[clang][Parse] Diagnose useless null statements / empty init-statements
Summary:
clang has `-Wextra-semi` (D43162), which is not dictated by the currently selected standard.
While that is great, there is at least one more source of need-less semis - 'null statements'.
Sometimes, they are needed:
```
for(int x = 0; continueToDoWork(x); x++)
; // Ugly code, but the semi is needed here.
```
But sometimes they are just there for no reason:
```
switch(X) {
case 0:
return -2345;
case 5:
return 0;
default:
return 42;
}; // <- oops
;;;;;;;;;;; <- OOOOPS, still not diagnosed. Clearly this is junk.
```
Additionally:
```
if(; // <- empty init-statement
true)
;
switch (; // empty init-statement
x) {
...
}
for (; // <- empty init-statement
int y : S())
;
}
As usual, things may or may not go sideways in the presence of macros.
While evaluating this diag on my codebase of interest, it was unsurprisingly
discovered that Google Test macros are *very* prone to this.
And it seems many issues are deep within the GTest itself, not
in the snippets passed from the codebase that uses GTest.
So after some thought, i decided not do issue a diagnostic if the semi
is within *any* macro, be it either from the normal header, or system header.
Fixes [[ https://bugs.llvm.org/show_bug.cgi?id=39111 | PR39111 ]]
Reviewers: rsmith, aaron.ballman, efriedma
Reviewed By: aaron.ballman
Subscribers: cfe-commits
Differential Revision: https://reviews.llvm.org/D52695
llvm-svn: 347339
diff --git a/clang/lib/Parse/ParseStmt.cpp b/clang/lib/Parse/ParseStmt.cpp
index 8461ee1..992997e 100644
--- a/clang/lib/Parse/ParseStmt.cpp
+++ b/clang/lib/Parse/ParseStmt.cpp
@@ -930,6 +930,34 @@
}
+/// Consume any extra semi-colons resulting in null statements,
+/// returning true if any tok::semi were consumed.
+bool Parser::ConsumeNullStmt(StmtVector &Stmts) {
+ if (!Tok.is(tok::semi))
+ return false;
+
+ SourceLocation StartLoc = Tok.getLocation();
+ SourceLocation EndLoc;
+
+ while (Tok.is(tok::semi) && !Tok.hasLeadingEmptyMacro() &&
+ Tok.getLocation().isValid() && !Tok.getLocation().isMacroID()) {
+ EndLoc = Tok.getLocation();
+
+ // Don't just ConsumeToken() this tok::semi, do store it in AST.
+ StmtResult R = ParseStatementOrDeclaration(Stmts, ACK_Any);
+ if (R.isUsable())
+ Stmts.push_back(R.get());
+ }
+
+ // Did not consume any extra semi.
+ if (EndLoc.isInvalid())
+ return false;
+
+ Diag(StartLoc, diag::warn_null_statement)
+ << FixItHint::CreateRemoval(SourceRange(StartLoc, EndLoc));
+ return true;
+}
+
/// ParseCompoundStatementBody - Parse a sequence of statements and invoke the
/// ActOnCompoundStmt action. This expects the '{' to be the current token, and
/// consume the '}' at the end of the block. It does not manipulate the scope
@@ -992,6 +1020,9 @@
continue;
}
+ if (ConsumeNullStmt(Stmts))
+ continue;
+
StmtResult R;
if (Tok.isNot(tok::kw___extension__)) {
R = ParseStatementOrDeclaration(Stmts, ACK_Any);
@@ -1588,10 +1619,15 @@
ParsedAttributesWithRange attrs(AttrFactory);
MaybeParseCXX11Attributes(attrs);
+ SourceLocation EmptyInitStmtSemiLoc;
+
// Parse the first part of the for specifier.
if (Tok.is(tok::semi)) { // for (;
ProhibitAttributes(attrs);
// no first part, eat the ';'.
+ SourceLocation SemiLoc = Tok.getLocation();
+ if (!Tok.hasLeadingEmptyMacro() && !SemiLoc.isMacroID())
+ EmptyInitStmtSemiLoc = SemiLoc;
ConsumeToken();
} else if (getLangOpts().CPlusPlus && Tok.is(tok::identifier) &&
isForRangeIdentifier()) {
@@ -1723,6 +1759,11 @@
: diag::ext_for_range_init_stmt)
<< (FirstPart.get() ? FirstPart.get()->getSourceRange()
: SourceRange());
+ if (EmptyInitStmtSemiLoc.isValid()) {
+ Diag(EmptyInitStmtSemiLoc, diag::warn_empty_init_statement)
+ << /*for-loop*/ 2
+ << FixItHint::CreateRemoval(EmptyInitStmtSemiLoc);
+ }
}
} else {
ExprResult SecondExpr = ParseExpression();