cue/format: pad floats with leading or trailing periods

This is just a readability thing and does what your typical
spreadsheet does.

Also if we every want to allow paths like `a.1` and paths
with a leading `.`, the presence of `.1` is, albeit not
necessarily ambiguous, at least confusing.

Change-Id: I66490c5f7d9746b20d23c0eb69ee3dd0b89c25c3
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/7742
Reviewed-by: Paul Jolly <[email protected]>
Reviewed-by: Marcel van Lohuizen <[email protected]>
Reviewed-by: CUE cueckoo <[email protected]>

Author: mpvl

cue/format/printer.go

@@ -133,7 +133,22 @@ func (p *printer) Print(v interface{}) {
 				data[1] >= '0' && data[1] <= '9' {
 				data = "0o" + data[1:]
 			}
+			// Pad trailing dot before multiplier.
+			if p := strings.IndexByte(data, '.'); p >= 0 && data[p+1] > '9' {
+				data = data[:p+1] + "0" + data[p+1:]
+			}
+
 		case token.FLOAT:
+			// Pad leading or trailing dots.
+			switch p := strings.IndexByte(data, '.'); {
+			case p < 0:
+			case p == 0:
+				data = "0" + data
+			case p == len(data)-1:
+				data += "0"
+			case data[p+1] > '9':
+				data = data[:p+1] + "0" + data[p+1:]
+			}
 			if strings.IndexByte(data, 'E') != -1 {
 				data = strings.ToLower(data)
 			}

cue/format/testdata/values.golden

@@ -2,5 +2,13 @@ a: 0e+1
 a: 0e1
 a: 0e+1
 a: 0e1
-a: .3e+1
-a: .3e+1
+a: 0.3e+1
+a: 0.3e+1
+a: 0.3
+a: 3.0
+a: 3.0T
+a: 3.0e100
+
+s: """
+	x\"\"\"
+	"""

cue/format/testdata/values.input

@@ -4,3 +4,12 @@ a: 0E+1
 a: 0E1
 a: .3e+1
 a: .3E+1
+a: .3
+a: 3.
+a: 3.T
+a: 3.e100
+
+
+s: """
+    x\"\"\"
+    """

internal/third_party/yaml/decode_test.go

@@ -56,7 +56,7 @@ var unmarshalTests = []struct {
 		"v: 0.1",
 	}, {
 		"v: .1",
-		"v: .1",
+		"v: 0.1",
 	}, {
 		"v: .Inf",
 		"v: +Inf",
@@ -68,7 +68,7 @@ var unmarshalTests = []struct {
 		"v: -10",
 	}, {
 		"v: -.1",
-		"v: -.1",
+		"v: -0.1",
 	},
 
 	// Simple values.