checks: add unbraced-expr check

docs/violations.md

@@ -12,6 +12,7 @@ This page lists all lint violations that may be reported by `tclint`.
 - [`backslash-spacing`](#backslash-spacing)
 - [`expr-format`](#expr-format)
 - [`spaces-in-braces`](#spaces-in-braces)
+- [`unbraced-expr`](#unbraced-expr)
 
 Each of these violations is sorted into one of two coarse categories, which can
 be displayed using the `--show-categories` CLI option.
@@ -134,3 +135,16 @@ for {set i 0} {$i < 10} {incr i} {
 ### Rationale
 
 Consistent formatting enhances readability.
+
+## `unbraced-expr`
+
+Expressions that contain substitutions should be enclosed by braces.
+
+### Rationale
+
+Without braces, the Tcl parser will perform substitutions before interpreting
+the expression. This is not actually the desired behavior in most cases, and may
+impact functionality in some edge cases. In addition, this can reduce
+performance.
+
+See "Performance Considerations" in the [Tcl docs for `expr`](https://www.tcl.tk/man/tcl/TclCmd/expr.html).

src/tclint/checks.py

@@ -3,7 +3,7 @@
 from tclint.commands import get_commands
 from tclint.violations import Rule, Violation
 
-from tclint.syntax_tree import Visitor, Script, List, ParenExpression
+from tclint.syntax_tree import Visitor, Script, List, ParenExpression, BracedExpression
 
 
 class IndentLevelChecker(Visitor):
@@ -728,6 +728,31 @@ def _check_braced_arg(self, node):
             )
 
 
+class UnbracedExprChecker(Visitor):
+    def check(self, _, tree, __):
+        self._violations = []
+        tree.accept(self, recurse=True)
+        return self._violations
+
+    def visit_command(self, command):
+        if command.routine != "expr":
+            return
+
+        if len(command.args) == 1 and isinstance(command.args[0], BracedExpression):
+            return
+
+        for child in command.args:
+            if child.contents is None:
+                self._violations.append(
+                    Violation(
+                        Rule.UNBRACED_EXPR,
+                        "expression with substitutions should be enclosed by braces",
+                        command.args[0].pos,
+                    )
+                )
+                return
+
+
 def get_checkers():
     return (
         IndentLevelChecker(),
@@ -737,4 +762,5 @@ def get_checkers():
         BlankLineChecker(),
         BackslashNewlineChecker(),
         SpacesInBracesChecker(),
+        UnbracedExprChecker(),
     )

src/tclint/violations.py

@@ -20,6 +20,7 @@ class Rule(Enum):
     BACKSLASH_SPACING = "backslash-spacing"
     EXPR_FORMAT = "expr-format"
     SPACES_IN_BRACES = "spaces-in-braces"
+    UNBRACED_EXPR = "unbraced-expr"
 
     def __str__(self):
         return self.value
@@ -47,6 +48,7 @@ def __str__(self):
     Rule.SPACES_IN_BRACES: Category.STYLE,
     Rule.REDEFINED_BUILTIN: Category.FUNC,
     Rule.COMMAND_ARGS: Category.FUNC,
+    Rule.UNBRACED_EXPR: Category.FUNC,
 }
 
 

tests/data/dirty.tcl

@@ -1,7 +1,7 @@
 for {set i 1}  {$i < 100} {incr i} {
-if {[expr $i % 15] == 0} {
+if {$i % 15 == 0} {
 puts "FizzBuzz"
-}   elseif {[expr $i % 3] == 0} {
+}   elseif {$i % 3 == 0} {
         puts "Fizz"
 } elseif {[expr $i % 5] == 0} {
         puts   "Buzz"

tests/data/dirty.txt

@@ -4,5 +4,6 @@ data/dirty.tcl:3:1: expected indent of 8 spaces, got 0 [indent]
 data/dirty.tcl:4:1: expected indent of 4 spaces, got 0 [indent]
 data/dirty.tcl:4:2: expected 1 space between words, got 3 [spacing]
 data/dirty.tcl:6:1: expected indent of 4 spaces, got 0 [indent]
+data/dirty.tcl:6:17: expression with substitutions should be enclosed by braces [unbraced-expr]
 data/dirty.tcl:7:13: expected 1 space between words, got 3 [spacing]
 data/dirty.tcl:9:13: expected 1 space between words, got 5 [spacing]

tests/test_tclint.py

@@ -84,13 +84,14 @@ def test_switches():
 data/dirty.tcl:4:2: expected 1 space between words, got 3 [spacing]
 data/dirty.tcl:5:1: expected indent of 4 spaces, got 8 [indent]
 data/dirty.tcl:6:1: expected indent of 2 spaces, got 0 [indent]
+data/dirty.tcl:6:17: expression with substitutions should be enclosed by braces [unbraced-expr]
 data/dirty.tcl:7:1: expected indent of 4 spaces, got 8 [indent]
 data/dirty.tcl:7:13: expected 1 space between words, got 3 [spacing]
 data/dirty.tcl:8:1: expected indent of 2 spaces, got 4 [indent]
 data/dirty.tcl:9:1: expected indent of 4 spaces, got 8 [indent]
 data/dirty.tcl:9:13: expected 1 space between words, got 5 [spacing]
 data/dirty.tcl:10:1: expected indent of 2 spaces, got 4 [indent]
-""".lstrip()
+""".lstrip()  # noqa E501
 
     assert p.stdout.decode("utf-8") == expected
     assert p.returncode == 1