[flang] Fix minor nits with INCLUDE line recognition

[klausler]

Summary

Fix some problems with INCLUDE line recognition pointed out by some
recently-added tests to the LLVM test suite.

[PeteSteinfeld]

All builds and tests correctly and looks good.

flang/docs/Extensions.md

 * The character length of the `SOURCE=` or `MOLD=` in `ALLOCATE`
   may be distinct from the constant character length, if any,
   of an allocated object.
 * When a name is brought into a scope by multiple ways,
   such as USE-association as well as an `IMPORT` from its host,
   it's an error only if the resolution is ambiguous.
 * An entity may appear in a `DATA` statement before its explicit
   type declaration under `IMPLICIT NONE(TYPE)`.
+* INCLUDE lines can start in any column, can be preceded in
+  fixed form source by a '0' in column 6, can contain spaces
+  between the letters of the word INCLUDE, and can have a
+  numeric character literal kind prefix on the file name.
 
 ### Extensions supported when enabled by options
 
 * C-style backslash escape sequences in quoted CHARACTER literals
   (but not Hollerith) [-fbackslash]
 * Logical abbreviations `.T.`, `.F.`, `.N.`, `.A.`, `.O.`, and `.X.`
   [-flogical-abbreviations]
 * `.XOR.` as a synonym for `.NEQV.` [-fxor-operator]
* f18 does not enforce a blanket prohibition against generic
   interfaces containing a mixture of functions and subroutines.
   Apart from some contexts in which the standard requires all of
   a particular generic interface to have only all functions or
   all subroutines as its specific procedures, we allow both to
   appear, unlike several other Fortran compilers.
   This is especially desirable when two generics of the same
   name are combined due to USE association and the mixture may
   be inadvertent.
+* Since Fortran 90, INCLUDE lines have been allowed to have
+  a numeric kind parameter prefix on the file name.  No other
+  Fortran compiler supports them that I can find.
 
 ## Behavior in cases where the standard is ambiguous or indefinite
 
 * When an inner procedure of a subprogram uses the value or an attribute
   of an undeclared name in a specification expression and that name does
   not appear in the host, it is not clear in the standard whether that
   name is an implicitly typed local variable of the inner procedure or a
   host association with an implicitly typed local variable of the host.

flang/lib/Parser/prescan.cpp

if (*p == '!' || *p == '\n') {
     return IsAtProcess(p) ? p : nullptr;
   } else {
     return nullptr;
   }
 }
 
 std::optional<std::size_t> Prescanner::IsIncludeLine(const char *start) const {
   const char *p{SkipWhiteSpace(start)};
-  for (char ch : "include"s) {
-    if (ToLowerCaseLetter(*p++) != ch) {
+  if (*p == '0' && inFixedForm_ && p == start + 5) {
+    // Accept "     0INCLUDE" in fixed form.
+    p = SkipWhiteSpace(p + 1);
+  }
+  for (const char *q{"include"}; *q; ++q) {
+    if (ToLowerCaseLetter(*p) != *q) {
       return std::nullopt;
     }
+    p = SkipWhiteSpace(p + 1);
+  }
+  if (IsDecimalDigit(*p)) { // accept & ignore a numeric kind prefix
+    for (p = SkipWhiteSpace(p + 1); IsDecimalDigit(*p);
+         p = SkipWhiteSpace(p + 1)) {
+    }
+    if (*p != '_') {
+      return std::nullopt;
+    }
+    p = SkipWhiteSpace(p + 1);
   }
-  p = SkipWhiteSpace(p);
   if (*p == '"' || *p == '\'') {
     return {p - start};
   }
   return std::nullopt;
 }
 
 void Prescanner::FortranInclude(const char *firstQuote) {
   const char *p{firstQuote};
if (InCompilerDirective()) {
     if (col1 == '\t' && nextLine_[1] >= '1' && nextLine_[1] <= '9') {
       tabInCurrentLine_ = true;
       return nextLine_ + 2; // VAX extension
     }
     if (col1 == ' ' && nextLine_[1] == ' ' && nextLine_[2] == ' ' &&
         nextLine_[3] == ' ' && nextLine_[4] == ' ') {
       char col6{nextLine_[5]};
       if (col6 != '\n' && col6 != '\t' && col6 != ' ' && col6 != '0') {
+        if ((col6 == 'i' || col6 == 'I') && IsIncludeLine(nextLine_)) {
+          // It's An INCLUDE line, not a continuation
+        } else {
           return nextLine_ + 6;
         }
       }
+    }
     if (IsImplicitContinuation()) {
       return nextLine_;
     }
   }
   return nullptr; // not a continuation line
 }
 
 const char *Prescanner::FreeFormContinuationLine(bool ampersand) {

flang/test/Parser/Inputs/include-file

+      x = 1

flang/test/Parser/include.f

+! RUN: %flang_fc1 -E -I %S/Inputs %s 2>&1 | FileCheck %s
+      include 'include-file'
+      include "include-file"
+      include 1_'include-file'
+      include 1_"include-file"
+      i n c l u d e 'include-file'
+      INCLUDE 'include-file'
+      I N C L U D E 'include-file'
+include 'include-file'
+include "include-file"
+include 1_'include-file'
+include 1_"include-file"
+i n c l u d e 'include-file'
+INCLUDE 'include-file'
+I N C L U D E 'include-file'
+     0include 'include-file'
+      x = 2
+     include 'include-file'
+      print *, "
+     1include 'not-an-include'
+     2"
+cinclude 'not-an-include'
+*include 'not-an-include'
+!include 'not-an-include'
+c     include 'not-an-include'
+*     include 'not-an-include'
+!     include 'not-an-include'
+      end
+
+!CHECK:#line "{{.*[/\\]}}include-file" 1
+!CHECK:      x = 1
+!CHECK:#line "{{.*[/\\]}}include-file" 1
+!CHECK:      x = 1
+!CHECK:#line "{{.*[/\\]}}include-file" 1
+!CHECK:      x = 1
+!CHECK:#line "{{.*[/\\]}}include-file" 1
+!CHECK:      x = 1
+!CHECK:#line "{{.*[/\\]}}include-file" 1
+!CHECK:      x = 1
+!CHECK:#line "{{.*[/\\]}}include-file" 1
+!CHECK:      x = 1
+!CHECK:#line "{{.*[/\\]}}include-file" 1
+!CHECK:      x = 1
+!CHECK:#line "{{.*[/\\]}}include-file" 1
+!CHECK:      x = 1
+!CHECK:#line "{{.*[/\\]}}include-file" 1
+!CHECK:      x = 1
+!CHECK:#line "{{.*[/\\]}}include-file" 1
+!CHECK:      x = 1
+!CHECK:#line "{{.*[/\\]}}include-file" 1
+!CHECK:      x = 1
+!CHECK:#line "{{.*[/\\]}}include-file" 1
+!CHECK:      x = 1
+!CHECK:#line "{{.*[/\\]}}include-file" 1
+!CHECK:      x = 1
+!CHECK:#line "{{.*[/\\]}}include-file" 1
+!CHECK:      x = 1
+!CHECK:#line "{{.*[/\\]}}include-file" 1
+!CHECK:      x = 1
+!CHECK:#line "{{.*[/\\]}}include.f" 17
+!CHECK:      x = 2
+!CHECK:#line "{{.*[/\\]}}include-file" 1
+!CHECK:      x = 1
+!CHECK:#line "{{.*[/\\]}}include.f" 19
+!CHECK:      print *, "                                                        &
+!CHECK:     &include 'not-an-include'                                          &
+!CHECK:     &"
+!CHECK:      end