[erlang-patches] [PATCH] Fix indentation of record fields in Emacs

[Tomas Abrahamsson]

In some situations, the indentation of record fields in Emacs was
strange. This example below shows how Emacs previously would indent
two similar pieces of code very differently:

    some_function_with_a_very_long_name() ->
        #'a-long-record-name-like-it-sometimes-is-with-asn.1-records'{
                                         field1=a,
                                         field2=b}.

    x() ->
        #some_record_name{
       field1=a,
       field2=b}.

This changes the indentation to be like below for both cases:

    some_function() ->
        #some_record{
           field1=a,
           field2=b}.
---
 lib/tools/emacs/erlang.el         |   58 +++++++++++++++++++++++++++++-------
 lib/tools/emacs/test.erl.indented |   38 ++++++++++++++++++++++++
 lib/tools/emacs/test.erl.orig     |   38 ++++++++++++++++++++++++
 3 files changed, 122 insertions(+), 12 deletions(-)

diff --git a/lib/tools/emacs/erlang.el b/lib/tools/emacs/erlang.el
index bc7a190..2f6c7f5 100644
--- a/lib/tools/emacs/erlang.el
+++ b/lib/tools/emacs/erlang.el
@@ -2986,18 +2986,52 @@ This assumes that the preceding expression is either simple
     (forward-sexp (- arg))
     (let ((col (current-column)))
       (skip-chars-backward " \t")
-      ;; Needed to match the colon in "'foo':'bar'".
-      (if (not (memq (preceding-char) '(?# ?:)))
-          col
-        ;; Special hack to handle: (note line break)
-        ;; [#myrecord{
-        ;;  foo = foo}]
-        (or
-         (ignore-errors
-           (backward-char 1)
-           (forward-sexp -1)
-           (current-column))
-         col)))))
+      ;; Special hack to handle: (note line break)
+      ;; [#myrecord{
+      ;;  foo = foo}]
+      ;; where the call (forward-sexp -1) will fail when point is at the `#'.
+      (or
+       (ignore-errors
+	 ;; Needed to match the colon in "'foo':'bar'".
+	 (cond ((eq (preceding-char) ?:)
+		(backward-char 1)
+		(forward-sexp -1)
+		(current-column))
+	       ((eq  (preceding-char) ?#)
+		;; We may now be at:
+		;; - either a construction of a new record
+		;; - or update of a record, in which case we want
+		;;   the column of the expression to be updated.
+		;;
+		;; To see which of the two cases we are at, we first
+		;; move an expression backwards, check for keywords,
+		;; then immediately an expression forwards.  Moving
+		;; backwards skips past tokens like `,' or `->', but
+		;; when moving forwards again, we won't skip past such
+		;; tokens.  We use this: if, after having moved
+		;; forwards, we're back where we started, then it was
+		;; a record update.
+		;; The check for keywords is to detect cases like:
+		;;   case Something of #record_construction{...}
+		(backward-char 1)
+		(let ((record-start (point))
+		      (record-start-col (current-column)))
+		  (forward-sexp -1)
+		  (let ((preceding-expr-col (current-column))
+			;; white space definition according to erl_scan
+			(white-space "\000-\040\200-\240"))
+		    (if (erlang-at-keyword)
+			;; The (forward-sexp -1) call moved past a keyword
+			(1+ record-start-col)
+		      (forward-sexp 1)
+		      (skip-chars-forward white-space record-start)
+		      ;; Are we back where we started?  If so, it was an update.
+		      (if (= (point) record-start)
+			    preceding-expr-col
+			(goto-char record-start)
+			(1+ (current-column)))))))
+	       (t col)))
+       col))))
 
 (defun erlang-indent-parenthesis (stack-position) 
   (let ((previous (erlang-indent-find-preceding-expr)))
diff --git a/lib/tools/emacs/test.erl.indented b/lib/tools/emacs/test.erl.indented
index 2948ccf..e0593c6 100644
--- a/lib/tools/emacs/test.erl.indented
+++ b/lib/tools/emacs/test.erl.indented
@@ -657,3 +657,41 @@ indent_comprehensions() ->
 foo() ->
     [#foo{
 	foo = foo}].
+
+%% Record indentation
+some_function_with_a_very_long_name() ->
+    #'a-long-record-name-like-it-sometimes-is-with-asn.1-records'{
+       field1=a,
+       field2=b},
+    case dummy_function_with_a_very_very_long_name(x) of
+	#'a-long-record-name-like-it-sometimes-is-with-asn.1-records'{
+	   field1=a,
+	   field2=b} ->
+	    ok;
+	Var = #'a-long-record-name-like-it-sometimes-is-with-asn.1-records'{
+		 field1=a,
+		 field2=b} ->
+	    Var#'a-long-record-name-like-it-sometimes-is-with-asn.1-records'{
+	      field1=a,
+	      field2=b};
+	#xyz{
+	   a=1,
+	   b=2} ->
+	    ok
+    end.
+
+another_function_with_a_very_very_long_name() ->
+    #rec{
+       field1=1,
+       field2=1}.
+
+some_function_name_xyz(xyzzy, #some_record{
+				 field1=Field1,
+				 field2=Field2}) ->
+    SomeVariable = f(#'Some-long-record-name'{
+			field_a = 1,
+			'inter-xyz-parameters' =
+			    #'Some-other-very-long-record-name'{
+			       field2 = Field1,
+			       field2 = Field2}}),
+    {ok, SomeVariable}.
diff --git a/lib/tools/emacs/test.erl.orig b/lib/tools/emacs/test.erl.orig
index 1221c56..69356ac 100644
--- a/lib/tools/emacs/test.erl.orig
+++ b/lib/tools/emacs/test.erl.orig
@@ -657,3 +657,41 @@ ok.
 foo() ->
 [#foo{
 foo = foo}].
+
+%% Record indentation
+some_function_with_a_very_long_name() ->
+ #'a-long-record-name-like-it-sometimes-is-with-asn.1-records'{
+ field1=a,
+ field2=b},
+ case dummy_function_with_a_very_very_long_name(x) of
+ #'a-long-record-name-like-it-sometimes-is-with-asn.1-records'{
+ field1=a,
+ field2=b} ->
+ ok;
+ Var = #'a-long-record-name-like-it-sometimes-is-with-asn.1-records'{
+ field1=a,
+ field2=b} ->
+ Var#'a-long-record-name-like-it-sometimes-is-with-asn.1-records'{
+ field1=a,
+ field2=b};
+ #xyz{
+ a=1,
+ b=2} ->
+ ok
+ end.
+
+another_function_with_a_very_very_long_name() ->
+ #rec{
+ field1=1,
+ field2=1}.
+
+some_function_name_xyz(xyzzy, #some_record{
+ field1=Field1,
+ field2=Field2}) ->
+ SomeVariable = f(#'Some-long-record-name'{
+ field_a = 1,
+ 'inter-xyz-parameters' =
+ #'Some-other-very-long-record-name'{
+ field2 = Field1,
+ field2 = Field2}}),
+ {ok, SomeVariable}.
-- 
1.7.5.4