[PATCH 1/1] gdb, fortran: Fix local variable lookup in Fortran parser.

[Abdul Basit Ijaz <abdul.b.ijaz@intel.com>]

This changes fixes https://sourceware.org/bugzilla/show_bug.cgi?id=34059.

The Fortran expression parser in GDB ("gdb/f-exp.y") previously performed
symbol lookup in this order when parsing identifiers:

- SEARCH_STRUCT_DOMAIN (types/structs)
- SEARCH_VFT (virtual function tables)
- SEARCH_MODULE_DOMAIN (modules)

It searched for "types before variables", causing type names from shared
libraries to shadow local variable names.

For a reproducer like the one given below, the Fortran parser fails to
look up local variable name "array" and treats it as a type value instead
of a variable, because there's a conflicting "array" type from system
libraries.

1 program test
2
3  ! Declare variables used in this test.
4  integer, dimension (-2:2) :: array
5
6  array = 1
7
8  print *, ""           ! Break here
9  print *, array
10
11 end program test

Before the change, GDB shows:

'''
./gdb --data-directory=./data-directory --args /tmp/a.out
GNU gdb (GDB) 18.0.50.20260408-git
Copyright (C) 2026 Free Software Foundation, Inc.
...
Reading symbols from /tmp/a.out...
(gdb) break 8
Breakpoint 1 at 0x11b3: file test.f90, line 8.
(gdb) run
Starting program: /tmp/a.out
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".

Breakpoint 1, test () at test.f90:8
8         print *, ""           ! Break here
(gdb) info locals
array = (1, 1, 1, 1, 1)
(gdb) print array
❌️ Attempt to use a type name as an expression
(gdb) ptype array
type = Type array
    Type, C_Union :: :: u
    PTR TO -> ( char :: scratch(0:15 ))
End Type array
'''

This issue is fixed in the Fortran expression parser in GDB ("gdb/f-exp.y")
by prioritizing SEARCH_VFT over other search domains during symbol lookup.
After the change, the 'array' variable is resolved to the correct value.

'''
(gdb) print array
$1 = (1, 1, 1, 1, 1)
(gdb) ptype array
type = integer(kind=4) (-2:2)
'''
---
 gdb/f-exp.y                               |  2 +-
 gdb/testsuite/gdb.fortran/vars-lookup.exp | 38 +++++++++++++++++++++++
 gdb/testsuite/gdb.fortran/vars-lookup.f90 | 29 +++++++++++++++++
 3 files changed, 68 insertions(+), 1 deletion(-)
 create mode 100644 gdb/testsuite/gdb.fortran/vars-lookup.exp
 create mode 100644 gdb/testsuite/gdb.fortran/vars-lookup.f90

diff --git a/gdb/f-exp.y b/gdb/f-exp.y
index 278e2091403..4216112c10b 100644
--- a/gdb/f-exp.y
+++ b/gdb/f-exp.y
@@ -1651,8 +1651,8 @@ yylex (void)
     struct block_symbol result;
     const domain_search_flags lookup_domains[] =
     {
-      SEARCH_STRUCT_DOMAIN,
       SEARCH_VFT,
+      SEARCH_STRUCT_DOMAIN,
       SEARCH_MODULE_DOMAIN
     };
     int hextype;
diff --git a/gdb/testsuite/gdb.fortran/vars-lookup.exp b/gdb/testsuite/gdb.fortran/vars-lookup.exp
new file mode 100644
index 00000000000..2c9be02f1dc
--- /dev/null
+++ b/gdb/testsuite/gdb.fortran/vars-lookup.exp
@@ -0,0 +1,38 @@
+# Copyright 2026 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Test the variable lookup.
+
+require allow_fortran_tests
+
+standard_testfile .f90
+load_lib fortran.exp
+
+if {[prepare_for_testing "failed to prepare" $testfile \
+	${srcfile} {debug f90}]} {
+    return
+}
+
+if {![fortran_runto_main]} {
+    return
+}
+
+set bp_loc [gdb_get_line_number "break-here"]
+gdb_breakpoint "$srcfile:$bp_loc"
+gdb_continue_to_breakpoint "stop-at-bp" ".*$srcfile:$bp_loc.*"
+
+set integer4 [fortran_int4]
+gdb_test "print array" "= \\(1, 1, 1, 1, 1\\)"
+gdb_test "ptype array" "type = $integer4 \\(-2:2\\)"
diff --git a/gdb/testsuite/gdb.fortran/vars-lookup.f90 b/gdb/testsuite/gdb.fortran/vars-lookup.f90
new file mode 100644
index 00000000000..9121cd007e6
--- /dev/null
+++ b/gdb/testsuite/gdb.fortran/vars-lookup.f90
@@ -0,0 +1,29 @@
+! Copyright 2026 Free Software Foundation, Inc.
+!
+! This program is free software; you can redistribute it and/or modify
+! it under the terms of the GNU General Public License as published by
+! the Free Software Foundation; either version 3 of the License, or
+! (at your option) any later version.
+!
+! This program is distributed in the hope that it will be useful,
+! but WITHOUT ANY WARRANTY; without even the implied warranty of
+! MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+! GNU General Public License for more details.
+!
+! You should have received a copy of the GNU General Public License
+! along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+! Source code for vars-lookup.exp.
+
+program test
+
+  implicit none
+  ! Declare variables used in this test.
+  integer, dimension (-2:2) :: array
+
+  array = 1
+
+  print *, "" ! break-here
+  print *, array
+
+end program test
-- 
2.34.1

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