lintr does not like for loop bodies with a single line and no braces

[rlaboiss]

R accepts single-line bodies, without curly braces, for theif and the for statements.

Is there any reason why lintr accepts that for if but not for for? For instance:

> lint("if (TRUE)\n  x")
> lint("for (i in 0)\n  x")
<text>:2:2: style: [indentation_linter] Indentation should be 0 spaces but is 2 spaces.

[IndrajeetPatil]

There is definitely an inconsistency here. Thanks for pointing out.

cat("if (TRUE)\n  x")
#> if (TRUE)
#>   x
cat("for (i in 0)\n  x")
#> for (i in 0)
#>   x
cat("while (TRUE)\n  x")
#> while (TRUE)
#>   x

lintr::lint(text= "if (TRUE)\n  x", linters = lintr::indentation_linter())
lintr::lint(text= "for (i in 0)\n  x", linters = lintr::indentation_linter())
#> <text>:2:2: style: [indentation_linter] Indentation should be 0 spaces but is 2 spaces.
#>   x
#> ~^
lintr::lint(text= "while (TRUE)\n  x", linters = lintr::indentation_linter())

^{Created on 2024-04-23 with reprex v2.1.0}

[MichaelChirico]

Just came across this myself:

lint(linters=indentation_linter(), "
for (i in 1:10)
  i
")
# <text>:3:2: style: [indentation_linter] Indentation should be 0 spaces but is 2 spaces.
#   i
# ~^

https://github.com/r-lib/bit64/blob/81b51fa68622e90dfa15d527bc6591adb499164c/tests/testthat/test-bit64-package.R#L59-L60

[MichaelChirico]

I think the key is that for loops show up differently on the AST than the other control loops, c.f.

str2xml = \(s) writeLines(xmlparsedata::xml_parse_data(parse(text = s), pretty=TRUE))
str2xml("
if (a > 1) 1
while (a > 1) 1
function(x) 1
for (a in 1:10) 1
")

<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
<exprlist>
  <expr line1="2" col1="1" line2="2" col2="12" start="37" end="48">
    <IF line1="2" col1="1" line2="2" col2="2" start="37" end="38">if</IF>
    <OP-LEFT-PAREN line1="2" col1="4" line2="2" col2="4" start="40" end="40">(</OP-LEFT-PAREN>
    <expr line1="2" col1="5" line2="2" col2="9" start="41" end="45">
      <expr line1="2" col1="5" line2="2" col2="5" start="41" end="41">
        <SYMBOL line1="2" col1="5" line2="2" col2="5" start="41" end="41">a</SYMBOL>
      </expr>
      <GT line1="2" col1="7" line2="2" col2="7" start="43" end="43">&gt;</GT>
      <expr line1="2" col1="9" line2="2" col2="9" start="45" end="45">
        <NUM_CONST line1="2" col1="9" line2="2" col2="9" start="45" end="45">1</NUM_CONST>
      </expr>
    </expr>
    <OP-RIGHT-PAREN line1="2" col1="10" line2="2" col2="10" start="46" end="46">)</OP-RIGHT-PAREN>
    <expr line1="2" col1="12" line2="2" col2="12" start="48" end="48">
      <NUM_CONST line1="2" col1="12" line2="2" col2="12" start="48" end="48">1</NUM_CONST>
    </expr>
  </expr>
  <expr line1="3" col1="1" line2="3" col2="15" start="55" end="69">
    <WHILE line1="3" col1="1" line2="3" col2="5" start="55" end="59">while</WHILE>
    <OP-LEFT-PAREN line1="3" col1="7" line2="3" col2="7" start="61" end="61">(</OP-LEFT-PAREN>
    <expr line1="3" col1="8" line2="3" col2="12" start="62" end="66">
      <expr line1="3" col1="8" line2="3" col2="8" start="62" end="62">
        <SYMBOL line1="3" col1="8" line2="3" col2="8" start="62" end="62">a</SYMBOL>
      </expr>
      <GT line1="3" col1="10" line2="3" col2="10" start="64" end="64">&gt;</GT>
      <expr line1="3" col1="12" line2="3" col2="12" start="66" end="66">
        <NUM_CONST line1="3" col1="12" line2="3" col2="12" start="66" end="66">1</NUM_CONST>
      </expr>
    </expr>
    <OP-RIGHT-PAREN line1="3" col1="13" line2="3" col2="13" start="67" end="67">)</OP-RIGHT-PAREN>
    <expr line1="3" col1="15" line2="3" col2="15" start="69" end="69">
      <NUM_CONST line1="3" col1="15" line2="3" col2="15" start="69" end="69">1</NUM_CONST>
    </expr>
  </expr>
  <expr line1="4" col1="1" line2="4" col2="13" start="73" end="85">
    <FUNCTION line1="4" col1="1" line2="4" col2="8" start="73" end="80">function</FUNCTION>
    <OP-LEFT-PAREN line1="4" col1="9" line2="4" col2="9" start="81" end="81">(</OP-LEFT-PAREN>
    <SYMBOL_FORMALS line1="4" col1="10" line2="4" col2="10" start="82" end="82">x</SYMBOL_FORMALS>
    <OP-RIGHT-PAREN line1="4" col1="11" line2="4" col2="11" start="83" end="83">)</OP-RIGHT-PAREN>
    <expr line1="4" col1="13" line2="4" col2="13" start="85" end="85">
      <NUM_CONST line1="4" col1="13" line2="4" col2="13" start="85" end="85">1</NUM_CONST>
    </expr>
  </expr>
  <expr line1="4" col1="1" line2="4" col2="17" start="73" end="89">
    <FOR line1="4" col1="1" line2="4" col2="3" start="73" end="75">for</FOR>
    <forcond line1="4" col1="5" line2="4" col2="15" start="77" end="87">
      <OP-LEFT-PAREN line1="4" col1="5" line2="4" col2="5" start="77" end="77">(</OP-LEFT-PAREN>
      <SYMBOL line1="4" col1="6" line2="4" col2="6" start="78" end="78">a</SYMBOL>
      <IN line1="4" col1="8" line2="4" col2="9" start="80" end="81">in</IN>
      <expr line1="4" col1="11" line2="4" col2="14" start="83" end="86">
        <expr line1="4" col1="11" line2="4" col2="11" start="83" end="83">
          <NUM_CONST line1="4" col1="11" line2="4" col2="11" start="83" end="83">1</NUM_CONST>
        </expr>
        <OP-COLON line1="4" col1="12" line2="4" col2="12" start="84" end="84">:</OP-COLON>
        <expr line1="4" col1="13" line2="4" col2="14" start="85" end="86">
          <NUM_CONST line1="4" col1="13" line2="4" col2="14" start="85" end="86">10</NUM_CONST>
        </expr>
      </expr>
      <OP-RIGHT-PAREN line1="4" col1="15" line2="4" col2="15" start="87" end="87">)</OP-RIGHT-PAREN>
    </forcond>
    <expr line1="4" col1="17" line2="4" col2="17" start="89" end="89">
      <NUM_CONST line1="4" col1="17" line2="4" col2="17" start="89" end="89">1</NUM_CONST>
    </expr>
  </expr>
</exprlist>

Note that path to the left-paren in each case:

• if : //IF/following-sibling::OP-LEFT-PAREN
• while: //WHILE/following-sibling::OP-LEFT-PAREN
• function: //FUNCTION/following-sibling::OP-LEFT-PAREN
• for: //FOR/following-sibling::forcond/OP-LEFT-PAREN