templater: provide arithmetic operations on integers

The termwidth template keyword is of limited use without some way to ensure
that margins are respected.

Provide a full set of arithmetic operators (four basic operations plus the
mod function, defined to match Python's // for division), so that you can
create termwidth based layouts that match the user's terminal size

mercurial/help/templates.txt

@@ -43,6 +43,15 b' In addition to filters, there are some b'
 
 .. functionsmarker
 
+We provide a limited set of infix arithmetic operations on integers::
+
+  + for addition
+  - for subtraction
+  * for multiplication
+  / for floor division (division rounded to integer nearest -infinity)
+
+Division fulfils the law x = x / y + mod(x, y).
+
 Also, for any expression that returns a list, there is a list operator::
 
     expr % "{template}"

mercurial/templater.py

@@ -33,6 +33,10 b' elements = {'
     "|": (5, None, None, ("|", 5), None),
     "%": (6, None, None, ("%", 6), None),
     ")": (0, None, None, None, None),
+    "+": (3, None, None, ("+", 3), None),
+    "-": (3, None, ("negate", 10), ("-", 3), None),
+    "*": (4, None, None, ("*", 4), None),
+    "/": (4, None, None, ("/", 4), None),
     "integer": (0, "integer", None, None, None),
     "symbol": (0, "symbol", None, None, None),
     "string": (0, "string", None, None, None),
@@ -48,7 +52,7 b' def tokenize(program, start, end, term=N'
         c = program[pos]
         if c.isspace(): # skip inter-token whitespace
             pass
-        elif c in "(,)%|": # handle simple operators
+        elif c in "(,)%|+-*/": # handle simple operators
             yield (c, None, pos)
         elif c in '"\'': # handle quoted templates
             s = pos + 1
@@ -70,13 +74,8 b' def tokenize(program, start, end, term=N'
                 pos += 1
             else:
                 raise error.ParseError(_("unterminated string"), s)
-        elif c.isdigit() or c == '-':
+        elif c.isdigit():
             s = pos
-            if c == '-': # simply take negate operator as part of integer
-                pos += 1
-            if pos >= end or not program[pos].isdigit():
-                raise error.ParseError(_("integer literal without digits"), s)
-            pos += 1
             while pos < end:
                 d = program[pos]
                 if not d.isdigit():
@@ -420,6 +419,28 b' def runmap(context, mapping, data):'
             # If so, return the expanded value.
             yield i
 
+def buildnegate(exp, context):
+    arg = compileexp(exp[1], context, exprmethods)
+    return (runnegate, arg)
+
+def runnegate(context, mapping, data):
+    data = evalinteger(context, mapping, data,
+                       _('negation needs an integer argument'))
+    return -data
+
+def buildarithmetic(exp, context, func):
+    left = compileexp(exp[1], context, exprmethods)
+    right = compileexp(exp[2], context, exprmethods)
+    return (runarithmetic, (func, left, right))
+
+def runarithmetic(context, mapping, data):
+    func, left, right = data
+    left = evalinteger(context, mapping, left,
+                       _('arithmetic only defined on integers'))
+    right = evalinteger(context, mapping, right,
+                        _('arithmetic only defined on integers'))
+    return func(left, right)
+
 def buildfunc(exp, context):
     n = getsymbol(exp[1])
     args = [compileexp(x, context, exprmethods) for x in getlist(exp[2])]
@@ -713,6 +734,20 b' def localdate(context, mapping, args):'
         tzoffset = util.makedate()[1]
     return (date[0], tzoffset)
 
+@templatefunc('mod(a, b)')
+def mod(context, mapping, args):
+    """Calculate a mod b such that a / b + a mod b == a"""
+    if not len(args) == 2:
+        # i18n: "mod" is a keyword
+        raise error.ParseError(_("mod expects two arguments"))
+
+    left = evalinteger(context, mapping, args[0],
+                       _('arithmetic only defined on integers'))
+    right = evalinteger(context, mapping, args[1],
+                        _('arithmetic only defined on integers'))
+
+    return left % right
+
 @templatefunc('relpath(path)')
 def relpath(context, mapping, args):
     """Convert a repository-absolute path into a filesystem path relative to
@@ -926,6 +961,11 b' exprmethods = {'
     "|": buildfilter,
     "%": buildmap,
     "func": buildfunc,
+    "+": lambda e, c: buildarithmetic(e, c, lambda a, b: a + b),
+    "-": lambda e, c: buildarithmetic(e, c, lambda a, b: a - b),
+    "negate": buildnegate,
+    "*": lambda e, c: buildarithmetic(e, c, lambda a, b: a * b),
+    "/": lambda e, c: buildarithmetic(e, c, lambda a, b: a // b),
     }
 
 # methods to interpret top-level template (e.g. {x}, {x|_}, {x % "y"})

tests/test-command-template.t

@@ -29,6 +29,111 b''
   $ hg merge -q foo
   $ hg commit -m 'merge' -d '1500001 0' -u 'person'
 
+Test arithmetic operators have the right precedence:
+
+  $ hg log -l 1 -T '{date(date, "%s") + 5 * 10} {date(date, "%s") - 2 * 3}\n'
+  1500051 1499995
+  $ hg log -l 1 -T '{date(date, "%s") * 5 + 10} {date(date, "%s") * 3 - 2}\n'
+  7500015 4500001
+
+Test division:
+
+  $ hg debugtemplate -r0 -v '{5 / 2} {mod(5, 2)}\n'
+  (template
+    (/
+      ('integer', '5')
+      ('integer', '2'))
+    ('string', ' ')
+    (func
+      ('symbol', 'mod')
+      (list
+        ('integer', '5')
+        ('integer', '2')))
+    ('string', '\n'))
+  2 1
+  $ hg debugtemplate -r0 -v '{5 / -2} {mod(5, -2)}\n'
+  (template
+    (/
+      ('integer', '5')
+      (negate
+        ('integer', '2')))
+    ('string', ' ')
+    (func
+      ('symbol', 'mod')
+      (list
+        ('integer', '5')
+        (negate
+          ('integer', '2'))))
+    ('string', '\n'))
+  -3 -1
+  $ hg debugtemplate -r0 -v '{-5 / 2} {mod(-5, 2)}\n'
+  (template
+    (/
+      (negate
+        ('integer', '5'))
+      ('integer', '2'))
+    ('string', ' ')
+    (func
+      ('symbol', 'mod')
+      (list
+        (negate
+          ('integer', '5'))
+        ('integer', '2')))
+    ('string', '\n'))
+  -3 1
+  $ hg debugtemplate -r0 -v '{-5 / -2} {mod(-5, -2)}\n'
+  (template
+    (/
+      (negate
+        ('integer', '5'))
+      (negate
+        ('integer', '2')))
+    ('string', ' ')
+    (func
+      ('symbol', 'mod')
+      (list
+        (negate
+          ('integer', '5'))
+        (negate
+          ('integer', '2'))))
+    ('string', '\n'))
+  2 -1
+
+Filters bind closer than arithmetic:
+
+  $ hg debugtemplate -r0 -v '{revset(".")|count - 1}\n'
+  (template
+    (-
+      (|
+        (func
+          ('symbol', 'revset')
+          ('string', '.'))
+        ('symbol', 'count'))
+      ('integer', '1'))
+    ('string', '\n'))
+  0
+
+But negate binds closer still:
+
+  $ hg debugtemplate -r0 -v '{1-3|stringify}\n'
+  (template
+    (-
+      ('integer', '1')
+      (|
+        ('integer', '3')
+        ('symbol', 'stringify')))
+    ('string', '\n'))
+  hg: parse error: arithmetic only defined on integers
+  [255]
+  $ hg debugtemplate -r0 -v '{-3|stringify}\n'
+  (template
+    (|
+      (negate
+        ('integer', '3'))
+      ('symbol', 'stringify'))
+    ('string', '\n'))
+  -3
+
 Second branch starting at nullrev:
 
   $ hg update null
@@ -2890,14 +2995,15 b' Test integer literal:'
   $ hg debugtemplate -v '{(-4)}\n'
   (template
     (group
-      ('integer', '-4'))
+      (negate
+        ('integer', '4')))
     ('string', '\n'))
   -4
   $ hg debugtemplate '{(-)}\n'
-  hg: parse error at 2: integer literal without digits
+  hg: parse error at 3: not a prefix: )
   [255]
   $ hg debugtemplate '{(-a)}\n'
-  hg: parse error at 2: integer literal without digits
+  hg: parse error: negation needs an integer argument
   [255]
 
 top-level integer literal is interpreted as symbol (i.e. variable name):