Merge pull request #444 from moonbitlang/haoxiang/add-error-codes-index

feat: add error codes index

next/language/error_codes/E0001.md

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+# E0001
+
+There is an internal error occurred to the compiler. Usually this means you have
+discovered a bug in the compiler.
+
+A bug report containing the error description and relevant code would be
+greatly appreciated. You can submit the bug report here:
+
+<https://github.com/moonbitlang/moonbit-docs/issues/new?labels=bug,ICE>

next/language/error_codes/E1001.md

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+# E1001
+
+Unused function.

next/language/error_codes/E1002.md

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+# E1002
+
+Unused variable.

next/language/error_codes/E1003.md

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+# E1003
+
+Unused type declaration.

next/language/error_codes/E1004.md

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+# E1004
+
+Unused abstract type.

next/language/error_codes/E1005.md

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+# E1005
+
+Unused generic type variable.

next/language/error_codes/E1006.md

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+# E1006
+
+Variant is unused.

next/language/error_codes/E1007.md

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+# E1007
+
+Field is never read.

next/language/error_codes/E1008.md

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+# E1008
+
+The modifier is redundant here since field is modifier by default.

next/language/error_codes/E1009.md

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+# E1009
+
+The struct is never constructed.

next/language/error_codes/E1010.md

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+# E1010
+
+Unused pattern.

next/language/error_codes/E1011.md

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+# E1011
+
+Partial match.

next/language/error_codes/E1012.md

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+# E1012
+
+Unreachable code.

next/language/error_codes/E1013.md

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+# E1013
+
+The type of this expression contains unresolved type variables.

next/language/error_codes/E1014.md

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+# E1014
+
+Type name should be capitalized.

next/language/error_codes/E1015.md

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+# E1015
+
+The mutability is never used.

next/language/error_codes/E1016.md

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+# E1016
+
+Parser consistency check failed.

next/language/error_codes/E1018.md

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+# E1018
+
+There is no [continue] in this loop expression, so [loop] is useless here.

next/language/error_codes/E1019.md

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+# E1019
+
+Toplevel declaration is not left aligned.

next/language/error_codes/E1020.md

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+# E1020
+
+Invalid pragma.

next/language/error_codes/E1021.md

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+# E1021
+
+Some arguments of constructor are omitted in pattern.

next/language/error_codes/E1022.md

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+# E1022
+
+Ambiguous block expression.

next/language/error_codes/E1023.md

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+# E1023
+
+The body of this try expression never raises any error.

next/language/error_codes/E1024.md

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+# E1024
+
+The error type of this function is never used.

next/language/error_codes/E1026.md

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+# E1026
+
+The patterns are complete so the usage of `catch!` is useless.

next/language/error_codes/E1027.md

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+# E1027
+
+The syntax is deprecated.

next/language/error_codes/E1028.md

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+# E1028
+
+Unfinished code.

next/language/error_codes/E1029.md

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+# E1029
+
+Unused package.

next/language/error_codes/E1030.md

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+# E1030
+
+The package alias is empty.

next/language/error_codes/E1031.md

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+# E1031
+
+The optional argument is never supplied.

next/language/error_codes/E1032.md

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+# E1032
+
+Default value of optional argument is unused.

next/language/error_codes/E1033.md

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+# E1033
+
+The import value is never used directly.

next/language/error_codes/E1034.md

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+# E1034
+
+The syntax `~label` is deprecated.

next/language/error_codes/E1035.md

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+# E1035
+
+The word is reserved for possible future use.

next/language/error_codes/E1036.md

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+# E1036
+
+The label name shadows a label name that is already in scope.

next/language/error_codes/E1037.md

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+# E1037
+
+The label name is never used.

next/language/error_codes/E1038.md

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+# E1038
+
+Useless guard because the pattern is irrefutable.

next/language/error_codes/E1039.md

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+# E1039
+
+Method name conflicts with another definition.

next/language/error_codes/E1040.md

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+# E1040
+
+Calling this kind of method directly via name(..) is deprecated.

next/language/error_codes/E2000.md

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+# E2000
+
+The usage of function (type, trait, etc.) is flagged with alert. Usually, alert
+message comes with a alert kind and a detailed description of the alert. If you
+are using the function from a library, these alerts are set by the library
+author to provide some more information on the usage of the function
+
+There are some common alerts that you may encounter:
+
+* `deprecated`: indicates the function (type, trait, etc) is deprecated and
+  should not be used or migrate to new APIs.
+* `unsafe`: indicates this API panics, breaks internal invariants, has undefined
+  behavior under some circumstances. The concrete semantics of this kind of
+  alerts may be different across packages, and please consult the documentation
+  or the author of these packages for further details.
+
+## Erroneous example
+
+```moonbit
+/// @alert deprecated "Use `greet` instead"
+fn greeting() -> String {
+  "Hello!"
+}
+
+fn greet(name~ : String = "") -> String {
+  if name != "" {
+    "Hello!"
+  } else {
+    "Hello, \{name}!"
+  }
+}
+
+fn main() -> Unit {
+  println(greeting())
+  //      ^~~~~~~~ Warning (Alert deprecated): Use `greet` instead(2000)
+}
+```
+
+## Suggestion
+
+One way to fix the alert, is to change your code as suggested by the message (like `deprecated`):
+
+```moonbit
+// ... code in the example above ...
+fn main() -> Unit {
+  println(greet(name="world"))
+}
+```
+
+If you clearly know what you are doing and would like to suppress the alert, you can change the `moon.pkg.json` file for packages where you would like to disable **this kind of alert**. For example:
+
+```moonbit
+{
+  // ... other fields in the file
+  "alert-list": "-deprecated"
+}
+```
+
+NOTE: There is no way to disable alerts for a line/file.

next/language/error_codes/E3001.md

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+# E3001
+
+Lexing error

next/language/error_codes/E3002.md

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+# E3002
+
+Parse error

next/language/error_codes/E3003.md

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+# E3003
+
+`init` and `main` function must have no arguments and no return value.
+
+## Erroneous example
+
+```moonbit
+fn main() -> Unit {
+  println("Hello, world!")
+}
+```
+
+## Suggestion
+
+Remove the argument list and return type annotation, as:
+
+```moonbit
+fn main {
+  println("Hello, world!")
+}
+```

next/language/error_codes/E3004.md

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+# E3004
+
+Missing parameters list. Add `()` after the name of the function if it takes 0
+parameter.
+
+## Erroneous example
+
+```moonbit
+fn greet {
+  println("Hello, world!")
+}
+```
+
+## Suggestion
+
+Add `()` after the function name.
+
+```moonbit
+fn greet() {
+  println("Hello, world!")
+}
+```

next/language/error_codes/E3005.md

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+# E3005
+
+There is no such visibility for the entity (function/type/trait/...).
+
+Usually, this means that you put an `priv` visibility modifier on a entity is
+by-default private.
+
+See the [Access
+Control](https://docs.moonbitlang.com/en/latest/language/packages.html#access-control)
+section of [MoonBit Language
+Documentation](https://docs.moonbitlang.com/en/latest/language/index.html) for a
+detailed explanaion on the visibility in MoonBit.
+
+## Erroneous example
+
+```moonbit
+priv let value = 3
+```
+
+## Suggestion
+
+Remove the visibility modifier from the definition of the entity:
+
+```moonbit
+let value = 3 // This is already `priv` by default.
+```

next/language/error_codes/E3006.md

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+# E3006
+
+There is no individual visibility control fro enum constructors.
+
+Usually, this means that you put an `priv` or `pub` visibility modifier on a enum constructor.
+
+## Erroneous example
+
+```moonbit
+enum A {
+  priv A1
+  pub A2
+}
+```
+
+## Suggestion
+
+Remove the visibility modifier from the definition of the enum constructor:
+
+```moonbit
+enum A {
+  A1
+  A2
+}
+```

next/language/error_codes/E3007.md

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+# E3007
+
+Wrong location of `..` in pattern match. Put `..` at the end of the pattern.
+
+## Erroneous example
+
+```moonbit
+let {a, .., c} = s
+```
+
+## Suggestion
+
+```moonbit
+let {a, c, ..} = s
+```

next/language/error_codes/E3008.md

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+# E3008
+
+There are multiple `..` patterns in array pattern. Remove until there is only one `..` pattern in array pattern.
+
+## Erroneous example
+
+```moonbit
+let [fst, .., .., snd] = array
+```
+
+## Suggestion
+
+Remove the extra `..` pattern.
+
+```moonbit
+let [fst, .., snd] = array
+```