https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106549
Bug ID: 106549
Summary: excessive error messages with nested undefined
template
Product: gcc
Version: 10.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: f.heckenb...@fh-soft.de
Target Milestone: ---
% cat test.cpp
void f (X <X <X <X <X <X <X <int>>>>>>>);
% g++ --std=c++20 test.cpp |& head -n 30
test.cpp:1:27: error: 'X' was not declared in this scope
1 | void f (X <X <X <X <X <X <X <int>>>>>>>);
| ^
test.cpp:1:27: error: 'X' was not declared in this scope
test.cpp:1:27: error: 'X' was not declared in this scope
test.cpp:1:27: error: 'X' was not declared in this scope
test.cpp:1:27: error: 'X' was not declared in this scope
test.cpp:1:27: error: 'X' was not declared in this scope
test.cpp:1:27: error: 'X' was not declared in this scope
test.cpp:1:27: error: 'X' was not declared in this scope
test.cpp:1:27: error: 'X' was not declared in this scope
test.cpp:1:27: error: 'X' was not declared in this scope
test.cpp:1:27: error: 'X' was not declared in this scope
test.cpp:1:24: error: 'X' was not declared in this scope
1 | void f (X <X <X <X <X <X <X <int>>>>>>>);
| ^
test.cpp:1:27: error: 'X' was not declared in this scope
1 | void f (X <X <X <X <X <X <X <int>>>>>>>);
| ^
test.cpp:1:27: error: 'X' was not declared in this scope
test.cpp:1:27: error: 'X' was not declared in this scope
test.cpp:1:27: error: 'X' was not declared in this scope
test.cpp:1:27: error: 'X' was not declared in this scope
test.cpp:1:27: error: 'X' was not declared in this scope
test.cpp:1:27: error: 'X' was not declared in this scope
test.cpp:1:27: error: 'X' was not declared in this scope
test.cpp:1:27: error: 'X' was not declared in this scope
test.cpp:1:27: error: 'X' was not declared in this scope
test.cpp:1:27: error: 'X' was not declared in this scope
test.cpp:1:27: error: 'X' was not declared in this scope
% g++ --std=c++20 test.cpp |& wc
2921195 24780807 155318228
I don't have newer GCC versions installed locally, but according to a Godbolt
test, it seems to happen with them too (but since Godbolt truncates the
messages, I can't tell whether they produce quite the same amount).
The number of messages seems to grow exponentially with the number of template
nestings with a growth factor >11.
PS: Couldn't resist the opportunity to turn compiler output into an
animation/screensaver: ;)
g++ --std=c++20 test.cpp |& sed -un 's/ / /g;s/^ | //p' | tr -d '\n'
