Don't recursively look for a symbol in all imports of imported modules.

Given two or more modules that import each other's scope, the current symbol
lookup routines would go round in circles looking through each import from
each module, possibly checking the same module twice or more until all possible
paths are marked as "searched".

Given enough modules, this causes an exponential slowdown in time taken to find
symbols that do exist, and infinite recursion when they don't.

gdb/ChangeLog:
	* d-namespace.c (d_lookup_symbol_imports): Avoid recursive lookups from
	cyclic imports.

gdb/testsuite/ChangeLog:
	* gdb.dlang/circular.c: New file.
	* gdb.dlang/circular.exp: New file.

2 files changed, 182 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.dlang/circular.c b/gdb/testsuite/gdb.dlang/circular.c
new file mode 100644
index 0000000..a946e3f
--- /dev/null
+++ b/gdb/testsuite/gdb.dlang/circular.c
@@ -0,0 +1,33 @@
+/* Copyright 2016 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/>.  */
+
+asm ("circular1_found_start: .globl circular1_found_start");
+
+/* DWARF will describe this function as being inside a D module.  */
+
+void
+found (void)
+{
+}
+
+asm ("circular1_found_end: .globl circular1_found_end");
+
+int
+main (void)
+{
+  found ();
+  return 0;
+}
+
diff --git a/gdb/testsuite/gdb.dlang/circular.exp b/gdb/testsuite/gdb.dlang/circular.exp
new file mode 100644
index 0000000..c6eb789
--- /dev/null
+++ b/gdb/testsuite/gdb.dlang/circular.exp
@@ -0,0 +1,149 @@
+# Copyright (C) 2016 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 symbol lookup when there are multiple circular imports.
+
+load_lib "d-support.exp"
+load_lib "dwarf.exp"
+
+if { [skip_d_tests] } { continue }
+
+# This test can only be run on targets which support DWARF-2 and use gas.
+if {![dwarf2_support]} {
+    return 0
+}
+
+standard_testfile circular.c circular-dw.S
+
+# Make some DWARF for the test.
+set asm_file [standard_output_file $srcfile2]
+Dwarf::assemble $asm_file {
+    cu {} {
+	compile_unit {
+	    {language @DW_LANG_D}
+	} {
+	    declare_labels circular1_label circular2_label circular3_label
+	    declare_labels circular4_label circular5_label
+
+	    extern circular1_found_start circular1_found_end
+
+	    circular1_label: module {
+		{name circular1}
+	    } {
+		imported_module {
+		    {import :$circular2_label}
+		}
+		imported_module {
+		    {import :$circular3_label}
+		}
+		imported_module {
+		    {import :$circular4_label}
+		}
+		imported_module {
+		    {import :$circular5_label}
+		}
+
+		subprogram {
+		    {name found}
+		    {external 1 flag_present}
+		    {low_pc circular1_found_start addr}
+		    {high_pc circular1_found_end addr}
+		}
+	    }
+
+	    circular2_label: module {
+		{name circular2}
+	    } {
+		imported_module {
+		    {import :$circular1_label}
+		}
+		imported_module {
+		    {import :$circular3_label}
+		}
+		imported_module {
+		    {import :$circular4_label}
+		}
+		imported_module {
+		    {import :$circular5_label}
+		}
+	    }
+
+	    circular3_label: module {
+		{name circular3}
+	    } {
+		imported_module {
+		    {import :$circular1_label}
+		}
+		imported_module {
+		    {import :$circular2_label}
+		}
+		imported_module {
+		    {import :$circular4_label}
+		}
+		imported_module {
+		    {import :$circular5_label}
+		}
+	    }
+
+	    circular4_label: module {
+		{name circular4}
+	    } {
+		imported_module {
+		    {import :$circular1_label}
+		}
+		imported_module {
+		    {import :$circular2_label}
+		}
+		imported_module {
+		    {import :$circular3_label}
+		}
+		imported_module {
+		    {import :$circular5_label}
+		}
+	    }
+
+	    circular5_label: module {
+		{name circular5}
+	    } {
+		imported_module {
+		    {import :$circular1_label}
+		}
+		imported_module {
+		    {import :$circular2_label}
+		}
+		imported_module {
+		    {import :$circular3_label}
+		}
+		imported_module {
+		    {import :$circular4_label}
+		}
+	    }
+	}
+    }
+}
+
+if { [prepare_for_testing ${testfile}.exp ${testfile} \
+          [list $srcfile $asm_file] {nodebug}] } {
+    return -1
+}
+
+gdb_test_no_output "set language d"
+
+if {![runto "circular1.found"]} {
+    return -1
+}
+
+# This last test shouldn't timeout.
+gdb_test "print notfound" "No symbol \"notfound\" in current context."