Use CompilerArgs for generation of compile commands

At the same time, also fix the order in which compile arguments are
added. Detailed comments have been added concerning the priority and
order of the arguments.

Also adds a unit test and an integration test for the same.

1 files changed, 39 insertions, 11 deletions

diff --git a/mesonbuild/backend/backends.py b/mesonbuild/backend/backends.py
index eadc8cc..a83d95f 100644
--- a/mesonbuild/backend/backends.py
+++ b/mesonbuild/backend/backends.py
@@ -21,6 +21,7 @@ from .. import compilers
 import json
 import subprocess
 from ..mesonlib import MesonException, get_compiler_for_source, classify_unity_sources
+from ..compilers import CompilerArgs
 
 class CleanTrees:
     '''
@@ -338,32 +339,59 @@ class Backend:
         return extra_args
 
     def generate_basic_compiler_args(self, target, compiler, no_warn_args=False):
-        commands = []
+        # Create an empty commands list, and start adding arguments from
+        # various sources in the order in which they must override each other
+        # starting from hard-coded defaults followed by build options and so on.
+        commands = CompilerArgs(compiler)
+        # First, the trivial ones that are impossible to override.
+        #
+        # Add -nostdinc/-nostdinc++ if needed; can't be overriden
         commands += self.get_cross_stdlib_args(target, compiler)
+        # Add things like /NOLOGO or -pipe; usually can't be overriden
         commands += compiler.get_always_args()
+        # Only add warning-flags by default if the buildtype enables it, and if
+        # we weren't explicitly asked to not emit warnings (for Vala, f.ex)
         if no_warn_args:
             commands += compiler.get_no_warn_args()
         elif self.environment.coredata.get_builtin_option('buildtype') != 'plain':
             commands += compiler.get_warn_args(self.environment.coredata.get_builtin_option('warning_level'))
+        # Add -Werror if werror=true is set in the build options set on the
+        # command-line or default_options inside project(). This only sets the
+        # action to be done for warnings if/when they are emitted, so it's ok
+        # to set it after get_no_warn_args() or get_warn_args().
+        if self.environment.coredata.get_builtin_option('werror'):
+            commands += compiler.get_werror_args()
+        # Add compile args for c_* or cpp_* build options set on the
+        # command-line or default_options inside project().
         commands += compiler.get_option_compile_args(self.environment.coredata.compiler_options)
-        commands += self.build.get_global_args(compiler)
+        # Add buildtype args: optimization level, debugging, etc.
+        commands += compiler.get_buildtype_args(self.environment.coredata.get_builtin_option('buildtype'))
+        # Add compile args added using add_project_arguments()
         commands += self.build.get_project_args(compiler, target.subproject)
+        # Add compile args added using add_global_arguments()
+        # These override per-project arguments
+        commands += self.build.get_global_args(compiler)
+        # Compile args added from the env: CFLAGS/CXXFLAGS, etc. We want these
+        # to override all the defaults, but not the per-target compile args.
         commands += self.environment.coredata.external_args[compiler.get_language()]
-        commands += self.escape_extra_args(compiler, target.get_extra_args(compiler.get_language()))
-        commands += compiler.get_buildtype_args(self.environment.coredata.get_builtin_option('buildtype'))
-        if self.environment.coredata.get_builtin_option('werror'):
-            commands += compiler.get_werror_args()
+        # Always set -fPIC for shared libraries
         if isinstance(target, build.SharedLibrary):
             commands += compiler.get_pic_args()
+        # Set -fPIC for static libraries by default unless explicitly disabled
         if isinstance(target, build.StaticLibrary) and target.pic:
             commands += compiler.get_pic_args()
+        # Add compile args needed to find external dependencies
+        # Link args are added while generating the link command
         for dep in target.get_external_deps():
-            # Cflags required by external deps might have UNIX-specific flags,
-            # so filter them out if needed
-            commands += compiler.unix_args_to_native(dep.get_compile_args())
+            commands += dep.get_compile_args()
+            # Qt needs -fPIC for executables
+            # XXX: We should move to -fPIC for all executables
             if isinstance(target, build.Executable):
-                commands += dep.get_exe_args()
-
+                commands += dep.get_exe_args(compiler)
+            # For 'automagic' deps: Boost and GTest. Also dependency('threads').
+            # pkg-config puts the thread flags itself via `Cflags:`
+            if dep.need_threads():
+                commands += compiler.thread_flags()
         # Fortran requires extra include directives.
         if compiler.language == 'fortran':
             for lt in target.link_targets: