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Help: Clarify precedence of AND and OR in 'if' conditions

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The wording update in commit b74819e4fe (Help: Format 'if' command
documentation, 2013-12-18, v3.0.0-rc1~227^2~1) incorrectly implied that
`AND` has higher precedence than `OR`.  Although this is common in many
languages, it has never been true in CMake's implementation.  Revise
the wording to clarify the precedence.

Add a test case demonstrating the order.

Fixes: #23207
This commit is contained in:
Brad King 2022-02-09 14:16:50 -05:00
parent a15cc7706d
commit 41adfc6b04
4 changed files with 24 additions and 8 deletions
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23
Help/command/if.rst
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@ -38,14 +38,21 @@ The following syntax applies to the ``condition`` argument of
the ``if``, ``elseif`` and :command:`while` clauses.
Compound conditions are evaluated in the following order of precedence:
Innermost parentheses are evaluated first. Next come unary tests such
as `EXISTS`_, `COMMAND`_, and `DEFINED`_. Then binary tests such as
`EQUAL`_, `LESS`_, `LESS_EQUAL`_, `GREATER`_, `GREATER_EQUAL`_,
`STREQUAL`_, `STRLESS`_, `STRLESS_EQUAL`_, `STRGREATER`_,
`STRGREATER_EQUAL`_, `VERSION_EQUAL`_, `VERSION_LESS`_,
`VERSION_LESS_EQUAL`_, `VERSION_GREATER`_, `VERSION_GREATER_EQUAL`_,
and `MATCHES`_. Then the boolean operators in the order `NOT`_, `AND`_,
and finally `OR`_.
1. Parentheses.
2. Unary tests such as `EXISTS`_, `COMMAND`_, and `DEFINED`_.
3. Binary tests such as `EQUAL`_, `LESS`_, `LESS_EQUAL`_, `GREATER`_,
`GREATER_EQUAL`_, `STREQUAL`_, `STRLESS`_, `STRLESS_EQUAL`_,
`STRGREATER`_, `STRGREATER_EQUAL`_, `VERSION_EQUAL`_, `VERSION_LESS`_,
`VERSION_LESS_EQUAL`_, `VERSION_GREATER`_, `VERSION_GREATER_EQUAL`_,
and `MATCHES`_.
4. Unary logical operator `NOT`_.
5. Binary logical operators `AND`_ and `OR`_, from left to right,
without any short-circuit.
Basic Expressions
"""""""""""""""""

1
Tests/RunCMake/if/AndOr-stdout.txt Normal file
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@ -0,0 +1 @@
-- OR and AND correctly evaluated left to right

6
Tests/RunCMake/if/AndOr.cmake Normal file
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@ -0,0 +1,6 @@
# AND and OR are the same precedence
if(1 OR 0 AND 0) # equivalent to ((1 OR 0) AND 0)
message(FATAL_ERROR "AND incorrectly evaluated before OR")
else()
message(STATUS "OR and AND correctly evaluated left to right")
endif()

2
Tests/RunCMake/if/RunCMakeTest.cmake
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@ -17,3 +17,5 @@ run_cmake(IncompleteMatchesFail)
run_cmake(TestNameThatExists)
run_cmake(TestNameThatDoesNotExist)
run_cmake_script(AndOr)