From d2c4cd0f5657f26150759fb8ab19dd448646eb06 Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Thu, 5 Jan 2023 11:56:38 +0200
Subject: [PATCH] Report which targets participate in a dependency cycle

---
 source/lib/target.cpp | 21 +++++++++++++++++++--
 source/lib/target.h   |  9 +++++++++
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/source/lib/target.cpp b/source/lib/target.cpp
index d1aaf73..558b3b2 100644
--- a/source/lib/target.cpp
+++ b/source/lib/target.cpp
@@ -1,6 +1,7 @@
 #include <msp/core/algorithm.h>
 #include <msp/fs/stat.h>
 #include <msp/fs/utils.h>
+#include <msp/strings/utils.h>
 #include "builder.h"
 #include "filetarget.h"
 #include "sourcepackage.h"
@@ -11,6 +12,8 @@
 using namespace std;
 using namespace Msp;
 
+vector<Target *> Target::prepare_stack;
+
 Target::Target(Builder &b, const string &n):
 	builder(b),
 	name(n)
@@ -118,12 +121,26 @@ void Target::prepare()
 		return;
 	if(state==PREPARING)
 	{
-		builder.get_logger().log("problems", "Dependency cycle detected at %s", name);
-		problems.push_back("Dependency cycle detected");
+		auto i = find(prepare_stack, this);
+		if(i!=prepare_stack.end())
+		{
+			string cycle;
+			for(; i!=prepare_stack.end(); ++i)
+				append(cycle, " -> ", (*i)->name);
+			append(cycle, " -> ", name);
+			builder.get_logger().log("problems", "Dependency cycle detected: %s", cycle);
+			problems.push_back(format("Dependency cycle detected: %s", cycle));
+		}
+		else
+		{
+			builder.get_logger().log("problems", "Dependency cycle detected at %s", name);
+			problems.push_back("Dependency cycle detected");
+		}
 		state = BROKEN;
 		return;
 	}
 
+	PushPrepare _push(this);
 	state = PREPARING;
 	/* Prepare existing dependencies early, because their information may be
 	needed to find other dependencies. */
diff --git a/source/lib/target.h b/source/lib/target.h
index 0ba38f8..1ae268c 100644
--- a/source/lib/target.h
+++ b/source/lib/target.h
@@ -6,6 +6,7 @@
 #include <string>
 #include <vector>
 #include <sigc++/signal.h>
+#include <msp/core/noncopyable.h>
 #include <msp/time/timestamp.h>
 #include "libbuilder_api.h"
 
@@ -41,6 +42,12 @@ protected:
 		BROKEN
 	};
 
+	struct PushPrepare: Msp::NonCopyable
+	{
+		PushPrepare(Target *t) { prepare_stack.push_back(t); }
+		~PushPrepare() { prepare_stack.pop_back(); }
+	};
+
 public:
 	sigc::signal<void> signal_bubble_rebuild;
 	sigc::signal<void> signal_modified;
@@ -61,6 +68,8 @@ protected:
 	Dependencies side_effects;
 	Target *primary_target = 0;
 
+	static std::vector<Target *> prepare_stack;
+
 	Target(Builder &, const std::string &);
 public:
 	virtual ~Target() { }
-- 
2.43.0