From 5af3e15dd58cf3053ff23936efb0dfc790c02ded Mon Sep 17 00:00:00 2001
From: Jonathan Coates <git@squiddev.cc>
Date: Tue, 28 May 2024 20:16:32 +0100
Subject: [PATCH] Nicer lexer error for "!"

---
 .../modules/main/cc/internal/syntax/errors.lua  | 17 +++++++++++++++++
 .../modules/main/cc/internal/syntax/lexer.lua   |  3 +++
 .../modules/cc/internal/syntax/lexer_spec.md    | 11 +++++++++++
 3 files changed, 31 insertions(+)

diff --git a/projects/core/src/main/resources/data/computercraft/lua/rom/modules/main/cc/internal/syntax/errors.lua b/projects/core/src/main/resources/data/computercraft/lua/rom/modules/main/cc/internal/syntax/errors.lua
index c425a26dc..ea5cf5d1d 100644
--- a/projects/core/src/main/resources/data/computercraft/lua/rom/modules/main/cc/internal/syntax/errors.lua
+++ b/projects/core/src/main/resources/data/computercraft/lua/rom/modules/main/cc/internal/syntax/errors.lua
@@ -284,6 +284,23 @@ function errors.wrong_ne(start_pos, end_pos)
     }
 end
 
+--[[- `!` was used instead of `not`.
+
+@tparam number start_pos The start position of the token.
+@tparam number end_pos The end position of the token.
+@return The resulting parse error.
+]]
+function errors.wrong_not(start_pos, end_pos)
+    expect(1, start_pos, "number")
+    expect(2, end_pos, "number")
+
+    return {
+        "Unexpected character.",
+        annotate(start_pos, end_pos),
+        "Tip: Replace this with " .. code("not") .. " to negate a boolean.",
+    }
+end
+
 --[[- An unexpected character was used.
 
 @tparam number pos The position of this character.
diff --git a/projects/core/src/main/resources/data/computercraft/lua/rom/modules/main/cc/internal/syntax/lexer.lua b/projects/core/src/main/resources/data/computercraft/lua/rom/modules/main/cc/internal/syntax/lexer.lua
index 0b9d45a7e..9faf3b5a9 100644
--- a/projects/core/src/main/resources/data/computercraft/lua/rom/modules/main/cc/internal/syntax/lexer.lua
+++ b/projects/core/src/main/resources/data/computercraft/lua/rom/modules/main/cc/internal/syntax/lexer.lua
@@ -327,6 +327,9 @@ local function lex_token(context, str, pos)
             elseif contents == "!=" or contents == "<>" then
                 context.report(errors.wrong_ne, pos, end_pos)
                 return tokens.NE, end_pos
+            elseif contents == "!" then
+                context.report(errors.wrong_not, pos, end_pos)
+                return tokens.NOT, end_pos
             end
         end
 
diff --git a/projects/core/src/test/resources/test-rom/spec/modules/cc/internal/syntax/lexer_spec.md b/projects/core/src/test/resources/test-rom/spec/modules/cc/internal/syntax/lexer_spec.md
index a0049c367..c6e983566 100644
--- a/projects/core/src/test/resources/test-rom/spec/modules/cc/internal/syntax/lexer_spec.md
+++ b/projects/core/src/test/resources/test-rom/spec/modules/cc/internal/syntax/lexer_spec.md
@@ -265,6 +265,7 @@ if a != b then end
 if a ~= b then end
 if a && b then end
 if a || b then end
+if ! a then end
 ```
 
 ```txt
@@ -307,6 +308,16 @@ Tip: Replace this with or to check if either value is true.
 4:9-4:9 IDENT b
 4:11-4:14 THEN then
 4:16-4:18 END end
+5:1-5:2 IF if
+Unexpected character.
+   |
+ 5 | if ! a then end
+   |    ^
+Tip: Replace this with not to negate a boolean.
+5:4-5:4 NOT !
+5:6-5:6 IDENT a
+5:8-5:11 THEN then
+5:13-5:15 END end
 ```
 
 For entirely unknown glyphs we should just give up and return an `ERROR` token.