the computed go-to command (O) is now 0-indexed and all invalid indexes and empty labels are ignored

* This has long been a TECO-11 incompatibility.
* The first label in a list has index 0, i.e. `1Ofoo,bar$` jumps to label `!bar!`.
  Consequently 0 is also implied, so `Olabel$` continues to do what you expect.
* `0Ofoo$` was previously also jumping to `!foo!` which was inconsistent:
  All invalid indexes should do nothing, i.e. execution continues after the go-to command.
* Fixed handling of empty labels as in `1Ofoo,,bar$` - execution should also continue
  after the command.
  This eases writing "default" clauses immediately after the go-to.
* The ED hook values now also begin at 0, so most existing ED hook macros should
  continue to work.
* Similarily, the mouse events returned by -EJ also begin at 0 now,
  so fnkeys.tes continues to work as expected.
* It's still very possible of course that this breaks existing code.

7 files changed, 50 insertions, 25 deletions

diff --git a/doc/sciteco.7.template b/doc/sciteco.7.template
index 9f0557e..066deb7 100644
--- a/doc/sciteco.7.template
+++ b/doc/sciteco.7.template
@@ -1262,12 +1262,12 @@ stack are discarded.
 This way, \fPED\fP hooks should not interfere with
 the stack-semantics of commands triggering them.
 .LP
-Possible arguments to the \(lqED\(rq macro begin with 1 and
+Possible arguments to the \(lqED\(rq macro begin with 0 and
 are defined consecutively so the macro can branch to the
 operation using a computed goto.
 The different values are defined as follows:
 .TP
-.B 1
+.B 0
 A file has been \fBadded\fP to the buffer ring.
 It may or may not already exist in the file system.
 This file is \*(ST's current document when this hook
@@ -1275,7 +1275,7 @@ executes.
 Scintilla lexing may be configured in this hook \(em it
 usually only has to be done once.
 .TP
-.B 2
+.B 1
 A buffer has been \fBedited\fP (made the current file).
 This hook is not executed when a file is freshly added
 to the buffer ring, since this can be simulated easily
@@ -1283,13 +1283,13 @@ by branching within the \(lqED\(rq macro.
 In this hook you may want to define language-specific
 auxiliary macros, for instance.
 .TP
-.B 3
+.B 2
 A buffer is about to be \fBclosed\fP (removed from the
 buffer ring).
 The buffer that is about to be closed, is still the
 current document when this hook runs.
 .TP
-.B 4
+.B 3
 \*(ST is about to \fBquit\fP, i.e. exit normally.
 This is \*(ST's equivalent of
 .BR atexit (3)
@@ -2185,11 +2185,13 @@ in classic TECOs.
 .
 .SS Gotos and Labels
 .
-The most basic flow control command in \*(ST is the Go-to command.
+An important flow control command in \*(ST is the Go-to command.
 Since it is really an ordinary command, exceptional only in setting
 the program counter and influencing parsing, it is described in this
 document's command reference.
-\*(ST can perform simple unconditional and computed gotos.
+\*(ST can perform simple unconditional and computed gotos
+which are just as powerful as switch-case statements in other
+languages.
 .LP
 .SCITECO_TOPIC "!" label
 Labels are symbolic and are defined with the following syntax:
diff --git a/src/core-commands.c b/src/core-commands.c
index 6d0a3dc..5fe960b 100644
--- a/src/core-commands.c
+++ b/src/core-commands.c
@@ -2142,13 +2142,13 @@ teco_state_ecommand_flags(teco_machine_main_t *ctx, GError **error)
  * Type of the last mouse event (\fBread-only\fP).
  * One of the following values will be returned:
  * .RS
- * .  IP 1: 4
+ * .  IP 0: 4
  * Some button has been pressed
- * .  IP 2:
+ * .  IP 1:
  * Some button has been released
- * .  IP 3:
+ * .  IP 2:
  * Scroll up
- * .  IP 4:
+ * .  IP 3:
  * Scroll down
  * .RE
  * .IP -2:
diff --git a/src/goto-commands.c b/src/goto-commands.c
index d95886d..ac98b70 100644
--- a/src/goto-commands.c
+++ b/src/goto-commands.c
@@ -24,6 +24,7 @@
 #include <glib.h>
 
 #include "sciteco.h"
+#include "error.h"
 #include "string-utils.h"
 #include "expressions.h"
 #include "parser.h"
@@ -110,15 +111,22 @@ teco_state_goto_done(teco_machine_main_t *ctx, const teco_string_t *str, GError
 	if (ctx->flags.mode > TECO_MODE_NORMAL)
 		return &teco_state_start;
 
+	if (!str->len) {
+		/* you can still write @O/,/, though... */
+		g_set_error_literal(error, TECO_ERROR, TECO_ERROR_FAILED,
+		                    "No labels given for <O>");
+		return NULL;
+	}
+
 	teco_int_t value;
-	if (!teco_expressions_pop_num_calc(&value, 1, error))
+	if (!teco_expressions_pop_num_calc(&value, 0, error))
 		return NULL;
 
 	/*
 	 * Find the comma-separated substring in str indexed by `value`.
 	 */
 	teco_string_t label = {NULL, 0};
-	while (value > 0) {
+	while (value >= 0) {
 		label.data = label.data ? label.data+label.len+1 : str->data;
 		const gchar *p = label.data ? memchr(label.data, ',', str->len - (label.data - str->data)) : NULL;
 		label.len = p ? p - label.data : str->len - (label.data - str->data);
@@ -129,7 +137,7 @@ teco_state_goto_done(teco_machine_main_t *ctx, const teco_string_t *str, GError
 			break;
 	}
 
-	if (value == 0) {
+	if (value < 0 && label.len > 0) {
 		gssize pc = teco_goto_table_find(&ctx->goto_table, label.data, label.len);
 
 		if (pc >= 0) {
@@ -156,19 +164,22 @@ gboolean teco_state_goto_insert_completion(teco_machine_main_t *ctx, const teco_
 
 /*$ "O" goto
  * Olabel$ -- Go to label
- * [n]Olabel1[,label2,...]$
+ * [n]Olabel0[,label1,...]$
  *
  * Go to <label>.
  * The simple go-to command is a special case of the
  * computed go-to command.
  * A comma-separated list of labels may be specified
  * in the string argument.
- * The label to jump to is selected by <n> (1 is <label1>,
- * 2 is <label2>, etc.).
- * If <n> is omitted, 1 is implied.
+ * The label to jump to is selected by <n> (0 is <label0>,
+ * 1 is <label1>, etc.).
+ * If <n> is omitted, 0 is implied.
+ * Computed go-tos can be used like switch-case statements
+ * other languages.
  *
  * If the label selected by <n> is does not exist in the
- * list of labels, the command does nothing.
+ * list of labels or is empty, the command does nothing
+ * and execution continues normally.
  * Label definitions are cached in a table, so that
  * if the label to go to has already been defined, the
  * go-to command will jump immediately.
@@ -179,6 +190,10 @@ gboolean teco_state_goto_insert_completion(teco_machine_main_t *ctx, const teco_
  * is terminated.
  * In the latter case, the user will not be able to
  * terminate the command-line.
+ *
+ * String building constructs are enabled in \fBO\fP
+ * which allows for a second kind of computed go-to,
+ * where the label name contains the value to select.
  */
 TECO_DEFINE_STATE_EXPECTSTRING(teco_state_goto,
 	.process_edit_cmd_cb = (teco_state_process_edit_cmd_cb_t)teco_state_goto_process_edit_cmd,
diff --git a/src/interface.h b/src/interface.h
index c0c41bd..9531d37 100644
--- a/src/interface.h
+++ b/src/interface.h
@@ -155,7 +155,7 @@ gboolean teco_interface_is_interrupted(void);
 
 typedef struct {
 	enum {
-		TECO_MOUSE_PRESSED = 1,
+		TECO_MOUSE_PRESSED = 0,
 		TECO_MOUSE_RELEASED,
 		TECO_MOUSE_SCROLLUP,
 		TECO_MOUSE_SCROLLDOWN
diff --git a/src/qreg.c b/src/qreg.c
index 332b5f6..d49a4d6 100644
--- a/src/qreg.c
+++ b/src/qreg.c
@@ -1334,10 +1334,10 @@ teco_ed_hook(teco_ed_hook_t type, GError **error)
 	       teco_expressions_brace_close(error);
 
 	static const gchar *const type2name[] = {
-		[TECO_ED_HOOK_ADD-1]   = "ADD",
-		[TECO_ED_HOOK_EDIT-1]  = "EDIT",
-		[TECO_ED_HOOK_CLOSE-1] = "CLOSE",
-		[TECO_ED_HOOK_QUIT-1]  = "QUIT"
+		[TECO_ED_HOOK_ADD]	= "ADD",
+		[TECO_ED_HOOK_EDIT]	= "EDIT",
+		[TECO_ED_HOOK_CLOSE]	= "CLOSE",
+		[TECO_ED_HOOK_QUIT]	= "QUIT"
 	};
 
 error_add_frame:
diff --git a/src/qreg.h b/src/qreg.h
index 2b970aa..6daaff3 100644
--- a/src/qreg.h
+++ b/src/qreg.h
@@ -239,7 +239,7 @@ gboolean teco_qreg_stack_pop(teco_qreg_t *qreg, GError **error);
 void teco_qreg_stack_clear(void);
 
 typedef enum {
-	TECO_ED_HOOK_ADD = 1,
+	TECO_ED_HOOK_ADD = 0,
 	TECO_ED_HOOK_EDIT,
 	TECO_ED_HOOK_CLOSE,
 	TECO_ED_HOOK_QUIT
diff --git a/tests/testsuite.at b/tests/testsuite.at
index 3728723..3cca113 100644
--- a/tests/testsuite.at
+++ b/tests/testsuite.at
@@ -114,6 +114,14 @@ TE_CHECK([[3<%a:>-3"N(0/0)' $]], 0, ignore, ignore)
 TE_CHECK([[3<%a :F>(0/0):>-3"N(0/0)' $]], 0, ignore, ignore)
 AT_CLEANUP
 
+AT_SETUP([Gotos and labels])
+TE_CHECK([[@O//]], 1, ignore, ignore)
+TE_CHECK([[^^XUq @O/s.^EUq/ (0/0) !s.X!]], 0, ignore, ignore)
+TE_CHECK([[1@O/foo,bar/ (0/0) !bar!]], 0, ignore, ignore)
+# No-op gotos
+TE_CHECK([[-1@O/foo/ 1@O/foo/ @O/,foo/]], 0, ignore, ignore)
+AT_CLEANUP
+
 AT_SETUP([String arguments])
 TE_CHECK([[Ifoo^Q]]TE_ESCAPE[[(0/0)]]TE_ESCAPE, 0, ignore, ignore)
 TE_CHECK([[@I"foo^Q"(0/0)"]], 0, ignore, ignore)