[PATCH] Force array coercion in c_get_string

[Tom Tromey <tromey at adacore dot com>]

A user here noticed that the Python Value.string method did not work
for Ada arrays.  I tracked this down to an oddity in value_as_address
-- namely, it calls coerce_array, but that function will not force
array coercion when the language has c_style_arrays=false, as Ada
does.

This patch fixes the problem by forcing array coercion in
c_get_string.  Changing either value_as_address or coerce_array seemed
iffy to me.

Initially here I tried making arrays take the "in GDB's memory" branch
of the if near the top of c_get_string; but this fails the C struct
hack test case added for PR 16196.

Tested on x86-64 Fedora 29.

gdb/ChangeLog
2019-04-25  Tom Tromey  <tromey@adacore.com>

	* c-lang.c (c_get_string): Call value_coerce_array.

gdb/testsuite/ChangeLog
2019-04-25  Tom Tromey  <tromey@adacore.com>

	* gdb.python/py-value.exp (test_value_in_inferior): Add Ada test.
---
 gdb/ChangeLog                         | 4 ++++
 gdb/c-lang.c                          | 7 +++++++
 gdb/testsuite/ChangeLog               | 4 ++++
 gdb/testsuite/gdb.python/py-value.exp | 7 +++++++
 4 files changed, 22 insertions(+)

diff --git a/gdb/c-lang.c b/gdb/c-lang.c
index 33506f1d1ed..2084134c36d 100644
--- a/gdb/c-lang.c
+++ b/gdb/c-lang.c
@@ -306,6 +306,13 @@ c_get_string (struct value *value, gdb::unique_xmalloc_ptr<gdb_byte> *buffer,
     }
   else
     {
+      /* value_as_address calls coerce_array, but that won't actually
+	 coerce the array if c_style_arrays is false.  However, in
+	 this particular case, we do want to always force array
+	 coercion.  So, check this case here.  */
+      if (TYPE_CODE (type) == TYPE_CODE_ARRAY)
+	value = value_coerce_array (value);
+
       CORE_ADDR addr = value_as_address (value);
 
       /* Prior to the fix for PR 16196 read_string would ignore fetchlimit
diff --git a/gdb/testsuite/gdb.python/py-value.exp b/gdb/testsuite/gdb.python/py-value.exp
index b3d90b52272..7f42d31572a 100644
--- a/gdb/testsuite/gdb.python/py-value.exp
+++ b/gdb/testsuite/gdb.python/py-value.exp
@@ -315,6 +315,13 @@ proc test_value_in_inferior {} {
   gdb_test "python print (\"---\"+st.string (length = 0)+\"---\")" "------" "test string (length = 0) is empty"
   gdb_test "python print (len(st.string (length = 0)))" "0" "test length is 0"
 
+  # We choose Ada here to test a language where c_style_arrays is
+  # false.
+  gdb_test "set lang ada" \
+      "Warning: the current language does not match this frame."
+  gdb_test "python print (st.string ())"  "divide et impera"  \
+      "Test string with no length in ada"
+  gdb_test_no_output "set lang auto"
 
   # Fetch a string that has embedded nulls.
   gdb_test "print nullst" "\"divide\\\\000et\\\\000impera\".*"
-- 
2.20.1