Fix and improve float formatting (#1309)

* Don't break `12e+34` into `12e + 34`

* Better implementation

* Normalize floats

build/lex.go

@@ -318,12 +318,17 @@ func (in *input) startToken(val *yySymType) {
 // has not done that already.
 func (in *input) endToken(val *yySymType) {
 	if val.tok == "" {
-		tok := string(in.token[:len(in.token)-len(in.remaining)])
+		tok := string(in.peekToken())
 		val.tok = tok
 		in.lastToken = val.tok
 	}
 }
 
+// peekToken returns the bytes comprising the current token being scanned.
+func (in *input) peekToken() []byte {
+	return in.token[:len(in.token)-len(in.remaining)]
+}
+
 // Lex is called from the generated parser to obtain the next input token.
 // It returns the token value (either a rune like '+' or a symbolic token _FOR)
 // and sets val to the data associated with the token.
@@ -619,7 +624,15 @@ func (in *input) Lex(val *yySymType) int {
 	for {
 		c := in.peekRune()
 		if !isIdent(c) {
-			break
+			if c == '+' || c == '-' {
+				t := in.peekToken()
+				// Parse 12.3e-4 and 12.3E+4 as a single token.
+				if !(len(t) > 0 && t[0] >= '0' && t[0] <= '9' && (t[len(t)-1] == 'e' || t[len(t)-1] == 'E')) {
+					break
+				}
+			} else {
+				break
+			}
 		}
 		in.readRune()
 	}

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

@@ -3,6 +3,24 @@ numbers = [
     11,
     123.456,
     123.,
-    .456,
+    0.456,
     1.23e45,
+    -1,
+    +1,
+    0.0,
+    -0.0,
+    1.0,
+    -1.0,
+    +1.0,
+    1e6,
+    -1e6,
+    -1.23e-45,
+    3.539537889086625e24,
+    3.539537889086625e24,
+    3.539537889086625e24000,
+    3.539537889086625e24000,
+    3539537889086624823140625,
+    0x123,
+    0xE45,
+    0xe45,
 ]

build/testdata/003.in

@@ -5,4 +5,22 @@ numbers = [
   123.,
   .456,
   1.23e45,
+  -1,
+  +1,
+  0.0,
+  -0.0,
+  1.0,
+  -1.0,
+  +1.0,
+  1e6,
+  -1e6,
+  -1.23e-45,
+  3.539537889086625e+24,
+  3.539537889086625E+24,
+  3.539537889086625e00024000,
+  3.539537889086625e+00024000,
+  3539537889086624823140625,
+  0x123,
+  0xE45,
+  0xe45,
 ]