[Diagnostic] Add ftabstop to -Wmisleading-indentation

Summary:
this allow much better support of codebases like the linux kernel that mix tabs and spaces.

-ftabstop=//Width// allow specifying how large tabs are considered to be.

Reviewers: xbolva00, aaron.ballman, rsmith

Reviewed By: aaron.ballman

Subscribers: jyknight, riccibruno, rsmith, nathanchance

Differential Revision: https://reviews.llvm.org/D71037

1 files changed, 38 insertions, 3 deletions

diff --git a/clang/lib/Parse/ParseStmt.cpp b/clang/lib/Parse/ParseStmt.cpp
index 203f30610ce..7fc2f2a2b32 100644
--- a/clang/lib/Parse/ParseStmt.cpp
+++ b/clang/lib/Parse/ParseStmt.cpp
@@ -1214,6 +1214,41 @@ struct MisleadingIndentationChecker {
     if (Kind == MSK_else && !ShouldSkip)
       P.MisleadingIndentationElseLoc = SL;
   }
+
+  /// Compute the column number will aligning tabs on TabStop (-ftabstop), this
+  /// gives the visual indentation of the SourceLocation.
+  static unsigned getVisualIndentation(SourceManager &SM, SourceLocation Loc) {
+    unsigned TabStop = SM.getDiagnostics().getDiagnosticOptions().TabStop;
+
+    unsigned ColNo = SM.getSpellingColumnNumber(Loc);
+    if (ColNo == 0 || TabStop == 1)
+      return ColNo;
+
+    std::pair<FileID, unsigned> FIDAndOffset = SM.getDecomposedLoc(Loc);
+
+    bool Invalid;
+    StringRef BufData = SM.getBufferData(FIDAndOffset.first, &Invalid);
+    if (Invalid)
+      return 0;
+
+    const char *EndPos = BufData.data() + FIDAndOffset.second;
+    assert(FIDAndOffset.second > ColNo &&
+           "Column number smaller than file offset?");
+
+    unsigned VisualColumn = 0; // Stored as 0-based column, here.
+    // Loop from beginning of line up to Loc's file position, counting columns,
+    // expanding tabs.
+    for (const char *CurPos = EndPos - (ColNo - 1); CurPos != EndPos;
+         ++CurPos) {
+      if (*CurPos == '\t')
+        // Advance visual column to next tabstop.
+        VisualColumn += (TabStop - VisualColumn % TabStop);
+      else
+        VisualColumn++;
+    }
+    return VisualColumn + 1;
+  }
+
   void Check() {
     Token Tok = P.getCurToken();
     if (P.getActions().getDiagnostics().isIgnored(
@@ -1230,9 +1265,9 @@ struct MisleadingIndentationChecker {
       P.MisleadingIndentationElseLoc = SourceLocation();
 
     SourceManager &SM = P.getPreprocessor().getSourceManager();
-    unsigned PrevColNum = SM.getSpellingColumnNumber(PrevLoc);
-    unsigned CurColNum = SM.getSpellingColumnNumber(Tok.getLocation());
-    unsigned StmtColNum = SM.getSpellingColumnNumber(StmtLoc);
+    unsigned PrevColNum = getVisualIndentation(SM, PrevLoc);
+    unsigned CurColNum = getVisualIndentation(SM, Tok.getLocation());
+    unsigned StmtColNum = getVisualIndentation(SM, StmtLoc);
 
     if (PrevColNum != 0 && CurColNum != 0 && StmtColNum != 0 &&
         ((PrevColNum > StmtColNum && PrevColNum == CurColNum) ||