[PATCH] Formalise the use of spaces rather than tabs

[John Darrington]

Mention in HACKING that we like spaces rather than tabs in our code, and add a
syntax-check for this.  (This change doesn't fix the things that will cause
this test to fail!)
---
 HACKING | 13 ++++++++++---
 cfg.mk  |  6 ++++++
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/HACKING b/HACKING
index cc524860..8329e371 100644
--- a/HACKING
+++ b/HACKING
@@ -59,9 +59,10 @@ along with GNU poke.  If not, see 
<https://www.gnu.org/licenses/>.
        3.17  Continuous Integration
      4  Coding Style and Conventions
        4.1  Writing C
-         4.1.1  Avoid bool
-         4.1.2  Use _p for Predicates
-         4.1.3  Documenting Functions in Public Headers
+         4.1.1  Avoid Tabs
+         4.1.2  Avoid bool
+         4.1.3  Use _p for Predicates
+         4.1.4  Documenting Functions in Public Headers
        4.2  Writing Poke
        4.3  Writing RAS
      5  Writing Tests
@@ -445,6 +446,12 @@ Additionally, we have a few conventions that we ask you to 
follow when
 hacking poke, in order to keep a coherent style when possible.  These
 are documented in the following subsections.
 
+Avoid Tabs
+..........
+
+Please format your code using spaces.  Tabs (Ascii 9) should not
+appear anywhere except in Makefiles.
+
 Avoid bool
 ..........
 
diff --git a/cfg.mk b/cfg.mk
index d2e6c122..dcce90d4 100644
--- a/cfg.mk
+++ b/cfg.mk
@@ -39,3 +39,9 @@ sc_unitalicised_etc:
        exclude='@i{etc}'                              \
        halt='found unitalicised "etc" in Texinfo source.  Use @i{etc}' \
          $(_sc_search_regexp)
+
+sc_tabs_in_source:
+       @prohibit='     '                    \
+       in_vc_files='\.[chly]$$'                 \
+       halt='found tabs in source.  Use spaces instead.'           \
+       $(_sc_search_regexp)
-- 
2.20.1