feat: macro expantion

1 files changed, 100 insertions, 0 deletions

diff --git a/src/ui/macro_expander.h b/src/ui/macro_expander.h
new file mode 100644
index 0000000..cf87d86
--- /dev/null
+++ b/src/ui/macro_expander.h
@@ -0,0 +1,100 @@
+#pragma once
+
+#include <cstdint>
+#include <filesystem>
+#include <string>
+#include <string_view>
+#include <unordered_map>
+#include <vector>
+
+namespace Hsdbg
+{
+    // one preprocessing token. whitespace is dropped during tokenising, so a run
+    // of tokens is rendered back to text with a small spacing heuristic. the hide
+    // set is the classic preprocessor "blue paint": the names of macros that must
+    // not expand this token again, which is what keeps a self-referential macro
+    // from unrolling forever
+    enum class PpKind : uint8_t
+    {
+        Identifier,
+        Number,
+        String,
+        Char,
+        Punct,
+    };
+
+    struct PpToken
+    {
+        PpKind kind = PpKind::Identifier;
+        std::string text;
+        std::vector<std::string> hide;
+    };
+
+    // a single #define, object-like (BUFFER) or function-like (MAX(a, b)). the
+    // body is the replacement list as significant tokens, with #, ## and the
+    // parameter names left in place for substitution time
+    struct MacroDef
+    {
+        std::string name;
+        bool function_like = false;
+        bool variadic = false;
+        std::vector<std::string> params;
+        std::vector<PpToken> body;
+    };
+
+    // the set of #defines visible in a source file. built by scanning the file
+    // for #define / #undef directives in order, optionally following local
+    // "quote" includes one project deep. system <...> includes are ignored on
+    // purpose: this is meant for a project's own macros, not libc's
+    class MacroTable
+    {
+    public:
+        auto clear() -> void;
+
+        // scan already-loaded lines as the primary file, then chase local quote
+        // includes relative to base_dir off disk. either argument may be empty
+        auto build(const std::vector<std::string>& lines,
+                   const std::filesystem::path& base_dir) -> void;
+
+        auto find(std::string_view name) const -> const MacroDef*;
+
+        auto empty() const -> bool { return m_macros.empty(); }
+        auto size() const -> size_t { return m_macros.size(); }
+
+        // bumped every rebuild, so a consumer can tell its cached expansion is
+        // stale without comparing the whole table
+        auto revision() const -> uint64_t { return m_revision; }
+
+    private:
+        auto scan_lines(const std::vector<std::string>& lines,
+                        const std::filesystem::path& base_dir, int depth,
+                        std::vector<std::filesystem::path>& seen) -> void;
+        auto scan_path(const std::filesystem::path& path, int depth,
+                       std::vector<std::filesystem::path>& seen) -> void;
+
+        std::unordered_map<std::string, MacroDef> m_macros;
+        uint64_t m_revision = 0;
+    };
+
+    // the result of unrolling an expression one macro layer at a time. levels[0]
+    // is the input as written, levels[i] is the text after i rounds of expansion,
+    // and levels.back() is the fixpoint where nothing expands any further
+    struct MacroExpansion
+    {
+        std::vector<std::string> levels;
+
+        // names of macros that were actually expanded going into each level, so
+        // levels_expanded[i] describes what turned levels[i-1] into levels[i].
+        // index 0 is always empty
+        std::vector<std::vector<std::string>> expanded;
+
+        auto fully_expanded() const -> bool { return m_reached_fixpoint; }
+
+        bool m_reached_fixpoint = true;
+    };
+
+    // unroll input against the table, capping the number of layers so a
+    // pathological macro cannot hang the ui
+    auto expand_stages(const MacroTable& table, std::string_view input,
+                       int max_levels = 64) -> MacroExpansion;
+}