support <:O>: if a label is not found, continue execution after the go-to statement

* this is a SciTECO extension - it's not in TECO-11
* Allows for select-case-like constructs with default-clauses as in
  :Os.^EQa$
    !* default *!
  !s.foo!
    !* ... *!
  !s.bar!
    !* ... *!
* Consistent with nOlabel0,label1,...$ if <n> is out of range.
  Unfortunately this form of computed goto is not applicable when
  "selecting" by strings or non-consecutive integers.
* In order to continue after the <:O> statement, we must keep the
  program counter along with the label we were looking for.
  At the end of the macro, the PC is restored instead of throwing
  an error.
* Since that would be very inefficient in loops - where potentially
  all iterations would result in rescanning till the end of the
  macro - we now store a completed-flag in the goto table.
  If it is set while trying to :O to an unknown label, we can
  just continue execution.

10 files changed, 101 insertions, 39 deletions

diff --git a/TODO b/TODO
index 128fa6a..ddb5b76 100644
--- a/TODO
+++ b/TODO
@@ -729,9 +729,6 @@ Features:
    This would ease subscripting, e.g. to remove the last character:
    0,:Qq-1Qq^Uq$
    There should also be m,nA for consistency.
- * :Olabel$ to avoid throwing an error if label is not defined.
-   This would be very useful when using computed Gotos as select-case
-   like constructs as the code after the Goto would act as a default-clause.
  * Sort order in Q-register autocompletions should be numeric,
    so ^A11 comes after ^A1.
  * FFI interface: There could be a command nFXlib$func$str$
diff --git a/src/core-commands.c b/src/core-commands.c
index 5fe960b..8ce7a24 100644
--- a/src/core-commands.c
+++ b/src/core-commands.c
@@ -633,7 +633,7 @@ teco_state_start_input(teco_machine_main_t *ctx, gunichar chr, GError **error)
 		['$']  = {&teco_state_escape},
 		['!']  = {&teco_state_label},
 		['O']  = {&teco_state_goto,
-		          .modifier_at = TRUE},
+		          .modifier_at = TRUE, .modifier_colon = 1},
 		['^']  = {&teco_state_control,
 		          .modifier_at = TRUE, .modifier_colon = 2},
 		['F']  = {&teco_state_fcommand,
diff --git a/src/error.h b/src/error.h
index b4f92ad..2a12733 100644
--- a/src/error.h
+++ b/src/error.h
@@ -42,6 +42,7 @@ typedef enum {
 	TECO_ERROR_SYNTAX,
 	TECO_ERROR_MODIFIER,
 	TECO_ERROR_ARGEXPECTED,
+	TECO_ERROR_LABEL,
 	TECO_ERROR_CODEPOINT,
 	TECO_ERROR_MOVE,
 	TECO_ERROR_WORDS,
@@ -92,6 +93,14 @@ teco_error_argexpected_set(GError **error, const gchar *cmd)
 }
 
 static inline void
+teco_error_label_set(GError **error, const gchar *name, gsize len)
+{
+	g_autofree gchar *label_printable = teco_string_echo(name, len);
+	g_set_error(error, TECO_ERROR, TECO_ERROR_LABEL,
+	            "Label \"%s\" not found", label_printable);
+}
+
+static inline void
 teco_error_codepoint_set(GError **error, const gchar *cmd)
 {
 	g_set_error(error, TECO_ERROR, TECO_ERROR_CODEPOINT,
diff --git a/src/goto-commands.c b/src/goto-commands.c
index ac98b70..73575ca 100644
--- a/src/goto-commands.c
+++ b/src/goto-commands.c
@@ -38,7 +38,17 @@
 TECO_DECLARE_STATE(teco_state_blockcomment);
 TECO_DECLARE_STATE(teco_state_eolcomment);
 
+/**
+ * In TECO_MODE_PARSE_ONLY_GOTO mode, we remain in parse-only mode
+ * until the given label is encountered.
+ */
 teco_string_t teco_goto_skip_label = {NULL, 0};
+/**
+ * The program counter to restore if the teco_goto_skip_label
+ * is \b not found (after :Olabel$).
+ * If smaller than 0 an error is thrown instead.
+ */
+gssize teco_goto_backup_pc = -1;
 
 /*
  * NOTE: The comma is theoretically not allowed in a label
@@ -68,6 +78,7 @@ teco_state_label_input(teco_machine_main_t *ctx, gunichar chr, GError **error)
 			    !teco_string_cmp(&ctx->goto_label, teco_goto_skip_label.data, teco_goto_skip_label.len)) {
 				teco_undo_string_own(teco_goto_skip_label);
 				memset(&teco_goto_skip_label, 0, sizeof(teco_goto_skip_label));
+				teco_undo_gssize(teco_goto_backup_pc) = -1;
 
 				if (ctx->parent.must_undo)
 					teco_undo_flags(ctx->flags);
@@ -122,6 +133,8 @@ teco_state_goto_done(teco_machine_main_t *ctx, const teco_string_t *str, GError
 	if (!teco_expressions_pop_num_calc(&value, 0, error))
 		return NULL;
 
+	gboolean colon_modified = teco_machine_main_eval_colon(ctx) > 0;
+
 	/*
 	 * Find the comma-separated substring in str indexed by `value`.
 	 */
@@ -142,14 +155,19 @@ teco_state_goto_done(teco_machine_main_t *ctx, const teco_string_t *str, GError
 
 		if (pc >= 0) {
 			ctx->macro_pc = pc;
-		} else {
+		} else if (!ctx->goto_table.complete) {
 			/* skip till label is defined */
 			g_assert(teco_goto_skip_label.len == 0);
 			undo__teco_string_truncate(&teco_goto_skip_label, 0);
 			teco_string_init(&teco_goto_skip_label, label.data, label.len);
+			teco_undo_gssize(teco_goto_backup_pc) = colon_modified ? ctx->macro_pc : -1;
 			if (ctx->parent.must_undo)
 				teco_undo_flags(ctx->flags);
 			ctx->flags.mode = TECO_MODE_PARSE_ONLY_GOTO;
+		} else if (!colon_modified) {
+			/* can happen if we previously executed a colon-modified go-to */
+			teco_error_label_set(error, teco_goto_skip_label.data, teco_goto_skip_label.len);
+			return NULL;
 		}
 	}
 
@@ -164,6 +182,7 @@ gboolean teco_state_goto_insert_completion(teco_machine_main_t *ctx, const teco_
 
 /*$ "O" goto
  * Olabel$ -- Go to label
+ * :Olabel$
  * [n]Olabel0[,label1,...]$
  *
  * Go to <label>.
@@ -186,14 +205,19 @@ gboolean teco_state_goto_insert_completion(teco_machine_main_t *ctx, const teco_
  * Otherwise, parsing continues until the <label>
  * is defined.
  * The command will yield an error if a label has
- * not been defined when the macro or command-line
- * is terminated.
- * In the latter case, the user will not be able to
- * terminate the command-line.
+ * not been defined when the macro is terminated.
+ * When jumping to a non-existent <label> in the
+ * command-line macro, you cannot practically terminate
+ * the command-line until defining the <label>.
  *
  * 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.
+ * When colon-modifying the \fBO\fP command, execution
+ * will continue after the command if the given <label>
+ * isn't found.
+ * This is useful to handle the \(lqdefault\(rq case
+ * when using computed go-tos of the second kind.
  */
 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/goto-commands.h b/src/goto-commands.h
index f4f52d5..45c68e9 100644
--- a/src/goto-commands.h
+++ b/src/goto-commands.h
@@ -16,10 +16,13 @@
  */
 #pragma once
 
+#include <glib.h>
+
 #include "parser.h"
 #include "string-utils.h"
 
 extern teco_string_t teco_goto_skip_label;
+extern gssize teco_goto_backup_pc;
 
 TECO_DECLARE_STATE(teco_state_label);
 TECO_DECLARE_STATE(teco_state_goto);
diff --git a/src/goto.h b/src/goto.h
index eda823f..05c7598 100644
--- a/src/goto.h
+++ b/src/goto.h
@@ -26,10 +26,14 @@
 typedef struct {
 	teco_rb3str_tree_t tree;
 
+	/** Whether to generate undo tokens (unnecessary in macro invocations) */
+	guint must_undo : 1;
+
 	/**
-	 * Whether to generate undo tokens (unnecessary in macro invocations)
+	 * Whether the table is guaranteed to be complete because the entire
+	 * macro has already been parsed.
 	 */
-	gboolean must_undo;
+	guint complete : 1;
 } teco_goto_table_t;
 
 /** @memberof teco_goto_table_t */
@@ -38,6 +42,7 @@ teco_goto_table_init(teco_goto_table_t *ctx, gboolean must_undo)
 {
 	rb3_reset_tree(&ctx->tree);
 	ctx->must_undo = must_undo;
+	ctx->complete = FALSE;
 }
 
 gboolean teco_goto_table_remove(teco_goto_table_t *ctx, const gchar *name, gsize len);
diff --git a/src/parser.c b/src/parser.c
index 6d4cd60..a5e6e4f 100644
--- a/src/parser.c
+++ b/src/parser.c
@@ -186,41 +186,60 @@ teco_execute_macro(const gchar *macro, gsize macro_len,
 
 	GError *tmp_error = NULL;
 
-	if (!teco_machine_main_step(&macro_machine, macro, macro_len, &tmp_error)) {
-		if (!g_error_matches(tmp_error, TECO_ERROR, TECO_ERROR_RETURN)) {
-			/* passes ownership of tmp_error */
-			g_propagate_error(error, tmp_error);
-			goto error_cleanup;
+	for (;;) {
+		if (!teco_machine_main_step(&macro_machine, macro, macro_len, &tmp_error)) {
+			if (!g_error_matches(tmp_error, TECO_ERROR, TECO_ERROR_RETURN)) {
+				/* passes ownership of tmp_error */
+				g_propagate_error(error, tmp_error);
+				goto error_cleanup;
+			}
+			g_error_free(tmp_error);
+
+			/*
+			 * Macro returned - handle like regular
+			 * end of macro, even though some checks
+			 * are unnecessary here.
+			 * macro_pc will still point to the return PC.
+			 */
+			g_assert(macro_machine.parent.current == &teco_state_start);
+
+			/*
+			 * Discard all braces, except the current one.
+			 */
+			if (!teco_expressions_brace_return(parent_brace_level, teco_error_return_args, error))
+				goto error_cleanup;
+
+			/*
+			 * Clean up the loop stack.
+			 * We are allowed to return in loops.
+			 * NOTE: This does not have to be undone.
+			 */
+			g_array_remove_range(teco_loop_stack, macro_machine.loop_stack_fp,
+			                     teco_loop_stack->len - macro_machine.loop_stack_fp);
 		}
-		g_error_free(tmp_error);
 
-		/*
-		 * Macro returned - handle like regular
-		 * end of macro, even though some checks
-		 * are unnecessary here.
-		 * macro_pc will still point to the return PC.
-		 */
-		g_assert(macro_machine.parent.current == &teco_state_start);
+		if (G_LIKELY(teco_goto_backup_pc < 0))
+			break;
 
-		/*
-		 * Discard all braces, except the current one.
-		 */
-		if (!teco_expressions_brace_return(parent_brace_level, teco_error_return_args, error))
-			goto error_cleanup;
+		/* continue after :Olabel$ */
+		macro_machine.macro_pc = teco_goto_backup_pc;
+		/* macro could have ended in a "lookahead" state */
+		macro_machine.parent.current = &teco_state_start;
 
-		/*
-		 * Clean up the loop stack.
-		 * We are allowed to return in loops.
-		 * NOTE: This does not have to be undone.
-		 */
-		g_array_remove_range(teco_loop_stack, macro_machine.loop_stack_fp,
-		                     teco_loop_stack->len - macro_machine.loop_stack_fp);
+		teco_undo_string_own(teco_goto_skip_label);
+		memset(&teco_goto_skip_label, 0, sizeof(teco_goto_skip_label));
+		teco_undo_gssize(teco_goto_backup_pc) = -1;
+
+		if (macro_machine.parent.must_undo)
+			teco_undo_flags(macro_machine.flags);
+		macro_machine.flags.mode = TECO_MODE_NORMAL;
+
+		/* no need to reparse everything in the future */
+		macro_machine.goto_table.complete = TRUE;
 	}
 
 	if (G_UNLIKELY(teco_goto_skip_label.len > 0)) {
-		g_autofree gchar *label_printable = teco_string_echo(teco_goto_skip_label.data, teco_goto_skip_label.len);
-		g_set_error(error, TECO_ERROR, TECO_ERROR_FAILED,
-		            "Label \"%s\" not found", label_printable);
+		teco_error_label_set(error, teco_goto_skip_label.data, teco_goto_skip_label.len);
 		goto error_attach;
 	}
 
diff --git a/src/undo.c b/src/undo.c
index c8b22ab..2048af3 100644
--- a/src/undo.c
+++ b/src/undo.c
@@ -34,6 +34,7 @@ TECO_DEFINE_UNDO_SCALAR(gunichar);
 TECO_DEFINE_UNDO_SCALAR(gint);
 TECO_DEFINE_UNDO_SCALAR(guint);
 TECO_DEFINE_UNDO_SCALAR(gsize);
+TECO_DEFINE_UNDO_SCALAR(gssize);
 TECO_DEFINE_UNDO_SCALAR(teco_int_t);
 TECO_DEFINE_UNDO_SCALAR(gboolean);
 TECO_DEFINE_UNDO_SCALAR(gconstpointer);
diff --git a/src/undo.h b/src/undo.h
index 459fdb0..c236970 100644
--- a/src/undo.h
+++ b/src/undo.h
@@ -182,6 +182,9 @@ TECO_DECLARE_UNDO_SCALAR(guint);
 TECO_DECLARE_UNDO_SCALAR(gsize);
 #define teco_undo_gsize(VAR) (*teco_undo_object_gsize_push(&(VAR)))
 
+TECO_DECLARE_UNDO_SCALAR(gssize);
+#define teco_undo_gssize(VAR) (*teco_undo_object_gssize_push(&(VAR)))
+
 TECO_DECLARE_UNDO_SCALAR(teco_int_t);
 #define teco_undo_int(VAR) (*teco_undo_object_teco_int_t_push(&(VAR)))
 
diff --git a/tests/testsuite.at b/tests/testsuite.at
index 3cca113..0079c38 100644
--- a/tests/testsuite.at
+++ b/tests/testsuite.at
@@ -117,6 +117,7 @@ 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([[:@O/foo/]], 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)