From b3b87f0f8a8091c88461953d686f9772dfb3c4bc Mon Sep 17 00:00:00 2001
From: Jake Leahy <jake@leahy.dev>
Date: Sun, 17 Dec 2023 22:29:46 +1100
Subject: [PATCH] Mark `macros.error` as `.noreturn.` (#23081)

Closes #14329

Marks `macros.error` as `.noreturn` so that it can be used in
expressions. This also fixes the issue that occurred in #19659 where a
stmt that could be an expression (Due to having `discardable` procs at
the end of other branches) would believe a `noreturn` proc is returning
the same type e.g.
```nim
 proc bar(): int {.discardable.} = discard

if true: bar()
else: quit(0) # Says that quit is of type `int` and needs to be used/discarded except it actually has no return type
```
---
 compiler/condsyms.nim        |  1 +
 compiler/semstmts.nim        |  5 +++++
 lib/core/macros.nim          |  7 ++++++-
 tests/casestmt/tcasestmt.nim | 14 ++++++++++++++
 tests/macros/t14329.nim      |  4 ++++
 5 files changed, 30 insertions(+), 1 deletion(-)
 create mode 100644 tests/macros/t14329.nim

diff --git a/compiler/condsyms.nim b/compiler/condsyms.nim
index 5865e5310e..085576c6b2 100644
--- a/compiler/condsyms.nim
+++ b/compiler/condsyms.nim
@@ -157,6 +157,7 @@ proc initDefines*(symbols: StringTableRef) =
   defineSymbol("nimAllowNonVarDestructor")
   defineSymbol("nimHasQuirky")
   defineSymbol("nimHasEnsureMove")
+  defineSymbol("nimHasNoReturnError")
 
   defineSymbol("nimUseStrictDefs")
   defineSymbol("nimHasNolineTooLong")
diff --git a/compiler/semstmts.nim b/compiler/semstmts.nim
index eacda7f9b7..a0eda36d1e 100644
--- a/compiler/semstmts.nim
+++ b/compiler/semstmts.nim
@@ -169,6 +169,11 @@ proc discardCheck(c: PContext, result: PNode, flags: TExprFlags) =
         while n.kind in skipForDiscardable:
           if n.kind == nkTryStmt: n = n[0]
           else: n = n.lastSon
+
+        # Ignore noreturn procs since they don't have a type
+        if n.endsInNoReturn:
+          return
+
         var s = "expression '" & $n & "' is of type '" &
             result.typ.typeToString & "' and has to be used (or discarded)"
         if result.info.line != n.info.line or
diff --git a/lib/core/macros.nim b/lib/core/macros.nim
index 01a654b6c6..fe911ffbf6 100644
--- a/lib/core/macros.nim
+++ b/lib/core/macros.nim
@@ -427,7 +427,12 @@ proc copyNimTree*(n: NimNode): NimNode {.magic: "NCopyNimTree", noSideEffect.} =
       let x = 12
       echo x
 
-proc error*(msg: string, n: NimNode = nil) {.magic: "NError", benign.}
+when defined(nimHasNoReturnError):
+  {.pragma: errorNoReturn, noreturn.}
+else:
+  {.pragma: errorNoReturn.}
+
+proc error*(msg: string, n: NimNode = nil) {.magic: "NError", benign, errorNoReturn.}
   ## Writes an error message at compile time. The optional `n: NimNode`
   ## parameter is used as the source for file and line number information in
   ## the compilation error message.
diff --git a/tests/casestmt/tcasestmt.nim b/tests/casestmt/tcasestmt.nim
index 3a4907494a..aea0c96a42 100644
--- a/tests/casestmt/tcasestmt.nim
+++ b/tests/casestmt/tcasestmt.nim
@@ -298,3 +298,17 @@ proc main(a: uint64) =
 static:
   main(10)
 main(10)
+
+block:
+  # Just needs to compile
+  proc bar(): int {.discardable.} = discard
+
+  proc foo() {.noreturn.} = discard
+
+  case "*"
+  of "*":
+    bar()
+  else:
+    # Make sure this noreturn doesn't
+    # cause the discardable to not discard
+    foo()
diff --git a/tests/macros/t14329.nim b/tests/macros/t14329.nim
new file mode 100644
index 0000000000..b5606424ae
--- /dev/null
+++ b/tests/macros/t14329.nim
@@ -0,0 +1,4 @@
+import macros
+
+macro myMacro(n) =
+  let x = if true: newLit"test" else: error "error", n