Rewrite FMLexer to use nullptr for errors

This CL rewrites how FMLexer returns errors, instead of having a flag
that gets flipped and needs to be checked, it now returns nullptr for
NextToken() when an error occurs. The Lexer's behaviour has also been
changed to only return nullptr once an error has occurred, instead of
advancing the lexing on further calls.

FMParse now checks the returned value from the lexer instead of
testing the error flag on the parser object. For any operation that
might cause the error state of the parser to change, i.e. consuming a
token, an error check has been added. In the event this check fails
the related function returns nullptr. This will cause the parse to
short circuit and exit.

BUG=pdfium:814

Change-Id: I669012c4732c18d13009be7cd7bf1ae682950904
Reviewed-on: https://pdfium-review.googlesource.com/8950
Commit-Queue: Ryan Harrison <rharrison@chromium.org>
Reviewed-by: (OOO Jul 28 - Aug 8) dsinclair <dsinclair@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>

1 files changed, 71 insertions, 65 deletions

diff --git a/xfa/fxfa/fm2js/cxfa_fmlexer.cpp b/xfa/fxfa/fm2js/cxfa_fmlexer.cpp
index 5ae8a6f40b..d217587e66 100644
--- a/xfa/fxfa/fm2js/cxfa_fmlexer.cpp
+++ b/xfa/fxfa/fm2js/cxfa_fmlexer.cpp
@@ -156,12 +156,15 @@ CXFA_FMLexer::CXFA_FMLexer(const CFX_WideStringC& wsFormCalc)
 
 CXFA_FMLexer::~CXFA_FMLexer() {}
 
-CXFA_FMToken* CXFA_FMLexer::NextToken() {
+std::unique_ptr<CXFA_FMToken> CXFA_FMLexer::NextToken() {
+  if (m_lexer_error)
+    return nullptr;
+
   m_token = pdfium::MakeUnique<CXFA_FMToken>(m_current_line);
   while (m_cursor <= m_end && *m_cursor) {
     if (!IsFormCalcCharacter(*m_cursor)) {
-      m_lexer_error = true;
-      return m_token.get();
+      RaiseError();
+      return nullptr;
     }
 
     switch (*m_cursor) {
@@ -180,7 +183,7 @@ CXFA_FMToken* CXFA_FMLexer::NextToken() {
       case '"': {
         m_token->m_type = TOKstring;
         AdvanceForString();
-        return m_token.get();
+        return std::move(m_token);
       }
       case '0':
       case '1':
@@ -194,119 +197,119 @@ CXFA_FMToken* CXFA_FMLexer::NextToken() {
       case '9': {
         m_token->m_type = TOKnumber;
         AdvanceForNumber();
-        return m_token.get();
+        return std::move(m_token);
       }
       case '=':
         ++m_cursor;
         if (m_cursor > m_end) {
           m_token->m_type = TOKassign;
-          return m_token.get();
+          return std::move(m_token);
         }
 
-        if (IsFormCalcCharacter(*m_cursor)) {
-          if (*m_cursor == '=') {
-            m_token->m_type = TOKeq;
-            ++m_cursor;
-          } else {
-            m_token->m_type = TOKassign;
-          }
+        if (!IsFormCalcCharacter(*m_cursor)) {
+          RaiseError();
+          return nullptr;
+        }
+        if (*m_cursor == '=') {
+          m_token->m_type = TOKeq;
+          ++m_cursor;
         } else {
-          m_lexer_error = true;
+          m_token->m_type = TOKassign;
         }
-        return m_token.get();
+        return std::move(m_token);
       case '<':
         ++m_cursor;
         if (m_cursor > m_end) {
           m_token->m_type = TOKlt;
-          return m_token.get();
+          return std::move(m_token);
         }
 
-        if (IsFormCalcCharacter(*m_cursor)) {
-          if (*m_cursor == '=') {
-            m_token->m_type = TOKle;
-            ++m_cursor;
-          } else if (*m_cursor == '>') {
-            m_token->m_type = TOKne;
-            ++m_cursor;
-          } else {
-            m_token->m_type = TOKlt;
-          }
+        if (!IsFormCalcCharacter(*m_cursor)) {
+          RaiseError();
+          return nullptr;
+        }
+        if (*m_cursor == '=') {
+          m_token->m_type = TOKle;
+          ++m_cursor;
+        } else if (*m_cursor == '>') {
+          m_token->m_type = TOKne;
+          ++m_cursor;
         } else {
-          m_lexer_error = true;
+          m_token->m_type = TOKlt;
         }
-        return m_token.get();
+        return std::move(m_token);
       case '>':
         ++m_cursor;
         if (m_cursor > m_end) {
           m_token->m_type = TOKgt;
-          return m_token.get();
+          return std::move(m_token);
         }
 
-        if (IsFormCalcCharacter(*m_cursor)) {
-          if (*m_cursor == '=') {
-            m_token->m_type = TOKge;
-            ++m_cursor;
-          } else {
-            m_token->m_type = TOKgt;
-          }
+        if (!IsFormCalcCharacter(*m_cursor)) {
+          RaiseError();
+          return nullptr;
+        }
+        if (*m_cursor == '=') {
+          m_token->m_type = TOKge;
+          ++m_cursor;
         } else {
-          m_lexer_error = true;
+          m_token->m_type = TOKgt;
         }
-        return m_token.get();
+        return std::move(m_token);
       case ',':
         m_token->m_type = TOKcomma;
         ++m_cursor;
-        return m_token.get();
+        return std::move(m_token);
       case '(':
         m_token->m_type = TOKlparen;
         ++m_cursor;
-        return m_token.get();
+        return std::move(m_token);
       case ')':
         m_token->m_type = TOKrparen;
         ++m_cursor;
-        return m_token.get();
+        return std::move(m_token);
       case '[':
         m_token->m_type = TOKlbracket;
         ++m_cursor;
-        return m_token.get();
+        return std::move(m_token);
       case ']':
         m_token->m_type = TOKrbracket;
         ++m_cursor;
-        return m_token.get();
+        return std::move(m_token);
       case '&':
         ++m_cursor;
         m_token->m_type = TOKand;
-        return m_token.get();
+        return std::move(m_token);
       case '|':
         ++m_cursor;
         m_token->m_type = TOKor;
-        return m_token.get();
+        return std::move(m_token);
       case '+':
         ++m_cursor;
         m_token->m_type = TOKplus;
-        return m_token.get();
+        return std::move(m_token);
       case '-':
         ++m_cursor;
         m_token->m_type = TOKminus;
-        return m_token.get();
+        return std::move(m_token);
       case '*':
         ++m_cursor;
         m_token->m_type = TOKmul;
-        return m_token.get();
+        return std::move(m_token);
       case '/': {
         ++m_cursor;
         if (m_cursor > m_end) {
           m_token->m_type = TOKdiv;
-          return m_token.get();
+          return std::move(m_token);
         }
 
         if (!IsFormCalcCharacter(*m_cursor)) {
-          m_lexer_error = true;
-          return m_token.get();
+          RaiseError();
+          return nullptr;
         }
         if (*m_cursor != '/') {
           m_token->m_type = TOKdiv;
-          return m_token.get();
+          return std::move(m_token);
         }
         AdvanceForComment();
         break;
@@ -315,12 +318,12 @@ CXFA_FMToken* CXFA_FMLexer::NextToken() {
         ++m_cursor;
         if (m_cursor > m_end) {
           m_token->m_type = TOKdot;
-          return m_token.get();
+          return std::move(m_token);
         }
 
         if (!IsFormCalcCharacter(*m_cursor)) {
-          m_lexer_error = true;
-          return m_token.get();
+          RaiseError();
+          return nullptr;
         }
 
         if (*m_cursor == '.') {
@@ -339,7 +342,7 @@ CXFA_FMToken* CXFA_FMLexer::NextToken() {
         } else {
           m_token->m_type = TOKdot;
         }
-        return m_token.get();
+        return std::move(m_token);
       case 0x09:
       case 0x0B:
       case 0x0C:
@@ -348,11 +351,11 @@ CXFA_FMToken* CXFA_FMLexer::NextToken() {
         break;
       default: {
         if (!IsInitialIdentifierCharacter(*m_cursor)) {
-          m_lexer_error = true;
-          return m_token.get();
+          RaiseError();
+          return nullptr;
         }
         AdvanceForIdentifier();
-        return m_token.get();
+        return std::move(m_token);
       }
     }
   }
@@ -360,7 +363,7 @@ CXFA_FMToken* CXFA_FMLexer::NextToken() {
   // If there isn't currently a token type then mark it EOF.
   if (m_token->m_type == TOKreserver)
     m_token->m_type = TOKeof;
-  return m_token.get();
+  return std::move(m_token);
 }
 
 void CXFA_FMLexer::AdvanceForNumber() {
@@ -369,7 +372,7 @@ void CXFA_FMLexer::AdvanceForNumber() {
   if (m_cursor)
     wcstod(const_cast<wchar_t*>(m_cursor), &end);
   if (end && FXSYS_iswalpha(*end)) {
-    m_lexer_error = true;
+    RaiseError();
     return;
   }
 
@@ -406,8 +409,7 @@ void CXFA_FMLexer::AdvanceForString() {
   }
 
   // Didn't find the end of the string.
-  m_token->m_string = CFX_WideStringC(start, (m_cursor - start));
-  m_lexer_error = true;
+  RaiseError();
 }
 
 void CXFA_FMLexer::AdvanceForIdentifier() {
@@ -415,8 +417,7 @@ void CXFA_FMLexer::AdvanceForIdentifier() {
   ++m_cursor;
   while (m_cursor <= m_end && *m_cursor) {
     if (!IsFormCalcCharacter(*m_cursor)) {
-      m_token->m_string = CFX_WideStringC(start, (m_cursor - start));
-      m_lexer_error = true;
+      RaiseError();
       return;
     }
 
@@ -432,6 +433,11 @@ void CXFA_FMLexer::AdvanceForIdentifier() {
 void CXFA_FMLexer::AdvanceForComment() {
   m_cursor++;
   while (m_cursor <= m_end && *m_cursor) {
+    if (!IsFormCalcCharacter(*m_cursor)) {
+      RaiseError();
+      return;
+    }
+
     if (*m_cursor == L'\r') {
       ++m_cursor;
       return;