Fix test_move reporting collision when touching another body

Reporting rest collision information is needed for move_and_collide and
move_and_slide so floor detection can be done properly, but in the case
of just testing the motion for collision, it makes sense to return false
if the body is able to move all along the path without being stopped.

Updated the logic in test_move and clarified the documentation for
test_move and move_and_collide.

4 files changed, 28 insertions, 8 deletions

diff --git a/doc/classes/PhysicsBody2D.xml b/doc/classes/PhysicsBody2D.xml
index e108ab6298..7775cfb2f9 100644
--- a/doc/classes/PhysicsBody2D.xml
+++ b/doc/classes/PhysicsBody2D.xml
@@ -30,7 +30,7 @@
 			<argument index="2" name="safe_margin" type="float" default="0.08" />
 			<description>
 				Moves the body along the vector [code]linear_velocity[/code]. This method should be used in [method Node._physics_process] (or in a method called by [method Node._physics_process]), as it uses the physics step's [code]delta[/code] value automatically in calculations. Otherwise, the simulation will run at an incorrect speed.
-				The body will stop if it collides. Returns a [KinematicCollision2D], which contains information about the collision.
+				The body will stop if it collides. Returns a [KinematicCollision2D], which contains information about the collision when stopped, or when touching another body along the motion.
 				If [code]test_only[/code] is [code]true[/code], the body does not move but the would-be collision information is given.
 				[code]safe_margin[/code] is the extra margin used for collision recovery (see [member CharacterBody2D.collision/safe_margin] for more details).
 			</description>
@@ -50,8 +50,8 @@
 			<argument index="3" name="safe_margin" type="float" default="0.08" />
 			<description>
 				Checks for collisions without moving the body. This method should be used in [method Node._physics_process] (or in a method called by [method Node._physics_process]), as it uses the physics step's [code]delta[/code] value automatically in calculations. Otherwise, the simulation will run at an incorrect speed.
-				Virtually sets the node's position, scale and rotation to that of the given [Transform2D], then tries to move the body along the vector [code]linear_velocity[/code]. Returns [code]true[/code] if a collision would occur.
-				[code]collision[/code] is an optional object of type [KinematicCollision2D], which contains additional information about the collision (should there be one).
+				Virtually sets the node's position, scale and rotation to that of the given [Transform2D], then tries to move the body along the vector [code]linear_velocity[/code]. Returns [code]true[/code] if a collision would stop the body from moving along the whole path.
+				[code]collision[/code] is an optional object of type [KinematicCollision2D], which contains additional information about the collision when stopped, or when touching another body along the motion.
 				[code]safe_margin[/code] is the extra margin used for collision recovery (see [member CharacterBody2D.collision/safe_margin] for more details).
 			</description>
 		</method>
diff --git a/doc/classes/PhysicsBody3D.xml b/doc/classes/PhysicsBody3D.xml
index 8718c0caa2..9cf587f2e0 100644
--- a/doc/classes/PhysicsBody3D.xml
+++ b/doc/classes/PhysicsBody3D.xml
@@ -38,7 +38,7 @@
 			<argument index="3" name="max_collisions" type="int" default="1" />
 			<description>
 				Moves the body along the vector [code]linear_velocity[/code]. This method should be used in [method Node._physics_process] (or in a method called by [method Node._physics_process]), as it uses the physics step's [code]delta[/code] value automatically in calculations. Otherwise, the simulation will run at an incorrect speed.
-				The body will stop if it collides. Returns a [KinematicCollision3D], which contains information about the collision.
+				The body will stop if it collides. Returns a [KinematicCollision3D], which contains information about the collision when stopped, or when touching another body along the motion.
 				If [code]test_only[/code] is [code]true[/code], the body does not move but the would-be collision information is given.
 				[code]safe_margin[/code] is the extra margin used for collision recovery (see [member CharacterBody3D.collision/safe_margin] for more details).
 				[code]max_collisions[/code] allows to retrieve more than one collision result.
@@ -68,8 +68,8 @@
 			<argument index="4" name="max_collisions" type="int" default="1" />
 			<description>
 				Checks for collisions without moving the body. This method should be used in [method Node._physics_process] (or in a method called by [method Node._physics_process]), as it uses the physics step's [code]delta[/code] value automatically in calculations. Otherwise, the simulation will run at an incorrect speed.
-				Virtually sets the node's position, scale and rotation to that of the given [Transform3D], then tries to move the body along the vector [code]linear_velocity[/code]. Returns [code]true[/code] if a collision would occur.
-				[code]collision[/code] is an optional object of type [KinematicCollision3D], which contains additional information about the collision (should there be one).
+				Virtually sets the node's position, scale and rotation to that of the given [Transform3D], then tries to move the body along the vector [code]linear_velocity[/code]. Returns [code]true[/code] if a collision would stop the body from moving along the whole path.
+				[code]collision[/code] is an optional object of type [KinematicCollision3D], which contains additional information about the collision when stopped, or when touching another body along the motion.
 				[code]safe_margin[/code] is the extra margin used for collision recovery (see [member CharacterBody3D.collision/safe_margin] for more details).
 				[code]max_collisions[/code] allows to retrieve more than one collision result.
 			</description>
diff --git a/scene/2d/physics_body_2d.cpp b/scene/2d/physics_body_2d.cpp
index a43d498a62..2c17515a9e 100644
--- a/scene/2d/physics_body_2d.cpp
+++ b/scene/2d/physics_body_2d.cpp
@@ -133,9 +133,12 @@ bool PhysicsBody2D::test_move(const Transform2D &p_from, const Vector2 &p_linear
 	ERR_FAIL_COND_V(!is_inside_tree(), false);
 
 	PhysicsServer2D::MotionResult *r = nullptr;
+	PhysicsServer2D::MotionResult temp_result;
 	if (r_collision.is_valid()) {
 		// Needs const_cast because method bindings don't support non-const Ref.
 		r = const_cast<PhysicsServer2D::MotionResult *>(&r_collision->result);
+	} else {
+		r = &temp_result;
 	}
 
 	// Hack in order to work with calling from _process as well as from _physics_process; calling from thread is risky.
@@ -143,7 +146,14 @@ bool PhysicsBody2D::test_move(const Transform2D &p_from, const Vector2 &p_linear
 
 	PhysicsServer2D::MotionParameters parameters(p_from, p_linear_velocity * delta, p_margin);
 
-	return PhysicsServer2D::get_singleton()->body_test_motion(get_rid(), parameters, r);
+	bool colliding = PhysicsServer2D::get_singleton()->body_test_motion(get_rid(), parameters, r);
+
+	if (colliding) {
+		// Don't report collision when the whole motion is done.
+		return (r->collision_safe_fraction < 1.0);
+	} else {
+		return false;
+	}
 }
 
 TypedArray<PhysicsBody2D> PhysicsBody2D::get_collision_exceptions() {
diff --git a/scene/3d/physics_body_3d.cpp b/scene/3d/physics_body_3d.cpp
index d0506227b4..058a854663 100644
--- a/scene/3d/physics_body_3d.cpp
+++ b/scene/3d/physics_body_3d.cpp
@@ -174,9 +174,12 @@ bool PhysicsBody3D::test_move(const Transform3D &p_from, const Vector3 &p_linear
 	ERR_FAIL_COND_V(!is_inside_tree(), false);
 
 	PhysicsServer3D::MotionResult *r = nullptr;
+	PhysicsServer3D::MotionResult temp_result;
 	if (r_collision.is_valid()) {
 		// Needs const_cast because method bindings don't support non-const Ref.
 		r = const_cast<PhysicsServer3D::MotionResult *>(&r_collision->result);
+	} else {
+		r = &temp_result;
 	}
 
 	// Hack in order to work with calling from _process as well as from _physics_process; calling from thread is risky
@@ -184,7 +187,14 @@ bool PhysicsBody3D::test_move(const Transform3D &p_from, const Vector3 &p_linear
 
 	PhysicsServer3D::MotionParameters parameters(p_from, p_linear_velocity * delta, p_margin);
 
-	return PhysicsServer3D::get_singleton()->body_test_motion(get_rid(), parameters, r);
+	bool colliding = PhysicsServer3D::get_singleton()->body_test_motion(get_rid(), parameters, r);
+
+	if (colliding) {
+		// Don't report collision when the whole motion is done.
+		return (r->collision_safe_fraction < 1.0);
+	} else {
+		return false;
+	}
 }
 
 void PhysicsBody3D::set_axis_lock(PhysicsServer3D::BodyAxis p_axis, bool p_lock) {