preprocess: Allow custom_tgt, custom_idx and generated_list

It was documented to be supported but only File and str were actually
working.

mesonbuild/build.py

@@ -2609,9 +2609,10 @@ class CompileTarget(BuildTarget):
                  subdir: str,
                  subproject: str,
                  environment: environment.Environment,
-                 sources: T.List[File],
+                 sources: T.List['SourceOutputs'],
                  output_templ: str,
                  compiler: Compiler,
+                 backend: Backend,
                  kwargs):
         compilers = {compiler.get_language(): compiler}
         super().__init__(name, subdir, subproject, compiler.for_machine,
@@ -2620,11 +2621,13 @@ class CompileTarget(BuildTarget):
         self.compiler = compiler
         self.output_templ = output_templ
         self.outputs = []
-        for f in sources:
-            plainname = os.path.basename(f.fname)
-            basename = os.path.splitext(plainname)[0]
-            self.outputs.append(output_templ.replace('@BASENAME@', basename).replace('@PLAINNAME@', plainname))
-        self.sources_map = dict(zip(sources, self.outputs))
+        self.sources_map: T.Dict[File, str] = {}
+        for f in self.sources:
+            self._add_output(f)
+        for gensrc in self.generated:
+            for s in gensrc.get_outputs():
+                rel_src = backend.get_target_generated_dir(self, gensrc, s)
+                self._add_output(File.from_built_relative(rel_src))
 
     def type_suffix(self) -> str:
         return "@compile"
@@ -2633,6 +2636,13 @@ class CompileTarget(BuildTarget):
     def is_unity(self) -> bool:
         return False
 
+    def _add_output(self, f: File) -> None:
+        plainname = os.path.basename(f.fname)
+        basename = os.path.splitext(plainname)[0]
+        o = self.output_templ.replace('@BASENAME@', basename).replace('@PLAINNAME@', plainname)
+        self.outputs.append(o)
+        self.sources_map[f] = o
+
 
 class RunTarget(Target, CommandBase):
 

mesonbuild/interpreter/compiler.py

@@ -6,6 +6,7 @@ from __future__ import annotations
 import enum
 import functools
 import os
+import itertools
 import typing as T
 
 from .. import build
@@ -28,6 +29,7 @@ if T.TYPE_CHECKING:
     from ..compilers import Compiler, RunResult
     from ..interpreterbase import TYPE_var, TYPE_kwargs
     from .kwargs import ExtractRequired, ExtractSearchDirs
+    from .interpreter.interpreter import SourceOutputs
 
     from typing_extensions import TypedDict, Literal
 
@@ -163,6 +165,8 @@ _COMPILES_KWS: T.List[KwargInfo] = [_NAME_KW, _ARGS_KW, _DEPENDENCIES_KW, _INCLU
 _HEADER_KWS: T.List[KwargInfo] = [REQUIRED_KW.evolve(since='0.50.0', default=False), *_COMMON_KWS]
 
 class CompilerHolder(ObjectHolder['Compiler']):
+    preprocess_uid = itertools.count()
+
     def __init__(self, compiler: 'Compiler', interpreter: 'Interpreter'):
         super().__init__(compiler, interpreter)
         self.environment = self.env
@@ -750,7 +754,7 @@ class CompilerHolder(ObjectHolder['Compiler']):
         return self.compiler.get_argument_syntax()
 
     @FeatureNew('compiler.preprocess', '0.64.0')
-    @typed_pos_args('compiler.preprocess', varargs=(mesonlib.File, str), min_varargs=1)
+    @typed_pos_args('compiler.preprocess', varargs=(str, mesonlib.File, build.CustomTarget, build.CustomTargetIndex, build.GeneratedList), min_varargs=1)
     @typed_kwargs(
         'compiler.preprocess',
         KwargInfo('output', str, default='@PLAINNAME@.i'),
@@ -759,20 +763,25 @@ class CompilerHolder(ObjectHolder['Compiler']):
     )
     def preprocess_method(self, args: T.Tuple[T.List['mesonlib.FileOrString']], kwargs: 'PreprocessKW') -> T.List[build.CustomTargetIndex]:
         compiler = self.compiler.get_preprocessor()
-        sources = self.interpreter.source_strings_to_files(args[0])
+        sources: 'SourceOutputs' = self.interpreter.source_strings_to_files(args[0])
+        if any(isinstance(s, (build.CustomTarget, build.CustomTargetIndex, build.GeneratedList)) for s in sources):
+            FeatureNew.single_use('compiler.preprocess with generated sources', '1.1.0', self.subproject,
+                                  location=self.current_node)
         tg_kwargs = {
             f'{self.compiler.language}_args': kwargs['compile_args'],
             'build_by_default': False,
             'include_directories': kwargs['include_directories'],
         }
+        tg_name = f'preprocessor_{next(self.preprocess_uid)}'
         tg = build.CompileTarget(
-            'preprocessor',
+            tg_name,
             self.interpreter.subdir,
             self.subproject,
             self.environment,
             sources,
             kwargs['output'],
             compiler,
+            self.interpreter.backend,
             tg_kwargs)
         self.interpreter.add_target(tg.name, tg)
         # Expose this target as list of its outputs, so user can pass them to

test cases/common/259 preprocess/bar.c

@@ -1,3 +1,3 @@
-int bar(void) {
+int @BAR@(void) {
     return BAR;
 }

test cases/common/259 preprocess/meson.build

@@ -4,7 +4,16 @@ cc = meson.get_compiler('c')
 
 add_project_arguments(['-DFOO=0', '-DBAR=0'], language: 'c')
 
-pp_files = cc.preprocess('foo.c', 'bar.c', output: '@PLAINNAME@')
+fs = import('fs')
+bar_content = fs.read('bar.c')
+bar_c = custom_target(
+  input: 'bar.c',
+  output: 'bar.c',
+  command: ['python3', '-c', '''import sys;print(sys.argv[1].replace('@BAR@', 'bar'))''', bar_content],
+  capture: true,
+)
+
+pp_files = cc.preprocess('foo.c', bar_c, output: '@PLAINNAME@')
 
 foreach f : pp_files
   message(f.full_path())