                 if potential_pkgbin.found():
                     self.pkgbin = potential_pkgbin
                     PkgConfigDependency.class_pkgbin = self.pkgbin
@@ -799,6 +798,24 @@ class ExternalProgram:
         return r.format(self.__class__.__name__, self.name, self.command)
 
     @staticmethod
+    def from_cross_info(cross_info, name):
+        if name not in cross_info.config['binaries']:
+            return NonExistingExternalProgram()
+        command = cross_info.config['binaries'][name]
+        if not isinstance(command, (list, str)):
+            raise MesonException('Invalid type {!r} for binary {!r} in cross file'
+                                 ''.format(command, name))
+        if isinstance(command, list):
+            if len(command) == 1:
+                command = command[0]
+        # We cannot do any searching if the command is a list, and we don't
+        # need to search if the path is an absolute path.
+        if isinstance(command, list) or os.path.isabs(command):
+            return ExternalProgram(name, command=command, silent=True)
+        # Search for the command using the specified string!
+        return ExternalProgram(command, silent=True)
+
+    @staticmethod
     def _shebang_to_cmd(script):
         """
         Check if the file has a shebang and manually parse it to figure out
diff --git a/mesonbuild/dependencies/ui.py b/mesonbuild/dependencies/ui.py
index 72958dd..324f9fa 100644
--- a/mesonbuild/dependencies/ui.py
+++ b/mesonbuild/dependencies/ui.py
@@ -291,10 +291,10 @@ class QtBaseDependency(ExternalDependency):
                 self.bindir = os.path.join(prefix, 'bin')
 
     def _find_qmake(self, qmake):
-        # Even when cross-compiling, if we don't get a cross-info qmake, we
+        # Even when cross-compiling, if a cross-info qmake is not specified, we
         # fallback to using the qmake in PATH because that's what we used to do
-        if self.env.is_cross_build():
-            qmake = self.env.cross_info.config['binaries'].get('qmake', qmake)
+        if self.env.is_cross_build() and 'qmake' in self.env.cross_info.config['binaries']:
+            return ExternalProgram.from_cross_info(self.env.cross_info, 'qmake')
         return ExternalProgram(qmake, silent=True)
 
     def _qmake_detect(self, mods, kwargs):