Make check_platform.py skip the branches that only a Windows build compiles, so that it passes on the runtime and guards it again.

tools/check_platform.py scanned the raw text of each shared runtime file and knew nothing of preprocessor branches, so the Win32 use that input.c, mods_probe.c, rtss_limit.c, vk_cache_file.h, vk_dlaa.c, vk_dlssg.c, vk_dump.c, vk_ffx.cpp, vk_ffx4.cpp, vk_fg.cpp, vk_fg4.cpp and vk_pipeline.c keep behind #ifdef _WIN32 made it fail on every run, at f1a2a64e already: a check that always fails guards nothing. It now leaves out the lines of a Windows-only branch (#ifdef _WIN32, #if defined(_WIN32), #if _WIN32 up to their #else, #elif or #endif, the #else of #ifndef _WIN32 or #if !defined(_WIN32), and conditionals nested in them), found on the text with its comments blanked. Every other branch is still scanned, #elif defined(_WIN32) and #if defined(_WIN32) && X among them, which can fail the check but never lets a use through. docs/building.md lists the check and its test under "Checks".

Reproduced before the change: the check exited with 1 and these 12 FAIL lines on 2f640fb8; it now exits with 0. Checks that passed: the new tests/check_platform_test.py (guarded uses pass, unguarded ones fail, the repository's runtime passes; it fails before the change) and tools/check_content.py --staged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tools/check_platform.py

@@ -3,12 +3,15 @@
 
 Runtime code goes through runtime/platform/platform.h. The Win32 back ends of the window system are Win32 by design and
 are not scanned: files named *_win.c / *_win.cpp (runtime/ and runtime/ui/), whose SDL counterparts (*_sdl.*) serve
-other hosts. Any other file that still uses Win32 goes into ALLOWED with the reason; a file in ALLOWED that no longer
+other hosts. Nor are the branches of a shared file that only a Windows build compiles (windows_only_lines): a file
+with a portable path of its own may reach a Windows-only library there (the upscalers' DLLs, RivaTuner's shared
+memory). Any other file that still uses Win32 goes into ALLOWED with the reason; a file in ALLOWED that no longer
 matches is noted, so the entry gets removed.
 
 Usage: python tools/check_platform.py [--root DIR]   (DIR holds runtime/; default: the repository root)
 """
 import argparse
+import bisect
 import re
 import sys
 from pathlib import Path
@@ -54,11 +57,49 @@ def strip(text):
     return re.sub(r'"(?:\\.|[^"\\\n])*"', blank, text)
 
 
+DIRECTIVE = re.compile(r"#\s*(if|ifdef|ifndef|elif|else|endif)\b")
+WIN_IF = re.compile(r"#\s*(ifdef\s+_WIN32|if\s+defined\s*\(\s*_WIN32\s*\)|if\s+defined\s+_WIN32|if\s+_WIN32)$")
+WIN_IFNOT = re.compile(r"#\s*(ifndef\s+_WIN32|if\s+!\s*defined\s*\(\s*_WIN32\s*\)|if\s+!\s*defined\s+_WIN32)$")
+
+
+def windows_only_lines(code):
+    """The numbers (from 0) of the lines of code (comments blanked: strip) that only a Windows build compiles: the
+    branch of #ifdef _WIN32, #if defined(_WIN32) or #if _WIN32 up to its #else, #elif or #endif, the #else branch of
+    #ifndef _WIN32 or #if !defined(_WIN32), and whatever a conditional inside such a branch holds. The directives
+    themselves are not among them. Any other branch counts as compiled everywhere, #elif defined(_WIN32) and
+    #if defined(_WIN32) && X too: such a branch is scanned, which can fail the check but never lets a use through."""
+    lines, stack = set(), []   # stack: [kind ('win', 'notwin', 'other'), whether its open branch is Windows-only]
+    for n, line in enumerate(code.split("\n")):
+        s = line.strip()
+        m = DIRECTIVE.match(s)
+        if not m:
+            if any(w for _, w in stack):
+                lines.add(n)
+            continue
+        d = m.group(1)
+        if d in ("if", "ifdef", "ifndef"):
+            kind = "win" if WIN_IF.match(s) else "notwin" if WIN_IFNOT.match(s) else "other"
+            stack.append([kind, kind == "win"])
+        elif d == "else" and stack:
+            stack[-1][1] = stack[-1][0] == "notwin"
+        elif d == "elif" and stack:
+            stack[-1][1] = False
+        elif d == "endif" and stack:
+            stack.pop()
+    return lines
+
+
 def scan(path):
     raw = path.read_text(encoding="utf-8", errors="replace")
-    hits = [("include", m.group(0).strip()) for m in INCLUDE.finditer(raw)]
-    code = strip(raw)
-    hits += [("call", m.group(1)) for m in CALL_RE.finditer(code)]
+    code = strip(raw)   # the same lines as raw
+    skip = windows_only_lines(code)
+    starts = [0] + [i + 1 for i, c in enumerate(raw) if c == "\n"]
+
+    def guarded(pos):
+        return bisect.bisect_right(starts, pos) - 1 in skip
+    # an include's match can begin on the line before it (^\s* takes that line's newline): its end is on its own line
+    hits = [("include", m.group(0).strip()) for m in INCLUDE.finditer(raw) if not guarded(m.end() - 1)]
+    hits += [("call", m.group(1)) for m in CALL_RE.finditer(code) if not guarded(m.start())]
     return hits