compat: Generate a proper depfile with all inputs

Turns out compile_commands.json only lists a subset of the inputs, so we
would end up generating an incomplete depfile, causing unreliable
incremental builds.

So to solve this, we instead query Ninja for the inputs of each target.
This also gives us better granularity, as previously all of the outputs
would have the same inputs, and would all get invalidated if only one of
them changed.

compat/build.py

@@ -4,7 +4,6 @@
 from collections import OrderedDict
 from dataclasses import dataclass, field
 import itertools
-import json
 import os
 from pathlib import Path
 import pickle
@@ -19,6 +18,7 @@
 
 
 REPO_ROOT = Path(__file__).resolve().parent.parent
+NINJA = os.environ.get("NINJA", "ninja")
 
 
 Role = Literal["project", "subproject"]
@@ -373,10 +373,11 @@ def call_internal_meson(argv, *args, **kwargs):
             silenced_kwargs = kwargs
         return call_meson(argv, *args, **silenced_kwargs)
 
-    source_paths: set[Path] = set()
     options: Optional[Sequence[str]] = None
     build_env = scrub_environment(os.environ)
     build_env["FRIDA_RELENG"] = str(releng_location)
+    top_builddir = state.top_builddir
+    depfile_lines = []
     for group, outputs in state.outputs.items():
         if group.arch is None:
             for o in outputs:
@@ -387,7 +388,7 @@ def call_internal_meson(argv, *args, **kwargs):
 
         if not (workdir / "build.ninja").exists():
             if options is None:
-                options = load_meson_options(state.top_builddir, state.role, set(subprojects.keys()))
+                options = load_meson_options(top_builddir, state.role, set(subprojects.keys()))
                 version_opt = next((opt for opt in options if opt.startswith("-Dfrida_version=")), None)
                 if version_opt is None:
                     options += [f"-Dfrida_version={state.frida_version}"]
@@ -420,14 +421,18 @@ def call_internal_meson(argv, *args, **kwargs):
         for o in outputs:
             shutil.copy(workdir / o.file, state.builddir / o.name)
 
-        for cmd in json.loads((workdir / "compile_commands.json").read_text(encoding="utf-8")):
-            source_paths.add((workdir / Path(cmd["file"])).absolute())
+            output_relpath = (workdir / o.name).relative_to(top_builddir).as_posix()
+            raw_inputs = subprocess.run([NINJA, "-t", "inputs", o.file],
+                                        cwd=workdir,
+                                        capture_output=True,
+                                        encoding="utf-8",
+                                        check=True).stdout.rstrip().split("\n")
+            input_paths = [workdir / relpath for relpath in raw_inputs]
+            input_relpaths = [Path(os.path.relpath(p, top_builddir)).as_posix() for p in input_paths]
+            quoted_input_relpaths = " ".join([quote(p) for p in input_relpaths])
+            depfile_lines.append(f"{output_relpath}: {quoted_input_relpaths}")
 
-    (state.builddir / DEPFILE_FILENAME).write_text(generate_depfile(itertools.chain.from_iterable(state.outputs.values()),
-                                                                    source_paths,
-                                                                    state.builddir,
-                                                                    state.top_builddir),
-                                                   encoding="utf-8")
+    (state.builddir / DEPFILE_FILENAME).write_text("\n".join(depfile_lines), encoding="utf-8")
 
 
 def load_meson_options(top_builddir: Path,
@@ -511,18 +516,6 @@ def scrub_windows_devenv_dirs_from_path(raw_path: str, env: Mapping[str, str]) -
     return ";".join(clean_entries)
 
 
-def generate_depfile(outputs: Sequence[Output],
-                     source_paths: Sequence[Path],
-                     builddir: Path,
-                     top_builddir: Path) -> str:
-    output_relpaths = [(builddir / o.name).relative_to(top_builddir).as_posix() for o in outputs]
-    inputs = " ".join([quote(Path(os.path.relpath(p, top_builddir)).as_posix()) for p in source_paths if p.exists()])
-    lines = []
-    for output in output_relpaths:
-        lines.append(f"{output}: {inputs}")
-    return "\n".join(lines)
-
-
 def quote(path: str) -> str:
     if " " not in path:
         return path