Remove null_block_symbol

This removes null_block_symbol.  It seemed simpler to me to change
initializations and returns to use value initialization rather than
null_block_symbol.  This also fixes up a few spots where
initialization was done piecemeal.

gdb/ChangeLog
2019-03-24  Tom Tromey  <tom@tromey.com>

	* ada-lang.c (standard_lookup): Simplify initialization.
	(ada_lookup_symbol_nonlocal): Simplify return.
	* solib-spu.c (spu_lookup_lib_symbol): Simplify return.
	* solib-darwin.c (darwin_lookup_lib_symbol): Simplify return.
	* solib-svr4.c (elf_lookup_lib_symbol): Simplify return.
	* rust-lang.c (rust_lookup_symbol_nonlocal): Simplify
	initialization.
	* solib.c (solib_global_lookup): Simplify.
	* symtab.c (null_block_symbol): Remove.
	(symbol_cache_lookup): Simplify returns.
	(lookup_language_this): Simplify returns.
	(lookup_symbol_aux): Simplify return.
	(lookup_local_symbol): Simplify returns.
	(lookup_global_symbol_from_objfile): Simplify return.
	(lookup_symbol_in_objfile_symtabs)
	(lookup_symbol_in_objfile_from_linkage_name): Simplify return.
	(lookup_symbol_via_quick_fns, lookup_symbol_in_static_block)
	(lookup_static_symbol, lookup_global_symbol): Simplify return.
	* cp-namespace.c (cp_lookup_bare_symbol)
	(cp_search_static_and_baseclasses, cp_lookup_symbol_via_imports)
	(cp_lookup_symbol_via_all_imports, cp_lookup_nested_symbol_1)
	(cp_lookup_nested_symbol): Don't use null_block_symbol.
	(cp_lookup_symbol_via_imports): Simplify initialization.
	(find_symbol_in_baseclass): Likewise.
	* symtab.h (null_block_symbol): Remove.
	* d-namespace.c (d_lookup_symbol): Don't use null_block_symbol.
	(d_lookup_nested_symbol, d_lookup_symbol_imports)
	(d_lookup_symbol_module): Likewise.
	(find_symbol_in_baseclass): Simplify initialization.

11 files changed, 71 insertions, 55 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index b831b28..2f63bc3 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,37 @@
 2019-03-24  Tom Tromey  <tom@tromey.com>
 
+	* ada-lang.c (standard_lookup): Simplify initialization.
+	(ada_lookup_symbol_nonlocal): Simplify return.
+	* solib-spu.c (spu_lookup_lib_symbol): Simplify return.
+	* solib-darwin.c (darwin_lookup_lib_symbol): Simplify return.
+	* solib-svr4.c (elf_lookup_lib_symbol): Simplify return.
+	* rust-lang.c (rust_lookup_symbol_nonlocal): Simplify
+	initialization.
+	* solib.c (solib_global_lookup): Simplify.
+	* symtab.c (null_block_symbol): Remove.
+	(symbol_cache_lookup): Simplify returns.
+	(lookup_language_this): Simplify returns.
+	(lookup_symbol_aux): Simplify return.
+	(lookup_local_symbol): Simplify returns.
+	(lookup_global_symbol_from_objfile): Simplify return.
+	(lookup_symbol_in_objfile_symtabs)
+	(lookup_symbol_in_objfile_from_linkage_name): Simplify return.
+	(lookup_symbol_via_quick_fns, lookup_symbol_in_static_block)
+	(lookup_static_symbol, lookup_global_symbol): Simplify return.
+	* cp-namespace.c (cp_lookup_bare_symbol)
+	(cp_search_static_and_baseclasses, cp_lookup_symbol_via_imports)
+	(cp_lookup_symbol_via_all_imports, cp_lookup_nested_symbol_1)
+	(cp_lookup_nested_symbol): Don't use null_block_symbol.
+	(cp_lookup_symbol_via_imports): Simplify initialization.
+	(find_symbol_in_baseclass): Likewise.
+	* symtab.h (null_block_symbol): Remove.
+	* d-namespace.c (d_lookup_symbol): Don't use null_block_symbol.
+	(d_lookup_nested_symbol, d_lookup_symbol_imports)
+	(d_lookup_symbol_module): Likewise.
+	(find_symbol_in_baseclass): Simplify initialization.
+
+2019-03-24  Tom Tromey  <tom@tromey.com>
+
 	* expression.h: Don't include symtab.h.
 	(struct block): Forward declare.
 
diff --git a/gdb/ada-lang.c b/gdb/ada-lang.c
index 6626164..692d52a 100644
--- a/gdb/ada-lang.c
+++ b/gdb/ada-lang.c
@@ -4758,7 +4758,7 @@ standard_lookup (const char *name, const struct block *block,
                  domain_enum domain)
 {
   /* Initialize it just to avoid a GCC false warning.  */
-  struct block_symbol sym = {NULL, NULL};
+  struct block_symbol sym = {};
 
   if (lookup_cached_symbol (name, domain, &sym.symbol, NULL))
     return sym.symbol;
@@ -5918,7 +5918,7 @@ ada_lookup_symbol_nonlocal (const struct language_defn *langdef,
 	return sym;
     }
 
-  return (struct block_symbol) {NULL, NULL};
+  return {};
 }
 
 
diff --git a/gdb/cp-namespace.c b/gdb/cp-namespace.c
index f8db3ed..5b352d1 100644
--- a/gdb/cp-namespace.c
+++ b/gdb/cp-namespace.c
@@ -217,7 +217,7 @@ cp_lookup_bare_symbol (const struct language_defn *langdef,
 	lang_this = lookup_language_this (langdef, block);
 
       if (lang_this.symbol == NULL)
-	return null_block_symbol;
+	return {};
 
 
       type = check_typedef (TYPE_TARGET_TYPE (SYMBOL_TYPE (lang_this.symbol)));
@@ -225,7 +225,7 @@ cp_lookup_bare_symbol (const struct language_defn *langdef,
 	 This can happen for lambda functions compiled with clang++,
 	 which outputs no name for the container class.  */
       if (TYPE_NAME (type) == NULL)
-	return null_block_symbol;
+	return {};
 
       /* Look for symbol NAME in this class.  */
       sym = cp_lookup_nested_symbol (type, name, block, domain);
@@ -252,7 +252,7 @@ cp_search_static_and_baseclasses (const char *name,
 {
   /* Check for malformed input.  */
   if (prefix_len + 2 > strlen (name) || name[prefix_len + 1] != ':')
-    return null_block_symbol;
+    return {};
 
   /* The class, namespace or function name is everything up to and
      including PREFIX_LEN.  */
@@ -272,7 +272,7 @@ cp_search_static_and_baseclasses (const char *name,
   if (scope_sym.symbol == NULL)
     scope_sym = lookup_global_symbol (scope.c_str (), block, VAR_DOMAIN);
   if (scope_sym.symbol == NULL)
-    return null_block_symbol;
+    return {};
 
   struct type *scope_type = SYMBOL_TYPE (scope_sym.symbol);
 
@@ -379,13 +379,10 @@ cp_lookup_symbol_via_imports (const char *scope,
 			      const int search_parents)
 {
   struct using_direct *current;
-  struct block_symbol sym;
+  struct block_symbol sym = {};
   int len;
   int directive_match;
 
-  sym.symbol = NULL;
-  sym.block = NULL;
-
   /* First, try to find the symbol in the given namespace if requested.  */
   if (search_scope_first)
     sym = cp_lookup_symbol_in_namespace (scope, name,
@@ -476,7 +473,7 @@ cp_lookup_symbol_via_imports (const char *scope,
 	}
     }
 
-  return null_block_symbol;
+  return {};
 }
 
 /* Helper function that searches an array of symbols for one named NAME.  */
@@ -621,7 +618,7 @@ cp_lookup_symbol_via_all_imports (const char *scope, const char *name,
       block = BLOCK_SUPERBLOCK (block);
     }
 
-  return null_block_symbol;
+  return {};
 }
 
 /* Searches for NAME in the current namespace, and by applying
@@ -808,10 +805,7 @@ find_symbol_in_baseclass (struct type *parent_type, const char *name,
 			  int is_in_anonymous)
 {
   int i;
-  struct block_symbol sym;
-
-  sym.symbol = NULL;
-  sym.block = NULL;
+  struct block_symbol sym = {};
 
   for (i = 0; i < TYPE_N_BASECLASSES (parent_type); ++i)
     {
@@ -902,7 +896,7 @@ cp_lookup_nested_symbol_1 (struct type *container_type,
 	return sym;
     }
 
-  return null_block_symbol;
+  return {};
 }
 
 /* Look up a symbol named NESTED_NAME that is nested inside the C++
@@ -979,7 +973,7 @@ cp_lookup_nested_symbol (struct type *parent_type,
 			      "cp_lookup_nested_symbol (...) = NULL"
 			      " (func/method)\n");
 	}
-      return null_block_symbol;
+      return {};
 
     default:
       internal_error (__FILE__, __LINE__,
diff --git a/gdb/d-namespace.c b/gdb/d-namespace.c
index ed23f58..4edef18 100644
--- a/gdb/d-namespace.c
+++ b/gdb/d-namespace.c
@@ -127,7 +127,7 @@ d_lookup_symbol (const struct language_defn *langdef,
 
 	  lang_this = lookup_language_this (language_def (language_d), block);
 	  if (lang_this.symbol == NULL)
-	    return null_block_symbol;
+	    return {};
 
 	  type = check_typedef (TYPE_TARGET_TYPE (SYMBOL_TYPE (lang_this.symbol)));
 	  classname = TYPE_NAME (type);
@@ -147,7 +147,7 @@ d_lookup_symbol (const struct language_defn *langdef,
 	 more that can be done.  */
       class_sym = lookup_global_symbol (classname.c_str (), block, domain);
       if (class_sym.symbol == NULL)
-	return null_block_symbol;
+	return {};
 
       /* Look for a symbol named NESTED in this class.  */
       sym = d_lookup_nested_symbol (SYMBOL_TYPE (class_sym.symbol),
@@ -246,12 +246,9 @@ static struct block_symbol
 find_symbol_in_baseclass (struct type *parent_type, const char *name,
 			  const struct block *block)
 {
-  struct block_symbol sym;
+  struct block_symbol sym = {};
   int i;
 
-  sym.symbol = NULL;
-  sym.block = NULL;
-
   for (i = 0; i < TYPE_N_BASECLASSES (parent_type); ++i)
     {
       struct type *base_type = TYPE_BASECLASS (parent_type, i);
@@ -349,7 +346,7 @@ d_lookup_nested_symbol (struct type *parent_type,
 
     case TYPE_CODE_FUNC:
     case TYPE_CODE_METHOD:
-      return null_block_symbol;
+      return {};
 
     default:
       gdb_assert_not_reached ("called with non-aggregate type.");
@@ -464,7 +461,7 @@ d_lookup_symbol_imports (const char *scope, const char *name,
 	}
     }
 
-  return null_block_symbol;
+  return {};
 }
 
 /* Searches for NAME in the current module, and by applying relevant
@@ -496,7 +493,7 @@ d_lookup_symbol_module (const char *scope, const char *name,
       block = BLOCK_SUPERBLOCK (block);
     }
 
-  return null_block_symbol;
+  return {};
 }
 
 /* The D-specific version of name lookup for static and global names
diff --git a/gdb/rust-lang.c b/gdb/rust-lang.c
index 1cd92ff..0c6c13d 100644
--- a/gdb/rust-lang.c
+++ b/gdb/rust-lang.c
@@ -2020,7 +2020,7 @@ rust_lookup_symbol_nonlocal (const struct language_defn *langdef,
 			     const struct block *block,
 			     const domain_enum domain)
 {
-  struct block_symbol result = {NULL, NULL};
+  struct block_symbol result = {};
 
   if (symbol_lookup_debug)
     {
diff --git a/gdb/solib-darwin.c b/gdb/solib-darwin.c
index b976b79..65a5b9a 100644
--- a/gdb/solib-darwin.c
+++ b/gdb/solib-darwin.c
@@ -653,7 +653,7 @@ darwin_lookup_lib_symbol (struct objfile *objfile,
 			  const char *name,
 			  const domain_enum domain)
 {
-  return (struct block_symbol) {NULL, NULL};
+  return {};
 }
 
 static gdb_bfd_ref_ptr
diff --git a/gdb/solib-spu.c b/gdb/solib-spu.c
index 4f5e8e0..0cce0c9 100644
--- a/gdb/solib-spu.c
+++ b/gdb/solib-spu.c
@@ -397,7 +397,7 @@ spu_lookup_lib_symbol (struct objfile *objfile,
 
   if (svr4_so_ops.lookup_lib_global_symbol != NULL)
     return svr4_so_ops.lookup_lib_global_symbol (objfile, name, domain);
-  return (struct block_symbol) {NULL, NULL};
+  return {};
 }
 
 /* Enable shared library breakpoint.  */
diff --git a/gdb/solib-svr4.c b/gdb/solib-svr4.c
index 14a471b..0b8cadb 100644
--- a/gdb/solib-svr4.c
+++ b/gdb/solib-svr4.c
@@ -3204,7 +3204,7 @@ elf_lookup_lib_symbol (struct objfile *objfile,
     }
 
   if (abfd == NULL || scan_dyntag (DT_SYMBOLIC, abfd, NULL, NULL) != 1)
-    return (struct block_symbol) {NULL, NULL};
+    return {};
 
   return lookup_global_symbol_from_objfile (objfile, name, domain);
 }
diff --git a/gdb/solib.c b/gdb/solib.c
index 017cd62..8cef5a0 100644
--- a/gdb/solib.c
+++ b/gdb/solib.c
@@ -1457,7 +1457,7 @@ solib_global_lookup (struct objfile *objfile,
 
   if (ops->lookup_lib_global_symbol != NULL)
     return ops->lookup_lib_global_symbol (objfile, name, domain);
-  return (struct block_symbol) {NULL, NULL};
+  return {};
 }
 
 /* Lookup the value for a specific symbol from dynamic symbol table.  Look
diff --git a/gdb/symtab.c b/gdb/symtab.c
index a99bd8e..d25f560 100644
--- a/gdb/symtab.c
+++ b/gdb/symtab.c
@@ -95,9 +95,6 @@ static struct block_symbol
   lookup_symbol_in_objfile (struct objfile *objfile, int block_index,
 			    const char *name, const domain_enum domain);
 
-/* See symtab.h.  */
-const struct block_symbol null_block_symbol = { NULL, NULL };
-
 /* Program space key for finding name and language of "main".  */
 
 static const struct program_space_data *main_progspace_key;
@@ -1339,7 +1336,7 @@ symbol_cache_lookup (struct symbol_cache *cache,
     {
       *bsc_ptr = NULL;
       *slot_ptr = NULL;
-      return (struct block_symbol) {NULL, NULL};
+      return {};
     }
 
   hash = hash_symbol_entry (objfile_context, name, domain);
@@ -1373,7 +1370,7 @@ symbol_cache_lookup (struct symbol_cache *cache,
 			  name, domain_name (domain));
     }
   ++bsc->misses;
-  return (struct block_symbol) {NULL, NULL};
+  return {};
 }
 
 /* Clear out SLOT.  */
@@ -1938,7 +1935,7 @@ lookup_language_this (const struct language_defn *lang,
 		      const struct block *block)
 {
   if (lang->la_name_of_this == NULL || block == NULL)
-    return (struct block_symbol) {NULL, NULL};
+    return {};
 
   if (symbol_lookup_debug > 1)
     {
@@ -1975,7 +1972,7 @@ lookup_language_this (const struct language_defn *lang,
 
   if (symbol_lookup_debug > 1)
     fprintf_unfiltered (gdb_stdlog, " = NULL\n");
-  return (struct block_symbol) {NULL, NULL};
+  return {};
 }
 
 /* Given TYPE, a structure/union,
@@ -2102,7 +2099,7 @@ lookup_symbol_aux (const char *name, symbol_name_match_type match_type,
 		  fprintf_unfiltered (gdb_stdlog,
 				      "lookup_symbol_aux (...) = NULL\n");
 		}
-	      return (struct block_symbol) {NULL, NULL};
+	      return {};
 	    }
 	}
     }
@@ -2152,7 +2149,7 @@ lookup_local_symbol (const char *name,
   /* Check if either no block is specified or it's a global block.  */
 
   if (static_block == NULL)
-    return (struct block_symbol) {NULL, NULL};
+    return {};
 
   while (block != static_block)
     {
@@ -2177,7 +2174,7 @@ lookup_local_symbol (const char *name,
 
   /* We've reached the end of the function without finding a result.  */
 
-  return (struct block_symbol) {NULL, NULL};
+  return {};
 }
 
 /* See symtab.h.  */
@@ -2262,7 +2259,7 @@ lookup_global_symbol_from_objfile (struct objfile *main_objfile,
 	return result;
     }
 
-  return (struct block_symbol) {NULL, NULL};
+  return {};
 }
 
 /* Check to see if the symbol is defined in one of the OBJFILE's
@@ -2312,7 +2309,7 @@ lookup_symbol_in_objfile_symtabs (struct objfile *objfile, int block_index,
 
   if (symbol_lookup_debug > 1)
     fprintf_unfiltered (gdb_stdlog, " = NULL\n");
-  return (struct block_symbol) {NULL, NULL};
+  return {};
 }
 
 /* Wrapper around lookup_symbol_in_objfile_symtabs for search_symbols.
@@ -2355,7 +2352,7 @@ lookup_symbol_in_objfile_from_linkage_name (struct objfile *objfile,
 	return result;
     }
 
-  return (struct block_symbol) {NULL, NULL};
+  return {};
 }
 
 /* A helper function that throws an exception when a symbol was found
@@ -2388,7 +2385,7 @@ lookup_symbol_via_quick_fns (struct objfile *objfile, int block_index,
   struct block_symbol result;
 
   if (!objfile->sf)
-    return (struct block_symbol) {NULL, NULL};
+    return {};
 
   if (symbol_lookup_debug > 1)
     {
@@ -2408,7 +2405,7 @@ lookup_symbol_via_quick_fns (struct objfile *objfile, int block_index,
 	  fprintf_unfiltered (gdb_stdlog,
 			      "lookup_symbol_via_quick_fns (...) = NULL\n");
 	}
-      return (struct block_symbol) {NULL, NULL};
+      return {};
     }
 
   bv = COMPUNIT_BLOCKVECTOR (cust);
@@ -2512,7 +2509,7 @@ lookup_symbol_in_static_block (const char *name,
   struct symbol *sym;
 
   if (static_block == NULL)
-    return (struct block_symbol) {NULL, NULL};
+    return {};
 
   if (symbol_lookup_debug)
     {
@@ -2605,7 +2602,7 @@ lookup_static_symbol (const char *name, const domain_enum domain)
   if (result.symbol != NULL)
     {
       if (SYMBOL_LOOKUP_FAILED_P (result))
-	return (struct block_symbol) {NULL, NULL};
+	return {};
       return result;
     }
 
@@ -2623,7 +2620,7 @@ lookup_static_symbol (const char *name, const domain_enum domain)
 
   /* Still pass NULL for OBJFILE_CONTEXT here.  */
   symbol_cache_mark_not_found (bsc, slot, NULL, name, domain);
-  return (struct block_symbol) {NULL, NULL};
+  return {};
 }
 
 /* Private data to be used with lookup_symbol_global_iterator_cb.  */
@@ -2687,7 +2684,7 @@ lookup_global_symbol (const char *name,
   if (result.symbol != NULL)
     {
       if (SYMBOL_LOOKUP_FAILED_P (result))
-	return (struct block_symbol) {NULL, NULL};
+	return {};
       return result;
     }
 
diff --git a/gdb/symtab.h b/gdb/symtab.h
index 85dc371..e4ee727 100644
--- a/gdb/symtab.h
+++ b/gdb/symtab.h
@@ -1159,10 +1159,6 @@ struct block_symbol
 
 extern const struct symbol_impl *symbol_impls;
 
-/* For convenience.  All fields are NULL.  This means "there is no
-   symbol".  */
-extern const struct block_symbol null_block_symbol;
-
 /* Note: There is no accessor macro for symbol.owner because it is
    "private".  */