Factor out shared backtrace code (#1793)

include/backtrace.hpp

@@ -0,0 +1,69 @@
+// SPDX-License-Identifier: MIT
+
+#ifndef RGBDS_BACKTRACE_HPP
+#define RGBDS_BACKTRACE_HPP
+
+#include <inttypes.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <vector>
+
+#include "style.hpp"
+
+static constexpr uint64_t TRACE_COLLAPSE = UINT64_MAX;
+
+extern uint64_t traceDepth;
+
+bool trace_ParseTraceDepth(char const *arg);
+
+template<typename T, typename M, typename N>
+void trace_PrintBacktrace(std::vector<T> const &stack, M getName, N getLineNo) {
+	auto printLocation = [&](T const &item) {
+		style_Set(stderr, STYLE_CYAN, true);
+		fputs(getName(item), stderr);
+		style_Set(stderr, STYLE_CYAN, false);
+		fprintf(stderr, "(%" PRIu32 ")", getLineNo(item));
+	};
+
+	size_t n = stack.size();
+
+	if (traceDepth == TRACE_COLLAPSE) {
+		fputs("   ", stderr); // Just three spaces; the fourth will be handled by the loop
+		for (size_t i = 0; i < n; ++i) {
+			style_Reset(stderr);
+			fprintf(stderr, " %s ", i == 0 ? "at" : "<-");
+			printLocation(stack[n - i - 1]);
+		}
+		putc('\n', stderr);
+	} else if (traceDepth == 0 || static_cast<size_t>(traceDepth) >= n) {
+		for (size_t i = 0; i < n; ++i) {
+			style_Reset(stderr);
+			fprintf(stderr, "    %s ", i == 0 ? "at" : "<-");
+			printLocation(stack[n - i - 1]);
+			putc('\n', stderr);
+		}
+	} else {
+		size_t last = traceDepth / 2;
+		size_t first = traceDepth - last;
+		size_t skipped = n - traceDepth;
+		for (size_t i = 0; i < first; ++i) {
+			style_Reset(stderr);
+			fprintf(stderr, "    %s ", i == 0 ? "at" : "<-");
+			printLocation(stack[n - i - 1]);
+			putc('\n', stderr);
+		}
+		style_Reset(stderr);
+		fprintf(stderr, "    ...%zu more%s\n", skipped, last ? "..." : "");
+		for (size_t i = n - last; i < n; ++i) {
+			style_Reset(stderr);
+			fputs("    <- ", stderr);
+			printLocation(stack[n - i - 1]);
+			putc('\n', stderr);
+		}
+	}
+
+	style_Reset(stderr);
+}
+
+#endif // RGBDS_BACKTRACE_HPP