Method has_changed

ci/fingerprint/core.py:146–206

Determine if a source file has changed since the last known modification time. Two-layer verification process: 1. Fast modification time check - if times match, return False immediately 2. Content verification - compute/use cached MD5 hash for accurate comparison

(self, src_path: Path, previous_modtime: float)

            raise IOError(f"Cannot read file {file_path}: {e}") from e

    def has_changed(self, src_path: Path, previous_modtime: float) -> bool:
        """
        Determine if a source file has changed since the last known modification time.

        Two-layer verification process:
        1. Fast modification time check - if times match, return False immediately
        2. Content verification - compute/use cached MD5 hash for accurate comparison

        Args:
            src_path: Path to the source file to check
            previous_modtime: Previously known modification time (Unix timestamp)

        Returns:
            True if the file has changed, False if unchanged

        Raises:
            FileNotFoundError: If source file doesn't exist
        """
        if not src_path.exists():
            raise FileNotFoundError(f"Source file not found: {src_path}")

        current_modtime = os.path.getmtime(src_path)

        # Optional mode: strictly use modification time only (no hashing)
        # This is required for toolchains that invalidate PCH on any newer
        # dependency regardless of content changes (e.g., Clang).
        if self._modtime_only:
            # Treat as changed only when file is newer than the reference time
            # (keeps behavior stable when reference is an external artifact's mtime)
            return current_modtime > previous_modtime

        # Layer 1: Quick modification time check
        if current_modtime == previous_modtime:
            return False  # No change detected

        file_key = str(src_path.resolve())  # Use absolute path as key

        # Layer 2: Content verification via hash comparison
        if file_key in self.cache:
            cached_entry = self.cache[file_key]
            previous_hash = (
                cached_entry.md5_hash
            )  # Store previous hash before potential update

            if current_modtime == cached_entry.modification_time:
                # File is cached with current modtime - use cached hash
                current_hash = cached_entry.md5_hash
            else:
                # Cache is stale - compute new hash
                current_hash = self._compute_md5(src_path)
                self._update_cache_entry(src_path, current_modtime, current_hash)

            # Compare current hash with previous cached hash
            # If they match, content hasn't actually changed despite modtime difference
            return current_hash != previous_hash

        else:
            # File not in cache - compute hash and cache it