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fix Issue 20150 - -dip1000 defeated by pure #12010

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Merged
dlang-bot merged 1 commit into from
Aug 18, 2021
Merged

fix Issue 20150 - -dip1000 defeated by pure #12010

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15 changes: 13 additions & 2 deletions src/dmd/mtype.d
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Original file line number Diff line number Diff line change
Expand Up @@ -4428,15 +4428,15 @@ extern (C++) final class TypeFunction : TypeNext
}
}

stc |= STC.scope_;

/* Inferring STC.return_ here has false positives
* for pure functions, producing spurious error messages
* about escaping references.
* Give up on it for now.
*/
version (none)
{
stc |= STC.scope_;

Type tret = nextOf().toBasetype();
if (isref || tret.hasPointers())
{
Expand All @@ -4446,6 +4446,17 @@ extern (C++) final class TypeFunction : TypeNext
stc |= STC.return_;
}
}
else
{
// Check escaping through return value
Type tret = nextOf().toBasetype();
if (isref || tret.hasPointers())
{
return stc;
}

stc |= STC.scope_;
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@dkorpel dkorpel Jun 1, 2021

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I just realized there should also be a check that the function is nothrow, or else parameters could escape using Exceptions.

import std.stdio;

void escape(string x) @safe pure {
    throw new Exception(x);
}

void main() @safe {
    static string global;
    immutable(char)[4] local;
    try {
        escape(local[]); 
    } catch(Exception e) {
        global = e.msg;
    }
    assert(&local[0] != &global[0]); // fails
}

Though that might be better to do in a follow-up PR, so we can get the fix for the more common case in quicker.

}

return stc;
}
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33 changes: 33 additions & 0 deletions test/fail_compilation/retscope6.d
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Original file line number Diff line number Diff line change
Expand Up @@ -198,3 +198,36 @@ void hmac(scope ubyte[] secret)
ubyte[10] buffer;
secret = buffer[];
}

/* TEST_OUTPUT:
---
fail_compilation/retscope6.d(12011): Error: reference to local variable `x` assigned to non-scope parameter `r` calling retscope6.escape_m_20150
fail_compilation/retscope6.d(12022): Error: reference to local variable `x` assigned to non-scope parameter `r` calling retscope6.escape_c_20150
---
*/

#line 12000

// https://issues.dlang.org/show_bug.cgi?id=20150

int* escape_m_20150(int* r) @safe pure
{
return r;
}

int* f_m_20150() @safe
{
int x = 42;
return escape_m_20150(&x);
}

const(int)* escape_c_20150(const int* r) @safe pure
{
return r;
}

const(int)* f_c_20150() @safe
{
int x = 42;
return escape_c_20150(&x);
}