[2/2] gdb: Introduce 'print max-depth' feature

  Introduce a new print setting max-depth which can be set with 'set
print max-depth DEPTH'.  The default value of DEPTH is 20, but this
can also be set to unlimited.

When GDB is printing a value containing nested structures GDB will
stop descending at depth DEPTH.  Here is a small example:

    typedef struct s1 { int a; } s1;
    typedef struct s2 { s1 b; } s2;
    typedef struct s3 { s2 c; } s3;
    typedef struct s4 { s3 d; } s4;

    s4 var = { { { { 3 } } } };

The following table shows how various depth settings effect printing
of 'var':

    | Depth Setting | Result of 'p var'              |
    |---------------+--------------------------------|
    |     Unlimited | $1 = {d = {c = {b = {a = 3}}}} |
    |             4 | $1 = {d = {c = {b = {a = 3}}}} |
    |             3 | $1 = {d = {c = {b = {...}}}}   |
    |             2 | $1 = {d = {c = {...}}}         |
    |             1 | $1 = {d = {...}}               |
    |             0 | $1 = {...}                     |

Only structures, unions, and arrays are replaced in this way, scalars
and strings are not replaced.

The replacement is counted from the level at which you print, not from
the top level of the structure.  So, consider the above example and
this GDB session:

    (gdb) set print max-depth 2
    (gdb) p var
    $1 = {d = {c = {...}}}
    (gdb) p var.d
    $2 = {c = {b = {...}}}
    (gdb) p var.d.c
    $3 = {b = {a = 3}}

Setting the max-depth to 2 doesn't prevent the user from exploring
deeper into 'var' by asking for specific sub-fields to be printed.

The motivation behind this feature is to try and give the user more
control over how much is printed when examining large, complex data
structures.

The default max-depth of 20 means that there is a change in GDB's
default behaviour.  Someone printing a data structure with 20 levels
of nesting will now see '{...}' instead of their data, they would need
to adjust the max depth, or call print again naming a specific field
in order to dig deeper into their data structure.  If this is
considered a problem then we could increase the default, or even make
the default unlimited.

This commit relies on the previous commit, which added a new field to
the language structure, this new field was a string that contained the
pattern that should be used when a structure/union/array is replaced
in the output, this allows languages to use a syntax that is more
appropriate, mostly this will be selecting the correct types of
bracket '(...)' or '{...}', both of which are currently in use.

gdb/ChangeLog:

	* cp-valprint.c (cp_print_value_fields): Allow an additional level
	of depth when printing anonymous structs or unions.
	* guile/scm-pretty-print.c (ppscm_print_children): Don't print the
	children if the max-depth is already exceeded.  When printing the
	key of a map, allow one extra level of depth.
	* python/py-prettyprint.c (print_children): Likewise.
	* valprint.c: Add 'c-lang.h' include.
	(PRINT_MAX_DEPTH_DEFAULT): Define.
	(user_print_options): Initialise max_depth field.
	(val_print_scalar_or_string_type_p): New function.
	(val_print): Check to see if the max depth has been reached.
	(show_print_max_depth): New function.
	(_initialize_valprint): Add 'print max-depth' option.
	* valprint.h (struct value_print_options) <max_depth>: New field.
	* NEWS: Document new feature.

gdb/doc/ChangeLog:

	* gdb.texinfo (Print Settings): Document 'print max-depth'.
	* guile.texi (Guile Pretty Printing API): Document that 'print
	max-depth' can effect the display of a values children.
	* python.texi (Pretty Printing API): Likewise.

gdb/testsuite/ChangeLog:

	* gdb.base/max-depth.c: New file.
	* gdb.base/max-depth.exp: New file.
	* gdb.python/py-nested-maps.c: New file.
	* gdb.python/py-nested-maps.exp: New file.
	* gdb.python/py-nested-maps.py: New file.
	* gdb.fortran/max-depth.exp: New file.
	* gdb.fortran/max-depth.f90: New file.
	* lib/gdb.exp (get_print_expr_at_depths): New proc.
---
 gdb/ChangeLog                               |  22 +++
 gdb/NEWS                                    |   9 ++
 gdb/cp-valprint.c                           |  32 +++--
 gdb/doc/ChangeLog                           |   7 +
 gdb/doc/gdb.texinfo                         |  57 ++++++++
 gdb/doc/guile.texi                          |   3 +
 gdb/doc/python.texi                         |   3 +
 gdb/guile/scm-pretty-print.c                |  23 ++-
 gdb/python/py-prettyprint.c                 |  22 ++-
 gdb/testsuite/ChangeLog                     |  12 ++
 gdb/testsuite/gdb.base/max-depth.c          | 209 +++++++++++++++++++++++++++
 gdb/testsuite/gdb.base/max-depth.exp        | 122 ++++++++++++++++
 gdb/testsuite/gdb.fortran/max-depth.exp     |  41 ++++++
 gdb/testsuite/gdb.fortran/max-depth.f90     |  40 ++++++
 gdb/testsuite/gdb.python/py-nested-maps.c   | 122 ++++++++++++++++
 gdb/testsuite/gdb.python/py-nested-maps.exp | 211 ++++++++++++++++++++++++++++
 gdb/testsuite/gdb.python/py-nested-maps.py  | 129 +++++++++++++++++
 gdb/testsuite/lib/gdb.exp                   |  30 ++++
 gdb/valprint.c                              |  66 ++++++++-
 gdb/valprint.h                              |   3 +
 20 files changed, 1148 insertions(+), 15 deletions(-)
 create mode 100644 gdb/testsuite/gdb.base/max-depth.c
 create mode 100644 gdb/testsuite/gdb.base/max-depth.exp
 create mode 100644 gdb/testsuite/gdb.fortran/max-depth.exp
 create mode 100644 gdb/testsuite/gdb.fortran/max-depth.f90
 create mode 100644 gdb/testsuite/gdb.python/py-nested-maps.c
 create mode 100644 gdb/testsuite/gdb.python/py-nested-maps.exp
 create mode 100644 gdb/testsuite/gdb.python/py-nested-maps.py

[2/2] gdb: Introduce 'print max-depth' feature

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