fixes #19662; Indent level errored for first line (#19718)

compiler/parser.nim

@@ -2393,6 +2393,10 @@ proc parseAll(p: var Parser): PNode =
     if p.tok.indent != 0:
       parMessage(p, errInvalidIndentation)
 
+proc checkFirstLineIndentation*(p: var Parser) =
+  if p.tok.indent != 0 and p.tok.strongSpaceA > 0:
+    parMessage(p, errInvalidIndentation)
+
 proc parseTopLevelStmt(p: var Parser): PNode =
   ## Implements an iterator which, when called repeatedly, returns the next
   ## top-level statement or emptyNode if end of stream.

compiler/passes.nim

@@ -150,6 +150,7 @@ proc processModule*(graph: ModuleGraph; module: PSym; idgen: IdGenerator;
         processImplicits graph, graph.config.implicitImports, nkImportStmt, a, module
         processImplicits graph, graph.config.implicitIncludes, nkIncludeStmt, a, module
 
+    checkFirstLineIndentation(p)
     while true:
       if graph.stopCompile(): break
       var n = parseTopLevelStmt(p)

compiler/syntaxes.nim

@@ -16,7 +16,7 @@ import
 when defined(nimPreviewSlimSystem):
   import std/[syncio, assertions]
 
-export Parser, parseAll, parseTopLevelStmt, closeParser
+export Parser, parseAll, parseTopLevelStmt, checkFirstLineIndentation, closeParser
 
 type
   FilterKind = enum

tests/parser/t19662.nim

@@ -0,0 +1,6 @@
+                var i: int # bug #19662
+echo i
+
+discard """
+  errormsg: "invalid indentation"
+"""