vala: Add support for cross-compilation.

It is very useful to be able to pass -DFOO and do #if FOO in Vala code,
for the few cases where platform-dependent Vala code is needed.

Fixes mesonbuild#1771

mesonbuild/backend/ninjabackend.py

@@ -1294,8 +1294,12 @@ def generate_vala_compile(self, target, outfile):
         dependency_vapis = self.determine_dep_vapis(target)
         extra_dep_files += dependency_vapis
         args += extra_args
+        if target.is_cross:
+            crstr = '_CROSS'
+        else:
+            crstr = ''
         element = NinjaBuildElement(self.all_outputs, valac_outputs,
-                                    valac.get_language() + '_COMPILER',
+                                    '%s%s_COMPILER' % (valac.get_language(), crstr),
                                     all_files + dependency_vapis)
         element.add_item('ARGS', args)
         element.add_dep(extra_dep_files)
@@ -1661,9 +1665,14 @@ def generate_cs_compile_rule(self, compiler, outfile):
         outfile.write(description)
         outfile.write('\n')
 
-    def generate_vala_compile_rules(self, compiler, outfile):
-        rule = 'rule %s_COMPILER\n' % compiler.get_language()
-        invoc = ' '.join([ninja_quote(i) for i in compiler.get_exelist()])
+    def generate_vala_compile_rules(self, compiler, is_cross, outfile):
+        if is_cross:
+            crstr = '_CROSS'
+        else:
+            crstr = ''
+        rule = 'rule %s%s_COMPILER\n' % (compiler.get_language(), crstr)
+        cross_args = self.get_cross_info_lang_args('vala', is_cross)
+        invoc = ' '.join([ninja_quote(i) for i in compiler.get_exelist() + cross_args])
         command = ' command = %s $ARGS $in\n' % invoc
         description = ' description = Compiling Vala source $in.\n'
         restat = ' restat = 1\n' # ValaC does this always to take advantage of it.
@@ -1764,8 +1773,7 @@ def generate_compile_rule_for(self, langname, compiler, is_cross, outfile):
                 self.generate_cs_compile_rule(compiler, outfile)
             return
         if langname == 'vala':
-            if not is_cross:
-                self.generate_vala_compile_rules(compiler, outfile)
+            self.generate_vala_compile_rules(compiler, is_cross, outfile)
             return
         if langname == 'rust':
             self.generate_rust_compile_rules(compiler, outfile, is_cross)

mesonbuild/compilers/vala.py

@@ -20,12 +20,12 @@
 from .compilers import Compiler
 
 class ValaCompiler(Compiler):
-    def __init__(self, exelist, version):
+    def __init__(self, exelist, version, is_cross):
         self.language = 'vala'
         super().__init__(exelist, version)
         self.version = version
         self.id = 'valac'
-        self.is_cross = False
+        self.is_cross = is_cross
         self.base_options = ['b_colorout']
 
     def name_string(self):

mesonbuild/environment.py

@@ -331,6 +331,7 @@ def __init__(self, source_dir, build_dir, options):
         self.default_objc = ['cc']
         self.default_objcpp = ['c++']
         self.default_fortran = ['gfortran', 'g95', 'f95', 'f90', 'f77', 'ifort']
+        self.default_vala = ['valac']
         self.default_rust = ['rustc']
         self.default_static_linker = ['ar']
         self.vs_static_linker = ['lib']
@@ -771,19 +772,25 @@ def detect_cs_compiler(self):
 
         self._handle_exceptions(popen_exceptions, compilers)
 
-    def detect_vala_compiler(self):
-        if 'VALAC' in os.environ:
-            exelist = shlex.split(os.environ['VALAC'])
-        else:
-            exelist = ['valac']
-        try:
-            p, out = Popen_safe(exelist + ['--version'])[0:2]
-        except OSError:
-            raise EnvironmentException('Could not execute Vala compiler "%s"' % ' '.join(exelist))
-        version = search_version(out)
-        if 'Vala' in out:
-            return ValaCompiler(exelist, version)
-        raise EnvironmentException('Unknown compiler "' + ' '.join(exelist) + '"')
+    def detect_vala_compiler(self, want_cross):
+        popen_exceptions = {}
+        compilers, ccache, is_cross, exe_wrap = self._get_compilers('vala', 'VALAC', want_cross)
+        for compiler in compilers:
+            if isinstance(compiler, str):
+                compiler = [compiler]
+            arg = ['--version']
+            try:
+                p, out = Popen_safe(compiler + arg)[0:2]
+            except OSError as e:
+                popen_exceptions[' '.join(compiler + arg)] = e
+                continue
+
+            version = search_version(out)
+
+            if 'Vala' in out:
+                return ValaCompiler(compiler, version, is_cross)
+
+        self._handle_exceptions(popen_exceptions, compilers)
 
     def detect_rust_compiler(self, want_cross):
         popen_exceptions = {}

mesonbuild/interpreter.py

@@ -2578,9 +2578,9 @@ def detect_compilers(self, lang, need_cross_compiler):
             if need_cross_compiler:
                 cross_comp = comp  # C# is platform independent.
         elif lang == 'vala':
-            comp = self.environment.detect_vala_compiler()
+            comp = self.environment.detect_vala_compiler(False)
             if need_cross_compiler:
-                cross_comp = comp  # Vala compiles to platform-independent C
+                cross_comp = self.environment.detect_vala_compiler(True)
         elif lang == 'd':
             comp = self.environment.detect_d_compiler(False)
             if need_cross_compiler: