Fix regression in checking module type

src/compile/compile_package.zig

@@ -789,6 +789,7 @@ pub const PackageEnv = struct {
         // Canonicalize
         var czer = try Can.init(env, parse_ast, module_envs_out);
         try czer.canonicalizeFile();
+        try czer.validateForChecking();
         czer.deinit();
 
         // Type check using the SAME module_envs_map

test/snapshots/default_app_no_main.md

@@ -8,9 +8,22 @@ type=file
 helper = |x| x + 1
 ~~~
 # EXPECTED
-NIL
+MISSING MAIN! FUNCTION - default_app_no_main.md:1:1:1:19
 # PROBLEMS
-NIL
+**MISSING MAIN! FUNCTION**
+Default app modules must have a `main!` function.
+
+No `main!` function was found.
+
+Add a main! function like:
+`main! = |arg| { ... }`
+**default_app_no_main.md:1:1:1:19:**
+```roc
+helper = |x| x + 1
+```
+^^^^^^^^^^^^^^^^^^
+
+
 # TOKENS
 ~~~zig
 LowerIdent,OpAssign,OpBar,LowerIdent,OpBar,LowerIdent,OpPlus,Int,

test/snapshots/default_app_wrong_arity.md

@@ -11,6 +11,7 @@ main! = |arg1, arg2| {
 ~~~
 # EXPECTED
 UNUSED VARIABLE - default_app_wrong_arity.md:1:16:1:20
+MAIN! SHOULD TAKE 1 ARGUMENT - default_app_wrong_arity.md:1:1:3:2
 # PROBLEMS
 **UNUSED VARIABLE**
 Variable `arg2` is not used anywhere in your code.
@@ -24,6 +25,21 @@ main! = |arg1, arg2| {
                ^^^^
 
 
+**MAIN! SHOULD TAKE 1 ARGUMENT**
+`main!` is defined but has the wrong number of arguments. `main!` should take 1 argument.
+
+Found `2` arguments.
+
+Change it to:
+`main! = |arg| { ... }`
+**default_app_wrong_arity.md:1:1:3:2:**
+```roc
+main! = |arg1, arg2| {
+    arg1
+}
+```
+
+
 # TOKENS
 ~~~zig
 LowerIdent,OpAssign,OpBar,LowerIdent,Comma,LowerIdent,OpBar,OpenCurly,

test/snapshots/fuzz_crash/fuzz_crash_001.md

@@ -11,6 +11,7 @@ mo|%
 PARSE ERROR - fuzz_crash_001.md:1:1:1:3
 PARSE ERROR - fuzz_crash_001.md:1:3:1:4
 PARSE ERROR - fuzz_crash_001.md:1:4:1:5
+MISSING MAIN! FUNCTION - fuzz_crash_001.md:1:1:1:5
 # PROBLEMS
 **PARSE ERROR**
 A parsing error occurred: `statement_unexpected_token`
@@ -45,6 +46,20 @@ mo|%
    ^
 
 
+**MISSING MAIN! FUNCTION**
+Default app modules must have a `main!` function.
+
+No `main!` function was found.
+
+Add a main! function like:
+`main! = |arg| { ... }`
+**fuzz_crash_001.md:1:1:1:5:**
+```roc
+mo|%
+```
+^^^^
+
+
 # TOKENS
 ~~~zig
 LowerIdent,OpBar,OpPercent,

test/snapshots/fuzz_crash/fuzz_crash_002.md

@@ -20,6 +20,7 @@ PARSE ERROR - fuzz_crash_002.md:1:21:1:23
 PARSE ERROR - fuzz_crash_002.md:1:23:1:24
 PARSE ERROR - fuzz_crash_002.md:1:24:1:25
 MALFORMED TYPE - fuzz_crash_002.md:1:6:1:7
+MISSING MAIN! FUNCTION - fuzz_crash_002.md:1:1:1:25
 # PROBLEMS
 **UNEXPECTED TOKEN IN TYPE ANNOTATION**
 The token **;** is not expected in a type annotation.
@@ -152,6 +153,20 @@ modu:;::::::::::::::le[%
      ^
 
 
+**MISSING MAIN! FUNCTION**
+Default app modules must have a `main!` function.
+
+No `main!` function was found.
+
+Add a main! function like:
+`main! = |arg| { ... }`
+**fuzz_crash_002.md:1:1:1:25:**
+```roc
+modu:;::::::::::::::le[%
+```
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+
 # TOKENS
 ~~~zig
 LowerIdent,OpColon,MalformedUnknownToken,OpDoubleColon,OpDoubleColon,OpDoubleColon,OpDoubleColon,OpDoubleColon,OpDoubleColon,OpDoubleColon,LowerIdent,OpenSquare,OpPercent,

test/snapshots/fuzz_crash/fuzz_crash_003.md

@@ -13,6 +13,7 @@ PARSE ERROR - fuzz_crash_003.md:1:1:1:2
 PARSE ERROR - fuzz_crash_003.md:1:3:1:4
 PARSE ERROR - fuzz_crash_003.md:1:4:1:6
 PARSE ERROR - fuzz_crash_003.md:1:6:1:6
+MISSING MAIN! FUNCTION - fuzz_crash_003.md:1:1:1:6
 # PROBLEMS
 **UNCLOSED STRING**
 This string is missing a closing quote.
@@ -68,6 +69,20 @@ This is an unexpected parsing error. Please check your syntax.
      ^
 
 
+**MISSING MAIN! FUNCTION**
+Default app modules must have a `main!` function.
+
+No `main!` function was found.
+
+Add a main! function like:
+`main! = |arg| { ... }`
+**fuzz_crash_003.md:1:1:1:6:**
+```roc
+= "te
+```
+^^^^^
+
+
 # TOKENS
 ~~~zig
 OpAssign,StringStart,StringPart,StringEnd,

test/snapshots/fuzz_crash/fuzz_crash_004.md

@@ -9,6 +9,7 @@ F
 ~~~
 # EXPECTED
 PARSE ERROR - fuzz_crash_004.md:2:1:2:1
+MISSING MAIN! FUNCTION - fuzz_crash_004.md:1:1:1:2
 # PROBLEMS
 **PARSE ERROR**
 Type applications require parentheses around their type arguments.
@@ -33,6 +34,20 @@ Other valid examples:
 ^
 
 
+**MISSING MAIN! FUNCTION**
+Default app modules must have a `main!` function.
+
+No `main!` function was found.
+
+Add a main! function like:
+`main! = |arg| { ... }`
+**fuzz_crash_004.md:1:1:1:2:**
+```roc
+F
+```
+^
+
+
 # TOKENS
 ~~~zig
 UpperIdent,

test/snapshots/fuzz_crash/fuzz_crash_005.md

@@ -9,6 +9,7 @@ modu
 ~~~
 # EXPECTED
 PARSE ERROR - fuzz_crash_005.md:1:1:1:5
+MISSING MAIN! FUNCTION - fuzz_crash_005.md:1:1:1:5
 # PROBLEMS
 **PARSE ERROR**
 A parsing error occurred: `statement_unexpected_token`
@@ -21,6 +22,20 @@ modu
 ^^^^
 
 
+**MISSING MAIN! FUNCTION**
+Default app modules must have a `main!` function.
+
+No `main!` function was found.
+
+Add a main! function like:
+`main! = |arg| { ... }`
+**fuzz_crash_005.md:1:1:1:5:**
+```roc
+modu
+```
+^^^^
+
+
 # TOKENS
 ~~~zig
 LowerIdent,

test/snapshots/fuzz_crash/fuzz_crash_007.md

@@ -11,6 +11,7 @@ ff8.8.d
 PARSE ERROR - fuzz_crash_007.md:1:1:1:4
 PARSE ERROR - fuzz_crash_007.md:1:4:1:6
 PARSE ERROR - fuzz_crash_007.md:1:6:1:8
+MISSING MAIN! FUNCTION - fuzz_crash_007.md:1:1:1:8
 # PROBLEMS
 **PARSE ERROR**
 A parsing error occurred: `statement_unexpected_token`
@@ -45,6 +46,20 @@ ff8.8.d
      ^^
 
 
+**MISSING MAIN! FUNCTION**
+Default app modules must have a `main!` function.
+
+No `main!` function was found.
+
+Add a main! function like:
+`main! = |arg| { ... }`
+**fuzz_crash_007.md:1:1:1:8:**
+```roc
+ff8.8.d
+```
+^^^^^^^
+
+
 # TOKENS
 ~~~zig
 LowerIdent,NoSpaceDotInt,NoSpaceDotLowerIdent,

test/snapshots/fuzz_crash/fuzz_crash_008.md

@@ -12,6 +12,7 @@ ASCII CONTROL CHARACTER - :0:0:0:0
 PARSE ERROR - fuzz_crash_008.md:1:1:1:2
 PARSE ERROR - fuzz_crash_008.md:1:3:1:4
 PARSE ERROR - fuzz_crash_008.md:1:4:1:5
+MISSING MAIN! FUNCTION - fuzz_crash_008.md:1:1:1:5
 # PROBLEMS
 **ASCII CONTROL CHARACTER**
 ASCII control characters are not allowed in Roc source code.
@@ -51,6 +52,20 @@ This is an unexpected parsing error. Please check your syntax.
    ^
 
 
+**MISSING MAIN! FUNCTION**
+Default app modules must have a `main!` function.
+
+No `main!` function was found.
+
+Add a main! function like:
+`main! = |arg| { ... }`
+**fuzz_crash_008.md:1:1:1:5:**
+```roc
+||1
+```
+^^^^
+
+
 # TOKENS
 ~~~zig
 OpBar,OpBar,Int,

test/snapshots/fuzz_crash/fuzz_crash_009.md

@@ -19,6 +19,7 @@ PARSE ERROR - fuzz_crash_009.md:1:3:1:4
 PARSE ERROR - fuzz_crash_009.md:1:4:1:5
 PARSE ERROR - fuzz_crash_009.md:1:5:1:6
 PARSE ERROR - fuzz_crash_009.md:2:6:2:7
+MISSING MAIN! FUNCTION - fuzz_crash_009.md:1:2:6:12
 # PROBLEMS
 **UNCLOSED STRING**
 This string is missing a closing quote.
@@ -85,6 +86,24 @@ This is an unexpected parsing error. Please check your syntax.
      ^
 
 
+**MISSING MAIN! FUNCTION**
+Default app modules must have a `main!` function.
+
+No `main!` function was found.
+
+Add a main! function like:
+`main! = |arg| { ... }`
+**fuzz_crash_009.md:1:2:6:12:**
+```roc
+ f{o,
+     ]
+
+foo =
+
+    "onmo %
+```
+
+
 # TOKENS
 ~~~zig
 LowerIdent,OpenCurly,LowerIdent,Comma,

test/snapshots/fuzz_crash/fuzz_crash_010.md

@@ -18,6 +18,7 @@ PARSE ERROR - fuzz_crash_010.md:1:2:1:3
 PARSE ERROR - fuzz_crash_010.md:1:3:1:4
 PARSE ERROR - fuzz_crash_010.md:1:4:1:5
 PARSE ERROR - fuzz_crash_010.md:2:6:2:7
+MISSING MAIN! FUNCTION - fuzz_crash_010.md:1:1:5:35
 # PROBLEMS
 **ASCII CONTROL CHARACTER**
 ASCII control characters are not allowed in Roc source code.
@@ -90,6 +91,23 @@ This is an unexpected parsing error. Please check your syntax.
      ^
 
 
+**MISSING MAIN! FUNCTION**
+Default app modules must have a `main!` function.
+
+No `main!` function was found.
+
+Add a main! function like:
+`main! = |arg| { ... }`
+**fuzz_crash_010.md:1:1:5:35:**
+```roc
+H{o,
+    ]
+foo =
+
+    "on        (string 'onmo %')))
+```
+
+
 # TOKENS
 ~~~zig
 UpperIdent,OpenCurly,LowerIdent,Comma,

test/snapshots/fuzz_crash/fuzz_crash_012.md

@@ -15,6 +15,7 @@ PARSE ERROR - fuzz_crash_012.md:1:4:1:5
 PARSE ERROR - fuzz_crash_012.md:1:5:1:6
 PARSE ERROR - fuzz_crash_012.md:1:6:1:16
 PARSE ERROR - fuzz_crash_012.md:1:16:1:17
+MISSING MAIN! FUNCTION - fuzz_crash_012.md:1:1:1:17
 # PROBLEMS
 **PARSE ERROR**
 A parsing error occurred: `statement_unexpected_token`
@@ -93,6 +94,20 @@ This is an unexpected parsing error. Please check your syntax.
                ^
 
 
+**MISSING MAIN! FUNCTION**
+Default app modules must have a `main!` function.
+
+No `main!` function was found.
+
+Add a main! function like:
+`main! = |arg| { ... }`
+**fuzz_crash_012.md:1:1:1:17:**
+```roc
+||(|(l888888888|
+```
+^^^^^^^^^^^^^^^^
+
+
 # TOKENS
 ~~~zig
 OpBar,OpBar,NoSpaceOpenRound,OpBar,NoSpaceOpenRound,LowerIdent,OpBar,

test/snapshots/fuzz_crash/fuzz_crash_013.md

@@ -10,6 +10,7 @@ type=file
 # EXPECTED
 PARSE ERROR - fuzz_crash_013.md:1:1:1:2
 PARSE ERROR - fuzz_crash_013.md:1:2:1:3
+MISSING MAIN! FUNCTION - fuzz_crash_013.md:1:1:1:3
 # PROBLEMS
 **PARSE ERROR**
 A parsing error occurred: `statement_unexpected_token`
@@ -33,6 +34,20 @@ This is an unexpected parsing error. Please check your syntax.
  ^
 
 
+**MISSING MAIN! FUNCTION**
+Default app modules must have a `main!` function.
+
+No `main!` function was found.
+
+Add a main! function like:
+`main! = |arg| { ... }`
+**fuzz_crash_013.md:1:1:1:3:**
+```roc
+0{
+```
+^^
+
+
 # TOKENS
 ~~~zig
 Int,OpenCurly,

test/snapshots/fuzz_crash/fuzz_crash_014.md

@@ -14,6 +14,7 @@ PARSE ERROR - fuzz_crash_014.md:1:1:1:3
 PARSE ERROR - fuzz_crash_014.md:1:3:1:5
 PARSE ERROR - fuzz_crash_014.md:2:1:2:6
 PARSE ERROR - fuzz_crash_014.md:3:1:3:5
+MISSING MAIN! FUNCTION - fuzz_crash_014.md:1:1:3:5
 # PROBLEMS
 **PARSE ERROR**
 A parsing error occurred: `statement_unexpected_token`
@@ -59,6 +60,21 @@ This is an unexpected parsing error. Please check your syntax.
 ^^^^
 
 
+**MISSING MAIN! FUNCTION**
+Default app modules must have a `main!` function.
+
+No `main!` function was found.
+
+Add a main! function like:
+`main! = |arg| { ... }`
+**fuzz_crash_014.md:1:1:3:5:**
+```roc
+0b.0
+0bu22
+0u22
+```
+
+
 # TOKENS
 ~~~zig
 MalformedNumberNoDigits,NoSpaceDotInt,

test/snapshots/fuzz_crash/fuzz_crash_015.md

@@ -18,6 +18,7 @@ PARSE ERROR - fuzz_crash_015.md:2:1:2:4
 PARSE ERROR - fuzz_crash_015.md:3:1:3:4
 PARSE ERROR - fuzz_crash_015.md:3:4:3:6
 PARSE ERROR - fuzz_crash_015.md:4:1:4:3
+MISSING MAIN! FUNCTION - fuzz_crash_015.md:1:1:4:3
 # PROBLEMS
 **LEADING ZERO**
 Numbers cannot have leading zeros.
@@ -90,6 +91,22 @@ This is an unexpected parsing error. Please check your syntax.
 ^^
 
 
+**MISSING MAIN! FUNCTION**
+Default app modules must have a `main!` function.
+
+No `main!` function was found.
+
+Add a main! function like:
+`main! = |arg| { ... }`
+**fuzz_crash_015.md:1:1:4:3:**
+```roc
+0o0.0
+0_0
+0u8.0
+0_
+```
+
+
 # TOKENS
 ~~~zig
 Int,NoSpaceDotInt,

test/snapshots/fuzz_crash/fuzz_crash_016.md

@@ -10,6 +10,7 @@ type=file
 # EXPECTED
 PARSE ERROR - fuzz_crash_016.md:1:1:1:2
 PARSE ERROR - fuzz_crash_016.md:1:2:1:3
+MISSING MAIN! FUNCTION - fuzz_crash_016.md:1:1:1:3
 # PROBLEMS
 **PARSE ERROR**
 A parsing error occurred: `statement_unexpected_token`
@@ -33,6 +34,20 @@ This is an unexpected parsing error. Please check your syntax.
  ^
 
 
+**MISSING MAIN! FUNCTION**
+Default app modules must have a `main!` function.
+
+No `main!` function was found.
+
+Add a main! function like:
+`main! = |arg| { ... }`
+**fuzz_crash_016.md:1:1:1:3:**
+```roc
+0|
+```
+^^
+
+
 # TOKENS
 ~~~zig
 Int,OpBar,

test/snapshots/fuzz_crash/fuzz_crash_017.md

@@ -11,6 +11,7 @@ foo = "hello ${namF
 # EXPECTED
 PARSE ERROR - fuzz_crash_017.md:2:7:2:8
 UNRECOGNIZED SYNTAX - fuzz_crash_017.md:2:7:2:20
+MISSING MAIN! FUNCTION - fuzz_crash_017.md:1:1:2:20
 # PROBLEMS
 **PARSE ERROR**
 A parsing error occurred: `string_expected_close_interpolation`
@@ -34,6 +35,20 @@ foo = "hello ${namF
 
 This might be a syntax error, an unsupported language feature, or a typo.
 
+**MISSING MAIN! FUNCTION**
+Default app modules must have a `main!` function.
+
+No `main!` function was found.
+
+Add a main! function like:
+`main! = |arg| { ... }`
+**fuzz_crash_017.md:1:1:2:20:**
+```roc
+me = "luc"
+foo = "hello ${namF
+```
+
+
 # TOKENS
 ~~~zig
 LowerIdent,OpAssign,StringStart,StringPart,StringEnd,

test/snapshots/fuzz_crash/fuzz_crash_018.md

@@ -12,6 +12,7 @@ type=file
 PARSE ERROR - fuzz_crash_018.md:1:1:1:2
 PARSE ERROR - fuzz_crash_018.md:2:1:2:3
 UNDECLARED TYPE - fuzz_crash_018.md:1:5:1:6
+MISSING MAIN! FUNCTION - fuzz_crash_018.md:1:1:2:3
 # PROBLEMS
 **PARSE ERROR**
 A parsing error occurred: `statement_unexpected_token`
@@ -46,6 +47,20 @@ This type is referenced here:
     ^
 
 
+**MISSING MAIN! FUNCTION**
+Default app modules must have a `main!` function.
+
+No `main!` function was found.
+
+Add a main! function like:
+`main! = |arg| { ... }`
+**fuzz_crash_018.md:1:1:2:3:**
+```roc
+0 b:S
+.R
+```
+
+
 # TOKENS
 ~~~zig
 Int,LowerIdent,OpColon,UpperIdent,

test/snapshots/fuzz_crash/fuzz_crash_021.md

@@ -20,6 +20,7 @@ PARSE ERROR - fuzz_crash_021.md:1:16:1:16
 PARSE ERROR - fuzz_crash_021.md:3:1:3:5
 PARSE ERROR - fuzz_crash_021.md:4:1:4:1
 MALFORMED TYPE - fuzz_crash_021.md:3:14:3:15
+TYPE MODULE MISSING MATCHING TYPE - fuzz_crash_021.md:1:1:3:15
 # PROBLEMS
 **UNCLOSED STRING**
 This string is missing a closing quote.
@@ -141,6 +142,23 @@ Pair(a, b+ : (
              ^
 
 
+**TYPE MODULE MISSING MATCHING TYPE**
+Type modules must have a type declaration matching the module name.
+
+This file is named `fuzz_crash_021`.roc, but no top-level type declaration named `fuzz_crash_021` was found.
+
+Add either:
+`fuzz_crash_021 := ...` (nominal type)
+or:
+`fuzz_crash_021 : ...` (type alias)
+**fuzz_crash_021.md:1:1:3:15:**
+```roc
+Fli/main.roc" }
+
+Pair(a, b+ : (
+```
+
+
 # TOKENS
 ~~~zig
 UpperIdent,OpSlash,LowerIdent,NoSpaceDotLowerIdent,StringStart,StringPart,StringEnd,

test/snapshots/fuzz_crash/fuzz_crash_031.md

@@ -18,6 +18,7 @@ PARSE ERROR - fuzz_crash_031.md:1:7:1:8
 PARSE ERROR - fuzz_crash_031.md:4:1:4:6
 UNEXPECTED TOKEN IN EXPRESSION - fuzz_crash_031.md:4:10:4:11
 UNRECOGNIZED SYNTAX - fuzz_crash_031.md:4:10:4:11
+MISSING MAIN! FUNCTION - fuzz_crash_031.md:1:1:4:11
 # PROBLEMS
 **UNCLOSED SINGLE QUOTE**
 This single-quoted literal is missing a closing quote.
@@ -95,6 +96,22 @@ vavar t= '
 
 This might be a syntax error, an unsupported language feature, or a typo.
 
+**MISSING MAIN! FUNCTION**
+Default app modules must have a `main!` function.
+
+No `main!` function was found.
+
+Add a main! function like:
+`main! = |arg| { ... }`
+**fuzz_crash_031.md:1:1:4:11:**
+```roc
+mule []
+
+#el
+vavar t= '
+```
+
+
 # TOKENS
 ~~~zig
 LowerIdent,OpenSquare,CloseSquare,

test/snapshots/fuzz_crash/fuzz_crash_038.md

@@ -10,6 +10,7 @@ type=file
 # EXPECTED
 PARSE ERROR - fuzz_crash_038.md:1:1:1:2
 PARSE ERROR - fuzz_crash_038.md:1:2:1:8
+MISSING MAIN! FUNCTION - fuzz_crash_038.md:1:1:1:13
 # PROBLEMS
 **PARSE ERROR**
 A parsing error occurred: `statement_unexpected_token`
@@ -33,6 +34,20 @@ This is an unexpected parsing error. Please check your syntax.
  ^^^^^^
 
 
+**MISSING MAIN! FUNCTION**
+Default app modules must have a `main!` function.
+
+No `main!` function was found.
+
+Add a main! function like:
+`main! = |arg| { ... }`
+**fuzz_crash_038.md:1:1:1:13:**
+```roc
+*import B as
+```
+^^^^^^^^^^^^
+
+
 # TOKENS
 ~~~zig
 OpStar,KwImport,UpperIdent,KwAs,

test/snapshots/fuzz_crash/fuzz_crash_064.md

@@ -8,9 +8,22 @@ type=file
 
 ~~~
 # EXPECTED
-NIL
+MISSING MAIN! FUNCTION - fuzz_crash_064.md:2:1:2:1
 # PROBLEMS
-NIL
+**MISSING MAIN! FUNCTION**
+Default app modules must have a `main!` function.
+
+No `main!` function was found.
+
+Add a main! function like:
+`main! = |arg| { ... }`
+**fuzz_crash_064.md:2:1:2:1:**
+```roc
+
+```
+^
+
+
 # TOKENS
 ~~~zig
 EndOfFile,

test/snapshots/fuzz_crash/fuzz_crash_079.md

@@ -9,9 +9,22 @@ type=file
 b:r
 ~~~
 # EXPECTED
-NIL
+MISSING MAIN! FUNCTION - fuzz_crash_079.md:2:1:2:4
 # PROBLEMS
-NIL
+**MISSING MAIN! FUNCTION**
+Default app modules must have a `main!` function.
+
+No `main!` function was found.
+
+Add a main! function like:
+`main! = |arg| { ... }`
+**fuzz_crash_079.md:2:1:2:4:**
+```roc
+b:r
+```
+^^^
+
+
 # TOKENS
 ~~~zig
 LowerIdent,OpColon,LowerIdent,

test/snapshots/fuzz_crash/fuzz_hang_001.md

@@ -10,6 +10,7 @@ type=file
 # EXPECTED
 PARSE ERROR - fuzz_hang_001.md:1:1:1:2
 PARSE ERROR - fuzz_hang_001.md:1:3:1:4
+MISSING MAIN! FUNCTION - fuzz_hang_001.md:1:1:1:4
 # PROBLEMS
 **PARSE ERROR**
 A parsing error occurred: `statement_unexpected_token`
@@ -33,6 +34,20 @@ This is an unexpected parsing error. Please check your syntax.
   ^
 
 
+**MISSING MAIN! FUNCTION**
+Default app modules must have a `main!` function.
+
+No `main!` function was found.
+
+Add a main! function like:
+`main! = |arg| { ... }`
+**fuzz_hang_001.md:1:1:1:4:**
+```roc
+0 (
+```
+^^^
+
+
 # TOKENS
 ~~~zig
 Int,OpenRound,

test/snapshots/nominal/nominal_associated_vs_module.md

@@ -14,9 +14,29 @@ useBar : Foo.Bar
 useBar = Something
 ~~~
 # EXPECTED
-NIL
+TYPE MODULE MISSING MATCHING TYPE - nominal_associated_vs_module.md:1:1:7:19
 # PROBLEMS
-NIL
+**TYPE MODULE MISSING MATCHING TYPE**
+Type modules must have a type declaration matching the module name.
+
+This file is named `nominal_associated_vs_module`.roc, but no top-level type declaration named `nominal_associated_vs_module` was found.
+
+Add either:
+`nominal_associated_vs_module := ...` (nominal type)
+or:
+`nominal_associated_vs_module : ...` (type alias)
+**nominal_associated_vs_module.md:1:1:7:19:**
+```roc
+Foo := [Whatever].{
+    Bar := [Something]
+}
+
+# This should resolve to the local Foo.Bar, not try to import from a Foo module
+useBar : Foo.Bar
+useBar = Something
+```
+
+
 # TOKENS
 ~~~zig
 UpperIdent,OpColonEqual,OpenSquare,UpperIdent,CloseSquare,Dot,OpenCurly,

test/snapshots/some_folder/002.md

@@ -16,6 +16,7 @@ PARSE ERROR - 002.md:1:1:1:3
 PARSE ERROR - 002.md:1:4:1:6
 PARSE ERROR - 002.md:1:7:1:8
 PARSE ERROR - 002.md:1:8:1:9
+MISSING MAIN! FUNCTION - 002.md:1:1:5:12
 # PROBLEMS
 **PARSE ERROR**
 A parsing error occurred: `statement_unexpected_token`
@@ -61,6 +62,23 @@ This is an unexpected parsing error. Please check your syntax.
        ^
 
 
+**MISSING MAIN! FUNCTION**
+Default app modules must have a `main!` function.
+
+No `main!` function was found.
+
+Add a main! function like:
+`main! = |arg| { ... }`
+**002.md:1:1:5:12:**
+```roc
+@2 := {}
+
+foo = "one"
+
+bar = "two"
+```
+
+
 # TOKENS
 ~~~zig
 OpaqueName,OpColonEqual,OpenCurly,CloseCurly,

test/snapshots/type_module/WrongName.md

@@ -8,9 +8,24 @@ type=file
 SomeOtherName := [A, B]
 ~~~
 # EXPECTED
-NIL
+TYPE MODULE MISSING MATCHING TYPE - WrongName.md:1:1:1:24
 # PROBLEMS
-NIL
+**TYPE MODULE MISSING MATCHING TYPE**
+Type modules must have a type declaration matching the module name.
+
+This file is named `WrongName`.roc, but no top-level type declaration named `WrongName` was found.
+
+Add either:
+`WrongName := ...` (nominal type)
+or:
+`WrongName : ...` (type alias)
+**WrongName.md:1:1:1:24:**
+```roc
+SomeOtherName := [A, B]
+```
+^^^^^^^^^^^^^^^^^^^^^^^
+
+
 # TOKENS
 ~~~zig
 UpperIdent,OpColonEqual,OpenSquare,UpperIdent,Comma,UpperIdent,CloseSquare,

test/snapshots/type_module/no_type_no_main.md

@@ -8,9 +8,22 @@ type=file
 x = 5
 ~~~
 # EXPECTED
-NIL
+MISSING MAIN! FUNCTION - no_type_no_main.md:1:1:1:6
 # PROBLEMS
-NIL
+**MISSING MAIN! FUNCTION**
+Default app modules must have a `main!` function.
+
+No `main!` function was found.
+
+Add a main! function like:
+`main! = |arg| { ... }`
+**no_type_no_main.md:1:1:1:6:**
+```roc
+x = 5
+```
+^^^^^
+
+
 # TOKENS
 ~~~zig
 LowerIdent,OpAssign,Int,