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turn mutable case variables into an error

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dkorpel 2021-07-09 16:19:33 +02:00 • committed by Nicholas Wilson
parent 03c87db6ed
commit 645e94fb84
6 changed files with 34 additions and 25 deletions
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16
changelog/mutable-cases.dd Normal file
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@ -0,0 +1,16 @@
Using a mutable variable as a switch case now triggers an error
Variables that are `const` or `immutable` can be used as switch cases even if they are initialized at run-time, but using variables that are mutable has been deprecated since dmd 2.073.2.
This deprecation has now been turned into an error:
-------
void foo(int s, int x, const int y, immutable int z) {
switch (s) {
case x: // error
case y: // allowed
case z: // allowed
default:
}
}
-------
It is advised to only use compile-time known values in `case` statements, because the presence of any run-time variable (even a `const` or `immutable` one) results in the entire switch being lowered to a series of if-else statements before code generation, instead of an efficient jump table.
Prefer regular if-statements for comparing pairs of run-time known variables.

2
src/dmd/statementsem.d
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@ -2913,7 +2913,7 @@ private extern (C++) final class StatementSemanticVisitor : Visitor
*/
if (!v.isConst() && !v.isImmutable())
{
cs.deprecation("`case` variables have to be `const` or `immutable`");
cs.error("`case` variables have to be `const` or `immutable`");
}
if (sw.isFinal)

11
test/compilable/b17111.d
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@ -1,16 +1,7 @@
/*
TEST_OUTPUT:
---
compilable/b17111.d(16): Deprecation: `case` variables have to be `const` or `immutable`
compilable/b17111.d(17): Deprecation: `case` variables have to be `const` or `immutable`
---
*/
alias TestType = ubyte;
void test()
void test(immutable TestType a, immutable TestType b, TestType c)
{
TestType a,b,c;
switch(c)
{
case a: break;

11
test/compilable/interpret3.d
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@ -2,8 +2,7 @@
/*
TEST_OUTPUT:
---
compilable/interpret3.d(2914): Deprecation: `case` variables have to be `const` or `immutable`
compilable/interpret3.d(6351): Deprecation: identity comparison of static arrays implicitly coerces them to slices, which are compared by reference
compilable/interpret3.d(6350): Deprecation: identity comparison of static arrays implicitly coerces them to slices, which are compared by reference
---
*/
@ -2904,16 +2903,16 @@ static assert(bug4448b() == 3);
/**************************************************/
// https://issues.dlang.org/show_bug.cgi?id=6985
// non-constant case
// Formerly, non-constant case, but switch cases with mutable cases now error
// Currently: run-time constant variable case
int bug6985(int z)
{
int q = z * 2 - 6;
const int q = z * 2 - 6;
switch(z)
{
case q:
q = 87;
break;
return 87;
default:
}
return q;

16
test/fail_compilation/ice17831.d
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@ -1,12 +1,16 @@
// REQUIRED_ARGS: -d
/*
TEST_OUTPUT:
---
fail_compilation/ice17831.d(19): Error: `case` variable `i` declared at fail_compilation/ice17831.d(17) cannot be declared in `switch` body
fail_compilation/ice17831.d(33): Error: `case` variable `i` declared at fail_compilation/ice17831.d(31) cannot be declared in `switch` body
fail_compilation/ice17831.d(48): Error: `case` variable `i` declared at fail_compilation/ice17831.d(45) cannot be declared in `switch` body
fail_compilation/ice17831.d(61): Error: `case` variable `i` declared at fail_compilation/ice17831.d(60) cannot be declared in `switch` body
fail_compilation/ice17831.d(73): Error: `case` variable `i` declared at fail_compilation/ice17831.d(72) cannot be declared in `switch` body
fail_compilation/ice17831.d(23): Error: `case` variables have to be `const` or `immutable`
fail_compilation/ice17831.d(23): Error: `case` variable `i` declared at fail_compilation/ice17831.d(21) cannot be declared in `switch` body
fail_compilation/ice17831.d(37): Error: `case` variables have to be `const` or `immutable`
fail_compilation/ice17831.d(37): Error: `case` variable `i` declared at fail_compilation/ice17831.d(35) cannot be declared in `switch` body
fail_compilation/ice17831.d(52): Error: `case` variables have to be `const` or `immutable`
fail_compilation/ice17831.d(52): Error: `case` variable `i` declared at fail_compilation/ice17831.d(49) cannot be declared in `switch` body
fail_compilation/ice17831.d(65): Error: `case` variables have to be `const` or `immutable`
fail_compilation/ice17831.d(65): Error: `case` variable `i` declared at fail_compilation/ice17831.d(64) cannot be declared in `switch` body
fail_compilation/ice17831.d(77): Error: `case` variables have to be `const` or `immutable`
fail_compilation/ice17831.d(77): Error: `case` variable `i` declared at fail_compilation/ice17831.d(76) cannot be declared in `switch` body
---
*/

3
test/fail_compilation/test16523.d
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@ -1,8 +1,7 @@
// REQUIRED_ARGS: -de
/*
TEST_OUTPUT:
---
fail_compilation/test16523.d(13): Deprecation: `case` variables have to be `const` or `immutable`
fail_compilation/test16523.d(12): Error: `case` variables have to be `const` or `immutable`
---
*/