Extend ‘format’ to translate curved quotes

This is a followup to the recent doc string change, and deals with
diagnostics and the like.  This patch is more conservative than
the doc string change, in that the behavior of ‘format’ changes
only if its first arg contains curved quotes and the user prefers
straight or grave quotes.  (Come to think of it, perhaps we should
be similarly conservative with doc strings too, but that can wait.)
The upside of this conservatism is that existing usage is almost
surely unaffected.  The downside is that we'll eventually have to
change Emacs's format strings to use curved quotes in places where
the user might want curved quotes, but that's a simple and
mechanical translation that I'm willing to do later.  (Bug#21222)
* doc/lispref/help.texi (Keys in Documentation):
Move description of text-quoting-style from here ...
* doc/lispref/strings.texi (Formatting Strings):
... to here, and describe new behavior of ‘format’.
* etc/NEWS: Describe new behavior.
* lisp/calc/calc-help.el (calc-describe-thing):
* lisp/emacs-lisp/derived.el (derived-mode-make-docstring):
* lisp/info.el (Info-find-index-name):
Use ‘concat’ rather than ‘format’ to avoid misinterpretation
of recently-added curved quotes.
* src/doc.c (uLSQM0, uLSQM1, uLSQM2, uRSQM0, uRSQM1, uRSQM2):
Move from here ...
* src/lisp.h: ... to here.
* src/doc.c (text_quoting_style): New function.
(Fsubstitute_command_keys): Use it.
* src/editfns.c (Fformat): Implement new behavior.
* src/lisp.h (enum text_quoting_style): New enum.

1 files changed, 19 insertions, 0 deletions

diff --git a/src/lisp.h b/src/lisp.h
index 2545203a674..d3dcaecd2bb 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -4300,6 +4300,25 @@ extern void set_initial_environment (void);
 extern void syms_of_callproc (void);
 
 /* Defined in doc.c.  */
+enum
+  {
+    /* Named constants for the UTF-8 encodings of U+2018 LEFT SINGLE
+       QUOTATION MARK and U+2019 RIGHT SINGLE QUOTATION MARK.  */
+    uLSQM0 = 0xE2, uLSQM1 = 0x80, uLSQM2 = 0x98,
+    uRSQM0 = 0xE2, uRSQM1 = 0x80, uRSQM2 = 0x99
+  };
+enum text_quoting_style
+  {
+    /* Use curved single quotes ‘like this’.  */
+    CURVE_QUOTING_STYLE,
+
+    /* Use grave accent and apostrophe  `like this'.  */
+    GRAVE_QUOTING_STYLE,
+
+    /* Use apostrophes 'like this'.  */
+    STRAIGHT_QUOTING_STYLE
+  };
+extern enum text_quoting_style text_quoting_style (void);
 extern Lisp_Object read_doc_string (Lisp_Object);
 extern Lisp_Object get_doc_string (Lisp_Object, bool, bool);
 extern void syms_of_doc (void);