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Commit0d0aa5d

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Provide some static-assertion functionality on all compilers.
On reflection (especially after noticing how many buildfarm critters have__builtin_types_compatible_p but not _Static_assert), it seems like weought to try a bit harder to make these macros do something everywhere.The initial cut at it would have been no help to code that is compiled onlyon platforms without _Static_assert, for instance; and in any case not allour contributors do their initial coding on the latest gcc version.Some googling about static assertions turns up quite a bit of prior artfor making it work in compilers that lack _Static_assert. The methodthat seems closest to our needs involves defining a struct with a bit-fieldthat has negative width if the assertion condition fails. There seems noreliable way to get the error message string to be output, but throwing acompile error with a confusing message is better than missing the problemaltogether.In the same spirit, if we don't have __builtin_types_compatible_p we can atleast insist that the variable have the same width as the type. This won'tcatch errors such as "wrong pointer type", but it's far better thannothing.In addition to changing the macro definitions, adjust acompile-time-constant Assert in contrib/hstore to use StaticAssertStmt,so we can get some buildfarm coverage on whether that macro behaves sanelyor not. There's surely more places that could be converted, but this isthe first one I came across.
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2 files changed

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2 files changed

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‎contrib/hstore/hstore_compat.c

Lines changed: 3 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -94,7 +94,7 @@
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* etc. are compatible.
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*
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* If the above statement isn't true on some bizarre platform, we're
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* a bit hosed (seeAssert in hstoreValidOldFormat).
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* a bit hosed (seeStaticAssertStmt in hstoreValidOldFormat).
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*/
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typedefstruct
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{
@@ -180,7 +180,8 @@ hstoreValidOldFormat(HStore *hs)
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return0;
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/* New format uses an HEntry for key and another for value */
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Assert(sizeof(HOldEntry)== (2*sizeof(HEntry)));
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StaticAssertStmt(sizeof(HOldEntry)==2*sizeof(HEntry),
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"old hstore format is not upward-compatible");
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if (count==0)
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return2;

‎src/include/c.h

Lines changed: 20 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -690,23 +690,29 @@ typedef NameData *Name;
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/*
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* Macros to support compile-time assertion checks, if the compiler has them.
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* Macros to support compile-time assertion checks.
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*
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* If the "condition" (a compile-time-constant expression) evaluates to false,
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* throw a compile error using the "errmessage" (a string literal).
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*
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* gcc 4.6 and up supports _Static_assert(), butit has bizarre syntactic
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* gcc 4.6 and up supports _Static_assert(), butthere are bizarre syntactic
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* placement restrictions. These macros make it safe to use as a statement
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* or in an expression, respectively.
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*
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* Otherwise we fall back on a kluge that assumes the compiler will complain
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* about a negative width for a struct bit-field. This will not include a
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* helpful error message, but it beats not getting an error at all.
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*/
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#ifdefHAVE__STATIC_ASSERT
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#defineStaticAssertStmt(condition,errmessage) \
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do { _Static_assert(condition, errmessage); } while(0)
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#defineStaticAssertExpr(condition,errmessage) \
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({ StaticAssertStmt(condition, errmessage); true; })
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#else/* !HAVE__STATIC_ASSERT */
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#defineStaticAssertStmt(condition,errmessage)
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#defineStaticAssertExpr(condition,errmessage) ((void) true)
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#defineStaticAssertStmt(condition,errmessage) \
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((void) sizeof(struct { int static_assert_failure : (condition) ? 1 : -1; }))
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#defineStaticAssertExpr(condition,errmessage) \
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StaticAssertStmt(condition, errmessage)
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#endif/* HAVE__STATIC_ASSERT */
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@@ -716,6 +722,10 @@ typedef NameData *Name;
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* AssertVariableIsOfType() can be used as a statement.
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* AssertVariableIsOfTypeMacro() is intended for use in macros, eg
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*#define foo(x) (AssertVariableIsOfTypeMacro(x, int), bar(x))
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*
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* If we don't have __builtin_types_compatible_p, we can still assert that
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* the types have the same size. This is far from ideal (especially on 32-bit
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* platforms) but it provides at least some coverage.
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*/
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#ifdefHAVE__BUILTIN_TYPES_COMPATIBLE_P
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#defineAssertVariableIsOfType(varname,typename) \
@@ -725,8 +735,12 @@ typedef NameData *Name;
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StaticAssertExpr(__builtin_types_compatible_p(__typeof__(varname), typename), \
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CppAsString(varname) " does not have type " CppAsString(typename))
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#else/* !HAVE__BUILTIN_TYPES_COMPATIBLE_P */
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#defineAssertVariableIsOfType(varname,typename)
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#defineAssertVariableIsOfTypeMacro(varname,typename) ((void) true)
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#defineAssertVariableIsOfType(varname,typename) \
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StaticAssertStmt(sizeof(varname) == sizeof(typename), \
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CppAsString(varname) " does not have type " CppAsString(typename))
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#defineAssertVariableIsOfTypeMacro(varname,typename) \
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StaticAssertExpr(sizeof(varname) == sizeof(typename), \
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CppAsString(varname) " does not have type " CppAsString(typename))
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#endif/* HAVE__BUILTIN_TYPES_COMPATIBLE_P */
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