From f9e44035e88f8f6ae05062e995f31a4d4e22915b Mon Sep 17 00:00:00 2001
From: Graham Nelson <graham.nelson@mod-langs.ox.ac.uk>
Date: Sun, 10 Apr 2022 09:37:34 +0100
Subject: [PATCH] Fix for Mantis bug 2002

---
 .../Test Problems/PM_UseOptionAtLeastNegative.txt    |  9 +++++++++
 .../_Results_Ideal/PM_UseOptionAtLeastNegative.txt   | 11 +++++++++++
 .../Chapter 3/New Use Option Requests.w              |  2 +-
 .../Chapter 3/Use Option Requests.w                  | 12 ++++++++++--
 4 files changed, 31 insertions(+), 3 deletions(-)
 create mode 100644 inform7/Tests/Test Problems/PM_UseOptionAtLeastNegative.txt
 create mode 100644 inform7/Tests/Test Problems/_Results_Ideal/PM_UseOptionAtLeastNegative.txt

diff --git a/inform7/Tests/Test Problems/PM_UseOptionAtLeastNegative.txt b/inform7/Tests/Test Problems/PM_UseOptionAtLeastNegative.txt
new file mode 100644
index 0000000000..1ee8a4b328
--- /dev/null
+++ b/inform7/Tests/Test Problems/PM_UseOptionAtLeastNegative.txt	
@@ -0,0 +1,9 @@
+Foo is a room.
+Use blurble of at least 0 translates as (- Constant BLURBLE = {N}; -).
+Use blah of at least -10 translates as (- Constant BLAH = {N}; -).
+Include (-
+	[ foo2 x; x = BLURBLE; ];
+-).
+Include (-
+	[ foo x; x = BLAH; ];
+-).
diff --git a/inform7/Tests/Test Problems/_Results_Ideal/PM_UseOptionAtLeastNegative.txt b/inform7/Tests/Test Problems/_Results_Ideal/PM_UseOptionAtLeastNegative.txt
new file mode 100644
index 0000000000..f6cbd31609
--- /dev/null
+++ b/inform7/Tests/Test Problems/_Results_Ideal/PM_UseOptionAtLeastNegative.txt	
@@ -0,0 +1,11 @@
+Inform 7 v10.1.0 has started.
+I've now read your source text, which is 30 words long.
+I've also read Basic Inform by Graham Nelson, which is 7691 words long.
+I've also read English Language by Graham Nelson, which is 2328 words long.
+I've also read Standard Rules by Graham Nelson, which is 32092 words long.
+Problem__ PM_UseOptionAtLeastNegative
+  >--> You wrote 'Use blah of at least -10 translates as (- Constant BLAH =
+    {N}; -)' (source text, line 3): but the minimum possible value is not
+    allowed to be negative, since it describes a quantity which must be 0 or
+    more
+Inform 7 has finished.
diff --git a/inform7/assertions-module/Chapter 3/New Use Option Requests.w b/inform7/assertions-module/Chapter 3/New Use Option Requests.w
index 1e49b10857..bbbafafadb 100644
--- a/inform7/assertions-module/Chapter 3/New Use Option Requests.w	
+++ b/inform7/assertions-module/Chapter 3/New Use Option Requests.w	
@@ -85,7 +85,7 @@ typedef struct use_option {
 	uo->name = GET_RW(<use-setting>, 1);
 	uo->expansion = OP;
 	uo->option_used = FALSE;
-	uo->minimum_setting_value = (N > 0) ? N : -1;
+	uo->minimum_setting_value = (N >= 0) ? N : -1;
 	uo->source_file_scoped = FALSE;
 	uo->notable_option_code = -1;
 	if (<notable-use-option-name>(uo->name)) uo->notable_option_code = <<r>>;
diff --git a/inform7/assertions-module/Chapter 3/Use Option Requests.w b/inform7/assertions-module/Chapter 3/Use Option Requests.w
index 2b9ca0ba8c..9b6ad5e04d 100644
--- a/inform7/assertions-module/Chapter 3/Use Option Requests.w	
+++ b/inform7/assertions-module/Chapter 3/Use Option Requests.w	
@@ -51,13 +51,21 @@ option name is taken from the |...| or |###| as appropriate:
 	... language index                             ==> { TRUE, - }
 
 <use-memory-setting> ::=
-	### of <cardinal-number-unlimited>             ==> { R[1], - }
+	### of <cardinal-number-unlimited>             ==> @<Validate the at-least setting@>
 
 <use-setting> ::=
-	... of at least <cardinal-number-unlimited> |  ==> { R[1], - }
+	... of at least <cardinal-number-unlimited> |  ==> @<Validate the at-least setting@>
 	<definite-article> ...	|                      ==> { -1, - }
 	...                                            ==> { -1, - }
 
+@<Validate the at-least setting@> =
+	if (R[1] < 0)
+		StandardProblems::sentence_problem(Task::syntax_tree(),
+			_p_(PM_UseOptionAtLeastNegative),
+			"the minimum possible value is not allowed to be negative",
+			"since it describes a quantity which must be 0 or more");
+	==> { R[1], - }
+
 @<Set a single use option@> =
 	wording S = Node::get_text(p);
 	if (<use-inter-pipeline>(S))