GDB/MI: Add new "--language LANG" command option.

Frontend sometimes need to evaluate expressions that are
language-specific. For instance, Eclipse uses the following
expression to determine the size of an address on the target:

    -data-evaluate-expression "sizeof (void*)"

Unfortunately, if the main of the program being debugged is not C,
this may not work. For instance, if the main is in Ada, you get...

    -data-evaluate-expression "sizeof (void*)"
    ^error,msg="No definition of \"sizeof\" in current context."

... and apparently decides to stop the debugging session as a result.
The  recommendation sent was to specifically set the language to C
before trying to evaluate the expression.  Something such as:

    1. save current language
    2. set language c
    3. -data-evaluate-expression "sizeof (void*)"
    4. Restore language

This has the same disadvantages as the ones outlined in the "Context
Management" section of the GDB/MI documentation regarding setting
the current thread or the current frame, thus recommending the use of
general command-line switches such as --frame, or --thread instead.

This patch follows the same steps for the language, adding a similar
new command option: --language LANG. Example of use:

    -data-evaluate-expression --language c "sizeof (void*)"
    ^done,value="4"

gdb/ChangeLog:

        * mi/mi-parse.h (struct mi_parse) <language>: New field.
        * mi/mi-main.c (mi_cmd_execute): Temporarily set language to
        PARSE->LANGUAGE during command execution, if set.
        * mi/mi-parse.c: Add "language.h" #include.
        (mi_parse): Add parsing of "--language" command option.

        * NEWS: Add entry mentioning the new "--language" command option.

gdb/testsuite/ChangeLog:

        * gdb.mi/mi-language.exp: New file.

gdb/doc/ChangeLog:

        * gdb.texinfo (Show): Add xref anchor for "show language" command.
        (Context management): Place current subsection text into its own
        subsubsection.  Add new subsubsection describing the "--language"
        command option.

2 files changed, 66 insertions, 0 deletions

diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 5d1de05..0b0f759 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2013-11-14  Joel Brobecker  <brobecker@adacore.com>
+
+	* gdb.mi/mi-language.exp: New file.
+
 2013-09-17  Keith Seitz  <keiths@redhat.com>
 
 	PR c++/7935
diff --git a/gdb/testsuite/gdb.mi/mi-language.exp b/gdb/testsuite/gdb.mi/mi-language.exp
new file mode 100644
index 0000000..550beec
--- /dev/null
+++ b/gdb/testsuite/gdb.mi/mi-language.exp
@@ -0,0 +1,62 @@
+# Copyright 2013 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/>.
+
+load_lib mi-support.exp
+set MIFLAGS "-i=mi"
+
+gdb_exit
+if [mi_gdb_start] {
+    continue
+}
+
+mi_gdb_test "set lang ada" \
+            ".*=cmd-param-changed,param=\"language\",value=\"ada\".*" \
+            "set lang ada"
+
+# Evaluate an expression that the Ada language is unable to parse.
+mi_gdb_test "-data-evaluate-expression \"sizeof (void*)\"" \
+            "\\^error,.*" \
+            "sizeof expression using current language"
+
+# Now, ask for the same expression to be parsed, but using the C
+# language.
+mi_gdb_test "-data-evaluate-expression --language c \"sizeof (void*)\"" \
+            "\\^done,value=\"$decimal\"" \
+            "sizeof expression using C language"
+
+# Double-check that the current language has not changed.
+mi_gdb_test "show lang ada" \
+            ".*The current source language is \\\\\"ada\\\\\".*" \
+            "set lang ada"
+
+# Test what happens when specifying an invalid language name...
+mi_gdb_test "-data-evaluate-expression --language invlang \"sizeof (void*)\"" \
+            "\\^error,msg=\"Invalid --language argument: invlang\"" \
+            "data-evaluate-expression with invalid language name"
+
+# Make sure that "--language auto" is also rejected.
+mi_gdb_test "-data-evaluate-expression --language auto \"sizeof (void*)\"" \
+            "\\^error,msg=\"Invalid --language argument: auto\"" \
+            "data-evaluate-expression with language auto"
+
+# Make sure that "--language local" is also rejected.
+mi_gdb_test "-data-evaluate-expression --language local \"sizeof (void*)\"" \
+            "\\^error,msg=\"Invalid --language argument: local\"" \
+            "data-evaluate-expression with language local"
+
+# Make sure that "--language unknown" is also rejected.
+mi_gdb_test "-data-evaluate-expression --language unknown \"sizeof (void*)\"" \
+            "\\^error,msg=\"Invalid --language argument: unknown\"" \
+            "data-evaluate-expression with language unknown"