Enable -Wshadow

This one really did bite me hard (see previous commit), so enable it by
default.

Fix some cases of shadowing throughout the codebase. None of these
change behavior, and all of these were correct code, and just tripped up
the warning.

configure

@@ -1153,14 +1153,14 @@ if test -z "$CFLAGS" ; then
     WARNFLAGS="-wd167 -wd556 -wd144"
   elif test "$cc_vendor" = "clang"; then
     CFLAGS="$_opt $_debug $_pipe"
-    WARNFLAGS="-Wall -Wno-switch -Wno-logical-op-parentheses -Wpointer-arith -Wundef -Wno-pointer-sign -Wmissing-prototypes"
+    WARNFLAGS="-Wall -Wno-switch -Wno-logical-op-parentheses -Wpointer-arith -Wundef -Wno-pointer-sign -Wmissing-prototypes -Wshadow"
     ERRORFLAGS="-Werror=implicit-function-declaration -Wno-error=deprecated-declarations -Wno-error=unused-function"
   elif test "$cc_vendor" != "gnu" ; then
     CFLAGS="$_opt $_debug $_pipe"
   else
     CFLAGS="$_opt $_debug $_pipe"
     WARNFLAGS="-Wall -Wno-switch -Wno-parentheses -Wpointer-arith -Wredundant-decls"
-    ERRORFLAGS="-Werror-implicit-function-declaration -Wno-error=deprecated-declarations -Wno-error=unused-function"
+    ERRORFLAGS="-Werror-implicit-function-declaration -Wno-error=deprecated-declarations -Wno-error=unused-function -Wshadow"
     extra_ldflags="$extra_ldflags"
   fi
 else

demux/demux_lavf.c

@@ -649,7 +649,7 @@ static int demux_open_lavf(demuxer_t *demuxer, enum demux_check check)
         t = av_dict_get(c->metadata, "title", NULL, 0);
         demuxer_add_chapter(demuxer, t ? bstr0(t->value) : bstr0(NULL),
                             start, end, i);
-        AVDictionaryEntry *t = NULL;
+        t = NULL;
         while ((t = av_dict_get(c->metadata, "", t, AV_DICT_IGNORE_SUFFIX))) {
             demuxer_add_chapter_info(demuxer, i, bstr0(t->key),
                                      bstr0(t->value));

mpvcore/input/input.c

@@ -1407,10 +1407,10 @@ static mp_cmd_t *get_cmd_from_keys(struct input_ctx *ictx, char *force_section,
 
 static void update_mouse_section(struct input_ctx *ictx)
 {
-    struct cmd_bind *cmd =
+    struct cmd_bind *bind =
         find_any_bind_for_key(ictx, NULL, 1, (int[]){MP_KEY_MOUSE_MOVE});
 
-    char *new_section = cmd ? cmd->owner->section : "default";
+    char *new_section = bind ? bind->owner->section : "default";
 
     char *old = ictx->mouse_section;
     ictx->mouse_section = new_section;

stream/rar.c

@@ -188,12 +188,12 @@ static int SkipFile(struct stream *s, int *count, rar_file_t ***file,
     const int name_offset = (hdr->flags & RAR_BLOCK_FILE_HAS_HIGH) ? (7+33) : (7+25);
     if (name_offset + name_size <= hdr->size) {
         const int max_size = name_offset + name_size;
-        bstr data = stream_peek(s, max_size);
-        if (data.len < max_size) {
+        bstr namedata = stream_peek(s, max_size);
+        if (namedata.len < max_size) {
             free(name);
             return -1;
         }
-        memcpy(name, &data.start[name_offset], name_size);
+        memcpy(name, &namedata.start[name_offset], name_size);
     }
 
     rar_file_t *current = NULL;

video/filter/vf_vavpp.c

@@ -342,8 +342,8 @@ static bool initialize(struct vf_priv_s *p)
             if (!num)
                 continue;
             VAProcDeinterlacingType algorithm = VAProcDeinterlacingBob;
-            for (int i=0; i<num; ++i) { // find Bob
-                if (caps[i].type != algorithm)
+            for (int n=0; n < num; n++) { // find Bob
+                if (caps[n].type != algorithm)
                     continue;
                 VAProcFilterParameterBufferDeinterlacing param;
                 param.type = VAProcFilterDeinterlacing;

video/filter/vf_yadif.c

@@ -311,16 +311,16 @@ static void filter_line_c(struct vf_priv_s *p, uint8_t *dst, uint8_t *prev, uint
         int spatial_score= FFABS(cur[-refs-1] - cur[+refs-1]) + FFABS(c-e)
                          + FFABS(cur[-refs+1] - cur[+refs+1]) - 1;
 
-#define CHECK(j)\
-    {   int score= FFABS(cur[-refs-1+j] - cur[+refs-1-j])\
+#define CHECK(x, j)\
+    {   int score##x= FFABS(cur[-refs-1+j] - cur[+refs-1-j])\
                  + FFABS(cur[-refs  +j] - cur[+refs  -j])\
                  + FFABS(cur[-refs+1+j] - cur[+refs+1-j]);\
-        if(score < spatial_score){\
-            spatial_score= score;\
+        if(score##x < spatial_score){\
+            spatial_score= score##x;\
             spatial_pred= (cur[-refs  +j] + cur[+refs  -j])>>1;\
 
-        CHECK(-1) CHECK(-2) }} }}
-        CHECK( 1) CHECK( 2) }} }}
+        CHECK(0, -1) CHECK(1, -2) }} }}
+        CHECK(0,  1) CHECK(1,  2) }} }}
 
         if(p->mode<2){
             int b= (prev2[-2*refs] + next2[-2*refs])>>1;

video/out/vo_vdpau.c

@@ -1356,7 +1356,6 @@ static void draw_image(struct vo *vo, mp_image_t *mpi)
             return;
         surface = (VdpVideoSurface)(intptr_t)reserved_mpi->planes[3];
         if (handle_preemption(vo) >= 0) {
-            VdpStatus vdp_st;
             const void *destdata[3] = {mpi->planes[0], mpi->planes[2],
                                        mpi->planes[1]};
             if (vc->image_format == IMGFMT_NV12)