gdb: Introduce new language field la_is_string_type_p

This commit is preparation work for the next commit, and by itself
makes no user visible change to GDB.  I've split this work into a
separate commit in order to make code review easier.

This commit adds a new field 'la_is_string_type_p' to the language
struct, this predicate will return true if a type is a string type for
the given language.

Some languages already have a "is this a string" predicate that I was
able to reuse, while for other languages I've had to add a new
predicate.  In this case I took inspiration from the value printing
code for that language - what different conditions would result in
printing something as a string.

A default "is this a string" method has also been added that looks for
TYPE_CODE_STRING, this is the fallback I've used for a couple of
languages.

In this commit I add the new field and initialise it for each
language, however at this stage the new field is never used.

gdb/ChangeLog:

	* ada-lang.c (ada_language_defn): Initialise new field.
	* c-lang.c (c_is_string_type_p): New function.
	(c_language_defn): Initialise new field.
	(cplus_language_defn): Initialise new field.
	(asm_language_defn): Initialise new field.
	(minimal_language_defn): Initialise new field.
	* c-lang.h (c_is_string_type_p): Declare new function.
	* d-lang.c (d_language_defn): Initialise new field.
	* f-lang.c (f_is_string_type_p): New function.
	(f_language_defn): Initialise new field.
	* go-lang.c (go_is_string_type_p): New function.
	(go_language_defn): Initialise new field.
	* language.c (default_is_string_type_p): New function.
	(unknown_language_defn): Initialise new field.
	(auto_language_defn): Initialise new field.
	* language.h (struct language_defn) <la_is_string_type_p>: New
	member variable.
	(default_is_string_type_p): Declare new function.
	* m2-lang.c (m2_language_defn): Initialise new field.
	* objc-lang.c (objc_language_defn): Initialise new field.
	* opencl-lang.c (opencl_language_defn): Initialise new field.
	* p-lang.c (pascal_is_string_type_p): New function.
	(pascal_language_defn): Initialise new field.
	* rust-lang.c (rust_is_string_type_p): New function.
	(rust_language_defn): Initialise new field.

1 files changed, 22 insertions, 0 deletions

diff --git a/gdb/m2-lang.c b/gdb/m2-lang.c
index 9f2a97d54fd..6fe628978cf 100644
--- a/gdb/m2-lang.c
+++ b/gdb/m2-lang.c
@@ -174,6 +174,27 @@ m2_printstr (struct ui_file *stream, struct type *type, const gdb_byte *string,
     fputs_filtered ("...", stream);
 }
 
+/* Return true if TYPE is a string.  */
+
+static bool
+m2_is_string_type_p (struct type *type)
+{
+  type = check_typedef (type);
+  if (TYPE_CODE (type) == TYPE_CODE_ARRAY
+      && TYPE_LENGTH (type) > 0
+      && TYPE_LENGTH (TYPE_TARGET_TYPE (type)) > 0)
+    {
+      struct type *elttype = check_typedef (TYPE_TARGET_TYPE (type));
+
+      if (TYPE_LENGTH (elttype) == 1
+	  && (TYPE_CODE (elttype) == TYPE_CODE_INT
+	      || TYPE_CODE (elttype) == TYPE_CODE_CHAR))
+	return true;
+    }
+
+  return false;
+}
+
 static struct value *
 evaluate_subexp_modula2 (struct type *expect_type, struct expression *exp,
 			 int *pos, enum noside noside)
@@ -399,6 +420,7 @@ extern const struct language_defn m2_language_defn =
   &default_varobj_ops,
   NULL,
   NULL,
+  m2_is_string_type_p,
   "{...}"			/* la_struct_too_deep_ellipsis */
 };