From b8d50b112a66ef14e1b493baccd61e27f85104cf Mon Sep 17 00:00:00 2001
From: Thomas Watson <twatson52@icloud.com>
Date: Sat, 28 Oct 2023 12:58:32 -0500
Subject: [PATCH] AP_Compass: fix C++ One Definition Rule violations

Two structs with the same name must have exactly the same definition, no
matter where they occur in the program, otherwise the program is undefined.

Move each sample register struct definition into the associated class
definition so they are in a different namespace and no longer
identically named, thus fixing this issue.
---
 libraries/AP_Compass/AP_Compass_AK09916.cpp | 9 +--------
 libraries/AP_Compass/AP_Compass_AK09916.h   | 8 ++++++++
 libraries/AP_Compass/AP_Compass_AK8963.cpp  | 7 +------
 libraries/AP_Compass/AP_Compass_AK8963.h    | 6 ++++++
 libraries/AP_Compass/AP_Compass_LSM9DS1.cpp | 5 -----
 libraries/AP_Compass/AP_Compass_LSM9DS1.h   | 5 +++++
 6 files changed, 21 insertions(+), 19 deletions(-)

diff --git a/libraries/AP_Compass/AP_Compass_AK09916.cpp b/libraries/AP_Compass/AP_Compass_AK09916.cpp
index bb6732365a25d..8630da5e9747b 100644
--- a/libraries/AP_Compass/AP_Compass_AK09916.cpp
+++ b/libraries/AP_Compass/AP_Compass_AK09916.cpp
@@ -58,13 +58,6 @@ extern const AP_HAL::HAL &hal;
 
 extern const AP_HAL::HAL &hal;
 
-struct PACKED sample_regs {
-    uint8_t st1;
-    int16_t val[3];
-    uint8_t tmps;
-    uint8_t st2;
-};
-
 AP_Compass_AK09916::AP_Compass_AK09916(AP_AK09916_BusDriver *bus,
                                         bool force_external,
                                         enum Rotation rotation)
@@ -477,7 +470,7 @@ bool AP_AK09916_BusDriver_Auxiliary::configure()
 
 bool AP_AK09916_BusDriver_Auxiliary::start_measurements()
 {
-    if (_bus->register_periodic_read(_slave, REG_ST1, sizeof(sample_regs)) < 0) {
+    if (_bus->register_periodic_read(_slave, REG_ST1, sizeof(AP_Compass_AK09916::sample_regs)) < 0) {
         return false;
     }
 
diff --git a/libraries/AP_Compass/AP_Compass_AK09916.h b/libraries/AP_Compass/AP_Compass_AK09916.h
index b4cca6e97346e..5c80cff9ef675 100644
--- a/libraries/AP_Compass/AP_Compass_AK09916.h
+++ b/libraries/AP_Compass/AP_Compass_AK09916.h
@@ -75,6 +75,14 @@ class AP_Compass_AK09916 : public AP_Compass_Backend
 
     void read() override;
 
+    /* Must be public so the BusDriver can access its definition */
+    struct PACKED sample_regs {
+        uint8_t st1;
+        int16_t val[3];
+        uint8_t tmps;
+        uint8_t st2;
+    };
+
 private:
     AP_Compass_AK09916(AP_AK09916_BusDriver *bus, bool force_external,
                        enum Rotation rotation);
diff --git a/libraries/AP_Compass/AP_Compass_AK8963.cpp b/libraries/AP_Compass/AP_Compass_AK8963.cpp
index 4c4ced9e3f5c8..ad6a8c6d234ef 100644
--- a/libraries/AP_Compass/AP_Compass_AK8963.cpp
+++ b/libraries/AP_Compass/AP_Compass_AK8963.cpp
@@ -49,11 +49,6 @@
 
 #define AK8963_MILLIGAUSS_SCALE 10.0f
 
-struct PACKED sample_regs {
-    int16_t val[3];
-    uint8_t st2;
-};
-
 extern const AP_HAL::HAL &hal;
 
 AP_Compass_AK8963::AP_Compass_AK8963(AP_AK8963_BusDriver *bus,
@@ -379,7 +374,7 @@ bool AP_AK8963_BusDriver_Auxiliary::configure()
 
 bool AP_AK8963_BusDriver_Auxiliary::start_measurements()
 {
-    if (_bus->register_periodic_read(_slave, AK8963_HXL, sizeof(sample_regs)) < 0) {
+    if (_bus->register_periodic_read(_slave, AK8963_HXL, sizeof(AP_Compass_AK8963::sample_regs)) < 0) {
         return false;
     }
 
diff --git a/libraries/AP_Compass/AP_Compass_AK8963.h b/libraries/AP_Compass/AP_Compass_AK8963.h
index 7b61768d84225..c0f020756571a 100644
--- a/libraries/AP_Compass/AP_Compass_AK8963.h
+++ b/libraries/AP_Compass/AP_Compass_AK8963.h
@@ -39,6 +39,12 @@ class AP_Compass_AK8963 : public AP_Compass_Backend
 
     void read() override;
 
+    /* Must be public so the BusDriver can access its definition */
+    struct PACKED sample_regs {
+        int16_t val[3];
+        uint8_t st2;
+    };
+
 private:
     AP_Compass_AK8963(AP_AK8963_BusDriver *bus,
                       enum Rotation rotation);
diff --git a/libraries/AP_Compass/AP_Compass_LSM9DS1.cpp b/libraries/AP_Compass/AP_Compass_LSM9DS1.cpp
index eeebe00fdca5c..60db0f54de622 100644
--- a/libraries/AP_Compass/AP_Compass_LSM9DS1.cpp
+++ b/libraries/AP_Compass/AP_Compass_LSM9DS1.cpp
@@ -47,11 +47,6 @@
 #define LSM9DS1M_INT_THS_L_M        0x32
 #define LSM9DS1M_INT_THS_H_M        0x33
 
-struct PACKED sample_regs {
-    uint8_t status;
-    int16_t val[3];
-};
-
 extern const AP_HAL::HAL &hal;
 
 AP_Compass_LSM9DS1::AP_Compass_LSM9DS1(AP_HAL::OwnPtr<AP_HAL::Device> dev,
diff --git a/libraries/AP_Compass/AP_Compass_LSM9DS1.h b/libraries/AP_Compass/AP_Compass_LSM9DS1.h
index 2cb91c74c6de4..7017883bd62ad 100644
--- a/libraries/AP_Compass/AP_Compass_LSM9DS1.h
+++ b/libraries/AP_Compass/AP_Compass_LSM9DS1.h
@@ -42,6 +42,11 @@ class AP_Compass_LSM9DS1 : public AP_Compass_Backend
     uint8_t _compass_instance;
     float _scaling;
     enum Rotation _rotation;
+
+    struct PACKED sample_regs {
+        uint8_t status;
+        int16_t val[3];
+    };
 };
 
 #endif