Normalize floats

build/rewrite.go

@@ -137,6 +137,7 @@ var rewrites = []struct {
 	{"formatdocstrings", formatDocstrings, scopeBoth},
 	{"reorderarguments", reorderArguments, scopeBoth},
 	{"editoctal", editOctals, scopeBoth},
+	{"editfloat", editFloats, scopeBoth},
 }
 
 // leaveAlone reports whether any of the nodes on the stack are marked
@@ -1399,6 +1400,35 @@ func editOctals(f *File, _ *Rewriter) {
 	})
 }
 
+// editFloats inserts '0' before the decimal point in floats and normalizes the
+// exponent part to lowercase, no plus sign, and no leading zero.
+func editFloats(f *File, _ *Rewriter) {
+	Walk(f, func(expr Expr, stack []Expr) {
+		l, ok := expr.(*LiteralExpr)
+		if !ok {
+			return
+		}
+		if !strings.ContainsRune(l.Token, '.') {
+			return
+		}
+		if strings.HasPrefix(l.Token, ".") {
+			l.Token = "0" + l.Token
+		}
+		if !strings.ContainsAny(l.Token, "eE") {
+			return
+		}
+		parts := strings.SplitN(l.Token, "e", 2)
+		if len(parts) != 2 {
+			parts = strings.SplitN(l.Token, "E", 2)
+		}
+		if len(parts) != 2 {
+			// Invalid float, skip rewriting.
+			return
+		}
+		l.Token = parts[0] + "e" + strings.TrimLeft(parts[1], "0+")
+	})
+}
+
 // removeParens removes trivial parens
 func removeParens(f *File, _ *Rewriter) {
 	var simplify func(expr Expr, stack []Expr) Expr

build/testdata/003.golden

@@ -3,7 +3,7 @@ numbers = [
     11,
     123.456,
     123.,
-    .456,
+    0.456,
     1.23e45,
     -1,
     +1,
@@ -15,7 +15,12 @@ numbers = [
     1e6,
     -1e6,
     -1.23e-45,
-    3.539537889086625e+24,
-    3.539537889086625E+24,
+    3.539537889086625e24,
+    3.539537889086625e24,
+    3.539537889086625e24000,
+    3.539537889086625e24000,
     3539537889086624823140625,
+    0x123,
+    0xE45,
+    0xe45,
 ]

build/testdata/003.in

@@ -17,5 +17,10 @@ numbers = [
   -1.23e-45,
   3.539537889086625e+24,
   3.539537889086625E+24,
+  3.539537889086625e00024000,
+  3.539537889086625e+00024000,
   3539537889086624823140625,
+  0x123,
+  0xE45,
+  0xe45,
 ]